TAC Tech => Electrical => Topic started by: firebirdparts on January 16, 2013, 08:36:26 AM

Title: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on January 16, 2013, 08:36:26 AM
We get many questions about A/C wiring, mostly connected to issues with the blower.

Here is the 78 wiring diagram for A/C:
(http://www.firebirdtransamparts.com/forumposts/78acwiring.jpg)
Years other than 1978 differ a little bit in two ways:

1.  The control head interacts with blower speed a little bit differently for different years.  This is not a big deal.  Since "low" fan speed does not ever need to be off, it does not need to go through the switches at all, and that is how a 78 is.  Some years have a "real" set of contacts in the switch for low fan speed.  For some years, MAX a/c has a set of contacts that bypass the fan speed switch, resulting in high fan speed all the time in MAX A/C.

2.  The cold controls that turn the compressor off vary from year to year and a little bit with engine choice.  In every case, all the components that can cut the compressor off are in series, so they have to all agree for it to be on.
Title: Re: A/C Wiring Diagram
Post by: firebirdparts on January 17, 2013, 09:15:21 AM
There are three major things you need to know about the blower wiring, in addition to the fact that the fan is always on, even in the "off" position.
1.  There's a ground wire.  The blower and the relay are mounted in plastic, and they need a ground wire.  For most engines, the ground was on the compressor brackets with the compressor clutch ground.  There's a plug, called the "compressor harn line conn" in this diagram.  If you unplug that, the blower will stop.  If you remove your compressor brackets, the blower will stop (for most engines).

2.  There are two power supplies for the blower.  High speed is powered off the back of the alternator for most engines, circuit #2, red, in this diagram.  There is a connector in that line, or maybe two, and these get hot and corrode.   Expect problems.  Lower speeds are powered by the heater fuse, which sends power through wires 50A, 50B (brown) under the dash, plugs into the A/C harness, and powers all the controls there, and eventually goes through the resistors and the compressor cold controls.

3.  The relay is a double-throw.  It sees a big red wire with 12V coming from the alternator, and reduced power coming from the resistors.  It has to choose between those two, and connect one of those two items to the blower motor.  When the coil is powered by circuit 52, it chooses high.  If the coil is off, it chooses the resistors.  The coil is turned on by the A/C control head under the dash.
Title: Re: A/C Wiring Diagram
Post by: ILLTA77 on January 17, 2013, 10:17:34 AM
great write up,  most of us who have and use the A/C will run into some of these wiring/connector issues failing at some time. Until you work on several, you just dont know where to begin.  A shop manual is needed, they seemed to change the wiring every few years due to improvements in the A/C system parts.  TXV, VIR, CCOT  all different systems used over the years in Firebirds
Title: Re: A/C Wiring Diagram
Post by: 800qjet on January 17, 2013, 04:35:48 PM
Thanks for the great writeup. As usual, you have been most helpful.
Title: Re: A/C Wiring Diagram
Post by: firebirdparts on January 18, 2013, 11:55:20 AM
Thanks, guys.  Everybody has trouble with this sometime.
Title: Re: A/C Wiring Diagram
Post by: BlueTTA on January 18, 2013, 12:36:32 PM
Here is a drawing for 1980.      (Figure 1B-3 F Series C60 A/C Wiring)

(http://i249.photobucket.com/albums/gg227/Blue80TTA/Electrical%20drawings/1980F-SeriesAirConditioning_zps34c078ea.png)

Personally, I disagree with the drawing for the (T) VIN because there is no Idle Stop Solenoid and no Wide Open Throttle switch.
So the Turbo should look much more like the (W) or 301 N/A sub drawing.

To save it, just right click on the drawing and save as a .PNG file.  Then you will be able to zoom on the file to read the details.
Title: Re: A/C Wiring Diagram
Post by: firebirdparts on January 18, 2013, 01:47:57 PM
They must have changed their minds.

I have only seen one with WOT A/C cutout, and that was on a 1977 Formula, 301, 2-barrel.
Title: Re: A/C Wiring Diagram
Post by: 800qjet on January 18, 2013, 02:23:13 PM
I'll keep looking for info on the WOT switch. I have a switch and wiring and hope to adapt it to the Qjet 4 bbl. Might be good for the AC compressor. I had a new '78 GP with the 301 two bbl. and it had the WOT on a Rochester Dualjet 210.
Title: Re: A/C Wiring Diagram
Post by: jjr on January 20, 2013, 05:26:43 PM

 1980, VIN code T... with WOT switch...

