1980s 1980 350 Eldorado AC Compressor Never shuts Off

[Turboba6]

Hi Folks,

  Of course being a 1980, I have the 1 year only (maybe 81 too I guess) and the Problem I have is that the Compressor Never shuts off (unless I unplug it of course) I Replaced the InDash head unit as well as the Below Glovebox Controller with a Known good one ... when the head unit is in the Off Position the compressor Still circulates on and off.. I Bought 2 remanned Under Hood Controllers but they were rebuilds and were Both bad..the Compressor is Original and the AC was converted and works well...

Thanks!!

[TJ Hopland]

I will have to find my manual but from memory there wasn't anything fancy going on in the blower module, it was just an electronic relay.   There was a single wire from inside that I think would ground when the clutch was supposed to be engaged.  In my 80 that section had failed.  I was able to bypass the module and used a universal relay.   So you should be able to find that wire and determine if the signal form inside is working or if when you disconnect it from the module does the clutch disengage?.  If it does then its not the module.  IF it still stays on its the module.   

I'm pretty sure what killed it was a replacement clutch that drew too much power.  I don't remember the numbers at the moment but back when that happened I had what appeared to be an original compressor and clutch to measure the draw on and it was something like 3 amps.  The compressor I was running which didn't look original drew more like 7 so way more than intended.  I remember I could see a burn spot in the epoxy in the blower module.

[Turboba6]

Thanks TJ, yes gonna look over the wiring diagram, I'll find the culprit and report back...Thanks!!

[TJ Hopland]

I found my book.  Gray/white wire(s) are the signal wires.  I didn't remember there being 2 but they get combined just before they get to the blower module so I guess I never looked further.  One comes from the ECC control module which is the part with the display and buttons nad the other comes from the programmer which is the bit that runs all the vacuum to operate the doors. 

I started reading the description and my brain just hit overload so I will have to try again later. Looking at the pictures which my brain is allowing right now those grey/white wires go through what they call a compressor cycling switch which says its on the cowl and cycles between -1C and +7.5C then into the module. Its grey/white in and out of that cycle switch so that should be easy to identify and maybe the easiest place to probe?  You could unplug that and connect your meter there.  I'm not sure what the signal is on this wire. Early in the description its just called signal.  They may explain it later but that was when my head started spinning.

The output of the module is a hot on a blue wire.  The other side of the clutch is a ground via low pressure switch.  On the EFI motor its a blue wire that splits to the clutch and fast idle solenoid. Other side of fast idle solenoid is direct to ground.

[smokuspollutus]

I have experienced this in various cars and the issue was 3/4 times the module and 1/4 times the control head.

The 1980 module will swap and work with a 1981 and should still retain the 1980 unique constant blower motor function. DO NOT install an 82-85 module (single wire ground) into an 80-81 (3 wire ground) or vice versa. I believe the only difference in the climate control system across powertrains in 1980 was the control head.

As TJ mentions, with some electronics knowledge, you can install a regular relay to cycle the compressor if you can't find a working module. That assumes the rest of the control system is working normally, which you should be able to determine with a factory manual.

[TJ Hopland]

Are the '3 wire' modules the one where the ground wire looks hacked in?  I kinda remember a friends 84 that had a wire just hanging out in that area that didn't look factory and was kinda melted that turned out to be what was keeping the blower from working.

There are external to the modules differences between the engines but I don't think there were indications of different modules at least in the electronic manual.  There could be different modules but they must have the same pinouts since there are no notes related to engines on the modules.

What it looks like which makes sense is the electronic climate control was designed for the DEFI because that option has the least amount of extra stuff.  The diesel and EFI have extra stuff that I presume the DEFI ECU handles with that system.