How to troubleshoot A/C probs?

[Phaedras]

I've been having issues lately where my AC will decide to work for a week, then conk out for another 2 weeks. I hit the button and nothing but regular air comes out of the vents. Usually I will see a very minimal drop in RPMs at idle, but not the usual major drop and engine noise sounding like it's cursing you for putting it through the additional strain.

 

So where should I start poking with the multimeter to trace the root of the problem? I know I have enough R12 (had it checked) and it doesnt seem like the compressor is shot (but who knows), after all, every once in a while it'll feel like kicking in for a few days.

[86subaru]

maybe check ac relay ,on my 86 sedan it was on the passanger side under the hood

[subynut]

Same here. Mine will run for a time then kick out till I switch to somthing differant then go back. What gives?

[Phaedras]

maybe check ac relay ,on my 86 sedan it was on the passanger side under the hood

 

How do I check it? Just see if there's any voltage at all, or do I need to look for a specific type of resistance?

 

And how do I tell if the compressor is shot?

[NorthWet]

You can run power to the compresor clutch and see if it turns on... but this will really only test the clutch electricals, the compressor mechanicals, and let you tell if the system has adequate refrigerant. Be careful not to run it for moe than a minute or so unless you can confirm that it has adequate refrigerant (i.e - check the siteglass, check temp coming out of vents).

[azsubaru]

I'm currently working on my own AC problem with my 91 Loyale. I haven't fixed it yet, but I've tracked the circuit partially. At least on my 91, there's a 15 amp fuse for the AC over on the top rear of the passenger side wheel well, and mounted in that same area, kind of tucked behind/under the same mount, are two relays. At least one of them turns the AC compressor on, and I'm not sure that both aren't involved in the whole circuit. The relays are identical, so you could switch the plugs on them to see if there's a change in the symptoms.

[Roundeye]

You really need to put gages on it. You should see around 28 on the low side and around 250 on the high side. What pressures you see can tell you a whole lot.

 

Without knowing what your pressures are, some possible causes could be: 1. Moisture in the system causing icing in the line(s) and/or components. If this is happening, you will see ice form on the outside of the line where the restriction is. 2. Your clutch could be slipping causing the system to kick itself off. (Hitachi system) Make sure your pickup coil air gap is adjusted correctly (it's the small black box with 2 wires going to it that is mounted over the pulley of the compressor). If it kicks off because of this, you can turn A/C off for about 3 seconds and then back on again and it will start working again. 3. Your expansion valve could be sticking (most likely from what you describe). It's mounted in with the evaporator. System discharge and evaporator removal required to change it....good time to convert to R134.

 

Try to find out what your pressures are and post them here. Include the outside air temp at time of readings too. Myself or someone else can help you alot more with that info.

[idosubaru]

you said it was checked, did you verify it doesn't have too much refrigerant in the lines? this can cause your problems as well.

[Phaedras]

You can run power to the compresor clutch and see if it turns on...

 

How do I accomplish this?

[subynut]

I'm not sure whitch A/C unit you have but if it's the Hitachi, there are three wires that goto the the unit. There's one blue wire that goes to the compressor clutch and the other two goto the pickup coil. You want the single blue wire. Give it switched +12V. But, like NorthWet said, make sure it has adequite refrigrant and that it's accually cooling the air. You don't want to fry somthing, ya know?

[Phaedras]

Well I got a cheap bar-type guage and it seems that with the engine on as well as off I'm getting a solid 90 psi on both sides. Isn't that a bit high? But even if, why was the AC working for months beforehand?

[Phaedras]

Bump. Dammit, it was working for 2-3 days and now it's crapped out again. Any more suggestions?

 

It's summer in Florida, this sucks...

[erik litchy]

Same here. Mine will run for a time then kick out till I switch to somthing differant then go back. What gives?

 

thats what mine does. but only on the highway. around town its fine. its got a good charge too

[Cougar]

You both may be having trouble with the vent doors. They are controlled by vacuum and there may be a leak that is causing a problem. Especially if the problem happens while driving fast, making the throttle open more and creating less vacuum.

[Phaedras]

You both may be having trouble with the vent doors. They are controlled by vacuum and there may be a leak that is causing a problem. Especially if the problem happens while driving fast, making the throttle open more and creating less vacuum.

 

How and where would I check for these leaks? Also, speed seems to not be the issue. I do however every once and a while think that it kicks in for a split second, then dies. This is at a cold start. It will smell a bit like A/C for about 1-2 second and then goes back to regular outside air.

[erik litchy]

You both may be having trouble with the vent doors. They are controlled by vacuum and there may be a leak that is causing a problem. Especially if the problem happens while driving fast, making the throttle open more and creating less vacuum.

 

sounds logical but the compressor is turning off. (easy to tell by the engine performance) the air comes out the same temp as the outside air, so its not going through the heater.

[subynut]

You both may be having trouble with the vent doors. They are controlled by vacuum and there may be a leak that is causing a problem. Especially if the problem happens while driving fast, making the throttle open more and creating less vacuum.

Don't think so, it's more like the compressor kicks on for a time then quits. After I converted to SPFI, it seems to stay on when it's supposed to. I wonder if the idle was too low with the carby that caused the pulser to say the compressor is spinnung too slow and kicks it off. That problem seems to have fixed itself for now. Now, if I could only get the coolant temp down to a reasonable level. With temps in the high 90s, the A/C on, and city driving that temp goes from 215 on up to 240+ even tho both fans are running. I think it would keep climbing if I don't kick the A/C back off and let her sit in the shade and idle for about 5 mins then I'm back to the normal 215. But that's another topic to discuss.

[Cougar]

Well you both should check the power to the compressor. There is a relay and fuse mounted on the right hand strut tower. There may be a problem with the relay.