(http://www.301garage.com/forum_pics/1980_301T_Engine_wire_harness.gif)

 Joe
Title: Re: A/C Wiring Diagram
Post by: 800qjet on January 20, 2013, 05:42:27 PM
Thanks, I printed the wiring diagram. That will help sort out my box of wiring. I asked on the 301 forum about pix of the linkage side of the Dualjet 210.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Mint 1973 on December 08, 2013, 06:02:33 AM
Anyone have 1973 a/c wiring?
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on December 08, 2013, 07:14:18 PM
Factory shop manual is pretty awesome.  you'll love it.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Farmer2 on December 29, 2014, 07:29:49 AM
Wiring Question. I have two red hot wires coming off the same terminal of the altenator. One goes to the battery and the other has a 10" lead and a white plastic connector that goes to nothing. In alot of the photos of your cars I see this lead and it looks like it goes across the manifold to the pass side and I loose it after the ac compressor. Can someone let me know if I need to remove this or wire it in where it goes and someone short cutted it. I have a 1978 TA 400 with no AC just heat.

I looked at the schematic listed here and it looks like it would be for the high speed of the blower motor. I dont and never had ac on this car. I dont know what the previous owner did with this wire.

Thanks, Dave
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on December 30, 2014, 08:23:03 AM
Remove it.  If you think it's original, it may be a factory mistake.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Farmer2 on December 30, 2014, 09:16:26 AM
Thanks guys. I found it in an online schematic and it is for the ac relay if I had it. I will remove it. It has its own eyelet so no biggy. just wanted to make sure it wasnt from something a previous owner disconnected.

Dave
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 10, 2015, 02:15:06 AM
Alright, so I have a '79 A/C car that someone decided to remove the compressor and bracket.  So from what I'm reading this is the reason why the blower motor won't turn on at all?  I'd like to have at least the blower motor working for now to circulate air and for heat/defrost when needed.  Is all I need to do is go and run a wire from the harness ground that'd normally go into the compressor to a good grounding point, like the block, in order for the blower to work again?  Any help would be greatly appreciated.  According to the previous owner it was because of the relay, so after buying a new one and installing it only for it to still not work is kind of irritating.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on February 10, 2015, 07:40:52 AM
Yes, that is the first thing you should do.  That wire is black. 

If that does not fix it, it'll be time for the test light after that.  If you want to pre-empt us,  you could check the heater fuse too.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on February 10, 2015, 02:25:57 PM
P.S. Chevy-powered cars may orginally be grounded to the firewall instead.  Was yours originally a chevy 350 car? 
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 10, 2015, 09:09:47 PM
I found the compressor harness and plugged it into the harness next to the blower box and condenser, then put the ground onto the alternator bracket.  I also noticed the positive wire next to the compressor harness that plugs into the alternator wasn't connected, so I found that wire and plugged it into the harness and into the alternator.  Though doing that the positive wire from the battery to the alternator will need redone, as the previous owner had it where that other wire plugs in.  So I'll need to fix the battery to alternator wire before I can check and see again, as now the car doesn't have power.

I replaced all of the fuses shortly after buying it.  From the VIN it was originally a 301 car, and the drivetrain is swapped.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 10, 2015, 11:31:32 PM
Alright, finished the wiring and with the key in the ON position I can hear the relay clicking by moving the sliders on the climate control.  Blower motor isn't turning on though, I wouldn't think the car not running would make a difference.  The heater resistor is intact with no burn marks or anything, so I'd think it's ok too.  Unless the relay isn't bridging the contacts even though it's clicking.  I had put the old relay back in after the new one didn't help last time, I guess I can try swapping them tomorrow when I don't have to fumble around with a flashlight.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on February 11, 2015, 07:44:54 AM
You need to use a test light, see where you have power.

Some tips:
The relay should only click when you are on "HI" fan speed.
The power supply for the lower fan speeds is through the heater fuse.
The fan runs on low when the ignition is on, but the a/c slider is "off."  Low fan speed is the same thing as off.

