I have 91 RS that is basically stock with a 305 and 224,000 plus miles. A few weeks back the AC quit working. I thought it was the relay mounted by the blower motor so I bought a new one to replace the burned up one (which was burned up) but no luck. The AC system was replaced with new parts about two years ago, new compressor and dryer. I also replaced the plug for the relay by the blower motor about three years ago because it was burning out relays.

Heres what I have found out so far. The new relay itself is good, I checked it out by trying it in place of the fan relay by the brake master cylinder and the fan came on. If I jump the main power wire (purple I think it is to the red) on the plug by the blower motor it will come on, I can also jump the wires at the plug to make the clutch on the compressor engage. But with the new relay in place nothing happens.

Also, a while back I was having similar issues and while fooling around I jumped the plug on the front of the compressor and somehow everything worked again. Then it quit again on me. After messing with this plug for a while I got it to work again and all was well for about 6-7 months until recently. I have checked all I can think of, fuses, relays, voltage, continuity, but somewhere there is something I am missing and if anyone could give me any advice or help I would really appreciate it.

I have also posted this in the cooling section as well.

Thanks, Chris

 

So what does not work, the compressor or the blower motor? They are two separate circuits. The blower fan relay does not control the A/C compressor.

Btw, if you jump/short the plug on the A/C compressor, it won't come on, it will blow the HTR A/C fuse. So don't do that.

 

Neither works when I switch the AC on, only the radiator cooling fan. I haven't jumped the plug on the front of the compressor this time. It was months back just fooling around with a test light that I accidently did that. When it was jumped the blower motor came on and everything worked again. But it seems to be the same problem.

You said the relay for the blower motor won't control the compressor? But why does the clutch engage when I jump the wires (orange to black) at the plug for the blower motor relay? And what is the plug on the back of the compressor for? Whatever the problem is it's affecting both the blower motor and the compressor.

 

Is your HTR A/C fuse good?
The only way jumping the red and purple wires on the blower relay could engage the A/C clutch would be if the HVAC panel was set to cool and it was backfeeding the power from the blower to the A/C circuit. Otherwise those circuits are separate, as I mentioned and they should not affect each other.
Do not jump the orange to black on the blower high-speed relay, that will short the circuit and blow the fuse. Which might be blown then, I would check it with an ohm-meter.

 

It's actually the red to orange that makes the compressor clutch engage when jumped. Where is the HTR fuse at? Under the dash? I have checked all the fuses I can think of and visually see, and they all appear to be good.

 

Yes, red to orange makes perfect sense and it sounds like a blown fuse then because you are back feeding power from the red wire, through the orange wire to the brown wire and then to the compressor clutch.
http://www.austinthirdgen.org/mkport...F_and_vin8.jpg
http://www.austinthirdgen.org/mkport...C60_manual.jpg

Yes, the HTR A/C fuse is under the dash. Please do believe me when I say that it can look good but might not be good. There have been plenty of instances here on TGO alone where a visual check of the fuse labeled it good but the fuse was actually blown.

If you have a test light (or voltmeter), please check that you have power on both sides of the fuse. If you do, you might have a wiring problem then.

 

Visual exam of the fuse does not always work. I made that mistake on the gage cluster of my car and chased wiring and diagrams for a week until I changed the fuse anyhow. Voila, it worked. Use a volt/ohm meter and test for voltage on both sides, or continuity through the fuse. It may just have a bad connection at the fuse.

 

Fuse is good, even tried another one with no luck. Im gettin a little over 12 volts at the fuse plug. The blower motor relay plug is getting a little over 12 volts as well. Basically something is not letting the relay kick on or let the clutch on the compressor engage. Could it be something to do with the HVAC controls in the car itself? It got damaged a few months back (had a bad day) but was working fine before this. Also before this happened I lost the ability to run the blower motor on the highest setting. Could there be something to do with that happening? Seems like thats what happened before and all I had to do was replace the relay.

I do appreciate the help and I'll keep digging around until I fix it, or it cools off enought I don't need it.

 

I have also been getting a check engine light everytime I drive after about 10 minutes. I just checked and it says code 53, system voltage too high.

 

Yes, a damaged HVAC panel would account for all your issues, for sure.

Do you see more than 15 volts while driving? Otherwise code 53 might be the wrong code.

 

Not sure on the voltage, never pay much attention to it. But I don't think it ever goes above 13 volts. I did the paperclip trick and thats what I came up with. Seems like an odd code to me though. Need to clear it out and see if it comes back.

I looked at the HVAC controls too as best I could, but I couldn't get it all the way out to really look it over. The mounting tabs are broke and the whole assembly will have to be replaced at some point. But it will be a while before that happens. I think you may be right on this one, but my only question is, if if were the controls would the fan still come on or not? It still works when I switch the AC on.

Thanks for the help and suggestions.

 

Good question.
On the TBI models, the HVAC panel grounds the coolant fan relay when you move it into the A/C or MAX A/C position. That circuit might work while the others don't because this circuit switches ground instead of the brown fused power wire.
When you pull the HVAC panel, you can check the brown wire for power. If it does have power but sends no power out to the blower fan (orange, light blue, tan or yellow wire - based on fan speed selected) or the A/C compressor clutch (light green), the problem is in the panel. Easy to replace, easy to find a replacement too. I might even have one or two in the garage.

Let us know what you find.

Regards
Lou

 

Problem fixed. It turned out it was the pllug on the back of the HVAC controls. The brown wire wasn't seated in the plug and it was losing connection. It works now but will have to replaced later on.

Thanks again for the help Lou.

 

Thanks for posting back your solution, it will hopefully help somebody down the road if they find your thread.