The AC in my truck isn't working and I don't think its worked in quite a while. The compressor clutch doesn't engage. I pulled the plug on the wires running to the clutch, and had 12 volts at one and nothing on the other. All fuses are good. Where do I start looking? Can I just run 12 volts to the wire without power to see if the clutch is good, and the compressor works?

 

the side with nothing on it needs to be grounded to complete the circuit.

 

So, is there some switch that grounds that is supposed to ground that circuit? Obviously I can ground it to test the clutch, I'm just wandering because I checked it for continuity to ground and it was open.

 

well there would be a pressure switch in the low side at least. looking at a diagram for a 91.5 shows the low pressure switch and an electronic clutch cycling switch, which I think Jim Lane had a write up to replace that with a relay.

Not sure how a 90 is wired up though.

 

i dont have a wiring diagram in front of me but i am a a/c tech.

usually the clutches are one wire 12/24 volt and then the clutch is grounded to the compressor case .

the clutch is the last thing in the series circuit that makes the a/c work
1st on/off
2ndthermostat
3rd binary pressure switch ie low pressure and high pressure cut out
4th the clutch

if you have 12volts at clutch and no ground at the plug you have a GROUND issue

 

The compressor clutch on a first gen is switched on the ground side not like the normal single wire clutch you are thinking of Lucas. The computer switches ground and the clutch has power all the time. Unless a non ic is different from an ic truck.

 

cool good to know..

not to common.. kinda like a british car.


i have never had to even look at mine its r12 and blows cold,,lol.iam a refrig. tech and ive never needed to check this truck in the three years ive had it

 

You are probably just low on charge, the low pressure cutout prevents the compressor from running to protect the compressor because the oil is carried in the refrigerant charge.

Follow the refrigerant lines back to the H-valve and disconnect the connector from the low pressure cutout switch, then jumper the terminals using a unbent paper clip, this should allow the compressor to start, then check your sight glass on top of the receiver drier, you might have a piece of tape over the glass if you cannot find it.

Now you will have to figure out you are going to do for a refrigerant.

Some vehicles also might have an ambient temperature switch in the circuit but not on out trucks

Jim

 

Couldn't imagine us here talking about our lorries with our heads under the bonnet checking the mains from the accumulator

I have had my share of trying to figure out the British automotive terminology.

http://lotus-europa.com/manuals/misc...erminology.htm

Jim

 

As for filling, I saw some stuff online called Duracool R12A. Claims to cool 12 or 13 degrees cooler than than R134A. Reasonably priced, too. Will work with either style of system.

 

I grounded the compressor and sure enough the clutch works and the compressor turns. System is really low on charge though... Now I've got to figure out what I'm going to do there. I hear some of these R12 replacements are snake oil. Can anyone personally vouch for one?

 

I have freeze 12 in mine and it blows icicles, don't know about the rest...Mark

 

There's a whole other thread on use of propane as a refrigerant, some for, some against. My AC was pretty lame so I topped up with propane, not very much but just until my sight glass showed some turbulence. My AC is now quite satisfactory, not COLD as some report but pretty much how I like it. Now I can't wait 'til SWMBO says it's too warm as we steam thru Saskatchewan later this month.