Also, something here bothers me:
Quote
I also noticed the positive wire next to the compressor harness that plugs into the alternator wasn't connected, so I found that wire and plugged it into the harness and into the alternator.  Though doing that the positive wire from the battery to the alternator will need redone, as the previous owner had it where that other wire plugs in

That is not right.  The red wire feeding the blower goes to the screw post on the alternator.  You just stack it on top of the charge wire.  Two wires on that post. 
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 11, 2015, 02:57:31 PM
I have a test light, so will use that.  Being the low speed doesn't need the relay, it could be the motor then I suppose.  I guess worst case this weekend when I have more time I'll get to the motor and supply it with power straight off the battery to test it.

I'll pay more attention when I go and do more testing, but I think it clicked more than what it should.

The wire is on the alternator post, just a small piece of wire with a clip on it that ends in a ring connector on the post.  I looked at my brother's original 301 car and this was how it was done as well with the same wire and clips between the harness and alternator.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 11, 2015, 02:58:17 PM
Also, thanks for being so helpful! 8)
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 13, 2015, 04:19:27 PM
Got it working somewhat, the motor will start to spin but does it very slowly.  I suppose it needs to be replaced then.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on February 13, 2015, 07:51:10 PM
It might.  If I were you, I would jumper my way over there will full battery power and see what happens.  Getting that blower out of there is not fun.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Box on February 13, 2015, 08:53:25 PM
Was going to do that to double check before buying one and going through the hassle.  It started working out of the blue,  was just sitting there with the key in the ON position and all of a sudden I hear a rumbling sound.  At first I was like ahhh, then I realized it was the motor.  The relay clicks going to high, and then clicks when moving from off to whatever zone but only when the fan is on high.  I suppose that's how it's supposed to work since it's going off the fuse panel until then.  If anything I've learned why so few have working heat and air now.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: peter panov on July 24, 2015, 01:17:09 AM
Hello,

Please advise.
I am trying to restore my A/C electrical system on a 1978 Trans am with L78 engine.
If you look at the wiring diagram in the first post, there is a wire 987B-18 grn lt/blk that goes from the thermal switch to a compressor harness connector. After that it turns into 67-18 blu lt and goes to an idle stop solenoid (L80 only). In my case, I have an L78 where will 987B-18 grn lt/blk go after the compressor harness connector? I am missing everything after this connector and this is the only wire that I can not figure out where to place.

Thank you!
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on July 24, 2015, 06:46:07 AM
That circuit is only used to turn on the idle speed solenoid.  If you don't have one, then it goes nowhere.  I am not sure I believe that is L80 only, but it's not that important.  If you have the solenoid, then use it.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: peter panov on July 27, 2015, 05:04:55 AM
Thank you!
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: elgordo77 on January 05, 2017, 10:08:56 PM
Hope someone can help me. I have a 77 TA 403 K Vin. I am fixing and having trouble on where wire goes from a sensor that is next to passenger door inside fender next to blower it is one wire in and one wire out of sensor the previous owner connected the two wires to be one and  just was hanging next to air vent fender,he also put all wrong wires in car under hood. System works but I am still would like to know where it plugs into if it is important to connect it?
Thanks
John
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Aus78Formula on January 05, 2017, 11:05:05 PM
John, Does the aircon actually work or just the fan? Sounds like the 'sensor' might be the pressure switch which is normally mounted on the aluminium drier and sometimes a second one mid-line in the tubing. These drop out when the AC pressure is too high or too low, essentially overcharging and freezing up, or a leaked system. You can bypass these by running the wires across them but the only reason to is to cover up another fault. Sounds fairly messed up anyway. Some also had a temperature switch on the case for similar reasons, and similar ways around. When there's more than one switch it's possible to still bypass some and operate. Later years dropped the extras.

Start a new thread, add a few pics, and we'll soon be able to tell you what's going on and what to do.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: cwi inspector on March 16, 2017, 07:01:34 AM
I have a 79 Trans Am with the 403. I recently replaced the under dash wiring harness as well as the AC harness. Everything works as it should. I am putting the AC back on this car as the original AC was removed by a previous owner. I do not have the AC compressor hooked up electrically as of yet. My issue is I have the blower motor working however the ground wire that is in the harness isn't grounding so I grounded the blower motor to the body of the car. When I hook the blower motor up it drains my battery over night. I have replaced the resistor, relay, both switches on the controls and the blower motor. I'm at a loss as to what may be draining my battery. Also I can not get the motor to work in the HI position.  I am installing a Classic Auto Air system. The only wire that connects to this compressor is the power wire. I was told by Classic Auto Air the plug that is plugged into the OEM compressor is no longer needed as the compressor is self grounding through the mounting brackets. There is no connection on the CAA compressor for that connector to be plugged in. Any help or ideas on where to go from here would be greatly appreciated.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on March 16, 2017, 08:07:23 AM
CWI inspector, welcome to TAC!

There are several paths that might cause your battery to drain.  I guess that is always true.  The high fan speed relay is always powered, so that might be a place to start.  Since high fan speed doesn't work, I don't know for sure that yours is actually powered, but it might be.  If power escapes from there with the ignition off, then the relay itself is bad.  They are not supposed to do that.  You can easily unplug the relay and let that be an experiment.

The heater fuse should be unpowered with the ignition off, so power coming that way is not supposed to be the problem.  You could consider double-checking that the heater fuse wire is dead when it's supposed to be.  There are separate contacts in the ignition switch for that circuit.

The relay has to be grounded to work, so if you are not using the original ground wire yet, that could be the reason that the high fan speed does not work.

Self grounding compressor will be great, just use the green wire to the compressor to turn it on.  The black ground wire still needs to be grounded somewhere.  Originally it grounded the compressor, fan, and relay.  You still need something to ground the fan and relay.
Title: Re: A/C Wiring Diagram and A/C Blower How
Post by: cwi inspector on March 16, 2017, 11:18:48 AM
I have replaced the relay on the side of the evaporator core box twice with no luck and tried the old one as well trying to get the blower to work on hi. Is this relay the same as the hi blower relay. If they are different where is the hi blower relay located? I had the dash board out and there was what looked like a relay mounted to the back side of the dash board. I hope that's not it. I do not want to have to pull the dash again.
Update. I was looking at the diagram at the top of the page and there is no wire leading from the starter to the red wire in the AC harness. Correct me if I'm wrong. Once I connect the red wire to the starter I should have Hi speed on my blower. should this red wire be hooked to the solenoid of the starter or to the positive terminal. This doesn't sound logical but could this be the reason the battery is being drained? I apologize for asking so many questions but previous owners of this car molested the crap out of the electrical system and tore the ac out. That's why I replaced the under dash harness. I really appreciate your help. Thank You.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on March 16, 2017, 06:37:38 PM
that is the correct relay.  As I said, that is just a place to start.  The relay under the dash is rear defrost. 

The red wire powers high fan speed.  You will need that to get high fan speed to work.  however, the battery is not draining through that wire if it's not hooked up. 

That wire comes from battery power.  Battery power is available on the starter where the battery cable is connected.  That's where it hooks to.  There is supposed to be a fusible link in there (a wire which melts if you get in trouble).  You need some protection since that wire doesn't go through the fuse box and comes straight from the battery cable.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: cwi inspector on March 16, 2017, 07:09:39 PM
Thanks for all the information and help. Hopefully I can get this figured out now.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: cwi inspector on March 18, 2017, 06:48:27 PM
I have everything hooked up and the blower motor works as it should even on high. The electrical to the compressor is hooked up and working. I still have the electrical draw on the blower motor. I start the car and my volt gauge usually always reads 13 to 14 volts. When I turn on the blower motor it drops to 11 and takes a while to go back up once I turn the fan off. I'm at a total loss.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on March 18, 2017, 09:06:28 PM
The blower takes quite a bit of power, but it wouldn't really suck the voltage down to 11 volts.  I am thinking that problem may be something else, but even if it is the blower, if the battery is running down, I say fix that first.    The blower is not supposed to be able to get power when the ignition is off.  So you've got some bypassing or something elsewhere in the system.

You really did not mention whether the blower runs when the ignition is off.  If power is going through the blower, it could be running.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: cwi inspector on March 19, 2017, 08:31:47 AM
No the blower does not run when the ignition is off. That's why I'm at a loss. The battery drains when the blower is plugged in. When I unplug it the battery stays charged. With the wiring harness being new, switches new, resister new, relay new and new blower motor this should not be happening. Everything as far as I can tell is hooked up the way it should be.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on March 19, 2017, 11:00:21 AM
Do you have a volt meter or a test light?  If there is power to the blower with the ignition off, you need to see which wire has power, then work back along that wire.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: cwi inspector on March 19, 2017, 01:52:55 PM
Traced the problem back to the ignition switch. Changed that and I believe the problem is solved. The test light would light up when I put it on the blower fan connection with the ignition off. Traced back along the circuit testing all switches. Still had power to those with the ignition off. The only thing left was the ignition switch. Changed that out and now the test light goes out when the ignition is turned off. I hope that fixed it. I guess I will find out later if the battery is still charged. Once again thanks for all your help.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Amigo-2k on June 03, 2017, 07:19:36 AM
I have a 1977 TA with an LS swap with AC and the blower motor only seems to have 1 speed (low).   Reading through this, it sounds like I need some sort of ground to fix this?

Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: lund85 on June 13, 2017, 01:02:59 PM
I hope someone is still watching this thread.  i have an interesting issue with my blower ive got it working 90% of the time, but ran into an issue when i charged the a/c the blower works on all settings except 1 when set to max ac the blower drops to low no matter what the setting but works fine on normal and bi-level not max 
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: lund85 on June 22, 2017, 06:08:34 AM
sorry i forgot to add it is a 78 trans am with 400
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on June 22, 2017, 09:14:02 AM
That is a bit odd.  Here is my guess as to the reason:

On some years Max AC was supposed to force the blower to HIGH and as a result, there is a separate wire that powers the fan on Max AC.  [Edit]  78's don't have this wire.  I think you got earlier model controls and 1978 wiring which doesn't match exactly.  If it's anything like that, I think you can jumper two pins on the control head and you'll be okay.  The wiring diagram for 78 posted here shows that the control head still has the pin but there's no wire. 
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: via3d on October 12, 2017, 11:41:25 AM
I noticed the same issue. Did you ever find resolve?

I am replacing my heater core and with everything apart now, I decided to test AC, determine if it works and blows cold, if so I will leave alone. If it doesn't blow cold, I might as convert to R134a.

3 items/issues:
1) -->> When I set the AC to MAX  and the fan to Hi (max setting out of 4) the blower doesn't spin at all....
.....matter of fact it doesn't spin at all on any setting setting AC, Heater etc.  !! 

2) compressor clutch is not coming on.... is there a bypass/jumper method that I could do to tell if compressor is o.k.?

3) the fan stays on low at all times when key is in ignition on start or run  (all settings" on , off, heater, Ac , etc.)


as the whole heater box under console is out, the only the vacuum small tubes are all disconnected on heater box and kick panel...  all wiring is connected.

I have 2 wires going to the blower black and brown with rubber boot.
The 4 wires going to blower resistor,
4 more wires going to silver box (what is this?)
green and blue wire connector to accumulator
and the 2 wires hot and ground going to compressor.




Jason
1979 Firebird TA (.403 olds K model)
 
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on October 12, 2017, 04:08:59 PM
If you have low fan speed, then that means that the heater fuse has power.

The system gives a lot of trouble, as you can see in this thread.  If the blower does not want to work just in max AC, then that sounds like a switch issue on the controller, or a simple wiring issue there between the switches.

The mode controller has contacts that allow the blower to run in each setting that is not "off".  This is just a simple feature.  When "off" the fan drops back to low speed.  When "on" the fan switch then gets power, and there is a wire connecting those two, the mode controller contacts to the fan speed switch.  From the fan speed switch, there are 3 circuits coming out, so I think that is not your problem.  You can check by seeing if you can get power to anything on the resistors other than "low".

If the compressor won't run, I would bet you're low on freon.  You can check that, yes, by jumping at the evaporator accumulator.  You should have power coming there when A/C is selected, so troubleshoot that if you don't.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: via3d on October 13, 2017, 09:39:48 AM
Firebirdparts, thanks for quick reply. I am in the thick of this now working on her.

to be sure - "mode controller"  - your referring to dash controls?

I may have confused things in my writ. In summary:

A. low is always on, when controls or off and car running or key in start/run position.  Is this correct and acceptable?

B. AC MAX setting, blower fan does not operate.
Question B1: All others seem to operate fine. Is this because the compressor clutch isn't engaging?
Question B2:   

C. Compressor clutch does not come on at all with dash controls.  You indicated this may be freon low...
The clutch DOES run when I jump it at the accumulator pins.
Question C1: Does this mean the compressor is o.k. , and most likely freon is low? 
Question C2: Can I run it a few minutes with it jumped... long enough to check the freon level with gauges?

Sidenote: I have the r134A fittings and newer gauges so I can test.
Seemed odd the retro-fittings... high side is in on the accumulator? and lowside on railing leading to evaporator ?

E. If freon is low, can I use hotshot or some similar alternative for the time being?

F. If answer is yes to E  Is it better to go ahead and convert to R134a??   (vacuum, new accumulator and expansion valve, fill to 80% freon level)

...apologies for the bombardment... I am steadily trying to get her running currently.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on October 13, 2017, 03:21:19 PM
A: Yes
B:  No
C:  You are low on freon.  Do not run the compressor, no need.  you can just put the gauges on.  if you have 30 psi or more, then maybe it should have come on, and maybe we might suspect the pressure switch.  However, I would bet it's low.  These compressors leak.
DEF:  We have had many threads on refrigerant conversion, and of course the conclusions for a Trans Am are not very different from any other formerly R12 car.  There are pros and cons of several options.  R134A is certainly cheap.  R12 is still available reclaimed.  The original a/c system will leak.  I would say look at some other threads on this.  I think an abrupt change to 134A is probably the cheapest option, but you need to leak check with something.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: via3d on October 14, 2017, 02:59:57 PM
Firebirdparts, others ~

Blower motor not work on HI setting.

I am at a loss what to do at the moment regarding ?   

- AC compressor relay?
- Blower resistor - doubt this is the issue right ? all other settings work....
- Take the dash controller out and inspect contacts ?

O.K. Dash controller out.
Reading posts and I agree, doubtful it is the blower resistor.
--->>>  When I switch to HI on the controller,  The AC compressor relay has a real loud clicking noise. No other setting does it. Doesn't matter the selection on the dash (ac, normal, heat, etc.)

BAD RELAY?

Is there a means to jumper to test the blower motor on HI setting? This way the blower is eliminated and VIOLA - it must be the relay?

I found your post w/ wiring diagram for a 78 TA...  it will take me awhile comprehend it if I can at all ...  LOL

I am trying yo finish my original problem (heater core) but need to make sure the blower motor is fine.
I can retro-fit or do whatever with the AC later, but I need to get the heater core done and the car back together. 
It only leaves the evap not accessible (I figure low risk, chancing the evap will work).
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on October 14, 2017, 03:56:38 PM
You can't inspect the contacts, I don't suppose.  You might be able to get some contact cleaner in there.  I have never really tried to take that switch apart, so I may be wrong.  the switch where it sits on the mode controller should be pretty obvious.  What's not obvious is that the MAX AC setting had its own unique contacts.

This thread in which you are posting is the sticky wiring diagram thread.  You can apply 12 volts to whatever you want to except for the ground wire.

If High fan speed is not working, there are a lot of components involved in that.  You'd be crazy not to use a volt meter here.  You need power on two wires to the relay for it to work.  If you get that, then you need the relay to turn on.

Your question about a jumper connecting the compressor to the blower:  don't.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: via3d on October 14, 2017, 04:55:33 PM
I updated my above post firebirdparts while you posted ... LOL

anyways UPDATE:

Controller out now.

The switch is basic... at first look burnt but its not. there was goo glue that just aged like molasses (how switch was made with adhesive). 

What I notice now with car not running, only key in start....
There is a loud clicking noise in the compressor relay when the HI setting is selected. Doesn't matter the dash setting (heat, AC, norm, etc).

Is this really supposed to click loudly on HI only (and not operate)?  no other mode selection or fan setting does this. 

this means power is getting to the relay at least...     BUT leaves relay or blower motor as culprit. Almost narrowed down.

I have volt meter just need to figure out  what 12v to where.

Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: via3d on October 14, 2017, 10:10:52 PM
Ok All,

ISSUE: the Fan Blower is not working on HI.... All other settings for the blower fan work fine.
CAUSE: Wiring connector !!!

Possible causes:
1) Blower resistor - if other fan settings are working, the resistor likely is fine
2) Blower relay - not sure how to check, check for 12v to and from perhaps. I checked voltages for 12v at the hot wire to the blower. noticed HI fan setting only produced 3.5-4v here.
Relay had power, you could here in click loud most tomes when set HI on and off , with only key in ignition on start not run
3) Blower - not sure how to test really - it works or it doesn't perhaps.... since it worked on all other settings I didn't think this was an issue.  However for peace of mind vs. a 38 years blower, I replaced mine for less than $20 since everything was apart (a major job)
4) Mode controller - bad switch (IMO least likely)
5) Wiring/connectors


My issue / SOLUTION:  Wiring connector  !!!!!!!!!  clean crimp and di-electric grease.  I traced the wiring and discovered a serious voltage drop when set to HI on the alternator hot wire that feeds this blower circuit.

See this post for some details on possible other sympyoms leading to same cause/solution.
http://transamcountry.com/community/index.php?topic=77959.msg735900#msg735900 (http://transamcountry.com/community/index.php?topic=77959.msg735900#msg735900)


Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: glhx on June 10, 2018, 05:18:29 PM
This is a standard wiring diagram for the 1978 model year. It’s just a color version of the one posted in the first post.

(https://farm2.staticflickr.com/1809/41141655110_374dddfeed_b.jpg) (https://flic.kr/p/25FxJHd) (https://flic.kr/p/25FxJHd)





This one is a 1979 version
It’s accurate to the car. I’ve based it off of the 1978 version above but made this one from my own car. Some of the wire colors are different and no thermoswitch

(https://farm2.staticflickr.com/1770/28082264147_fe81a1d015_b.jpg) (https://flic.kr/p/JMwWL4)  (https://flic.kr/p/JMwWL4)
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Fuzzy on April 12, 2019, 02:39:53 PM
Here is my issue(s):

I have no speed control to the blower motor at all (for the longest time I have everything but High).
-I tried replaceing the High blower relay, that didn't fix anything.  is this a switch, resistor or something else problem?

The compressor doesn't turn on when I slide the lever over to it



Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Aus78Formula on April 12, 2019, 06:19:14 PM
Many things affect the aircon system. The compressor doesn't turn on, it simply engages and disengages the clutch behind the pulley. For that to even occur the power must have got past the pressure switch (es) meaning there's suitable pressure in the lines for it to operate. The pressure switches can also stick and fail. You can check if you have power at this point by unplugging the pressure switch and checking the plug terminal with a test light when the AC mode is selected. Running off the same feed is the compressor clutch, is it locking and unlocking when AC selected? There's also a live wire running to the carb idle solenoid. If none of these activate then you need to look at the pressure switch or prior. If the solenoid works but not the clutch, run some wires directly to the compressor terminal to test direct.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Aus78Formula on April 12, 2019, 06:22:48 PM
Ok ignore that, not sure where the post went that I replied to....??
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on April 13, 2019, 02:34:38 AM
Here is my issue(s):

I have no speed control to the blower motor at all (for the longest time I have everything but High).
-I tried replaceing the High blower relay, that didn't fix anything.  is this a switch, resistor or something else problem?

The compressor doesn't turn on when I slide the lever over to it

Sounds like you blew the heater fuse.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Fuzzy on April 13, 2019, 08:05:45 AM
thanks, I'll check it out.

The blower still turns on "off" but I don't know if there is another source of power for all the others
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Aus78Formula on April 13, 2019, 08:46:45 AM
Not sure what you meant, there's no Off for fan on an AC model.
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: Fuzzy on April 13, 2019, 02:14:40 PM
That's what I meant,  even though none of the other fan settings work, the fan still blows on when off.

I was asking is if the fuse is blown, would it still blows when off (I know it's supposed to blow on low when in off position)
Title: Re: A/C Wiring Diagram and A/C Blower How-tos
Post by: firebirdparts on April 14, 2019, 12:15:11 PM
Okay, well, the fuse is not blown if the fan is blowing on low all the time.  On the back of the a/c controls, there is a sort of a harmonica shaped connector.  If that slips off, it disables everything but leaves the fan blowing on low all the time.  So that's my second guess.