AC compressor clutch not engaging

[da_reeseboy]

I just am hoping for a little confirmation I guess on my thinking here before I go spending money...

My a/c has started acting up as of this last weekend, blowing warm air. Every now and then I get cold air and its nice and frosty when it works. In my quick diagnosing I've found that the relay is being triggered and it seems to be fine, but the compressor clutch doesn't engage. To be sure, I pulled out the relay and stuffed a jumper wire in there - still no clutch engagement. Then, with the jumper still in, I pulled the plug off the compressor and checked for voltage on the black/white wire (I believe this is the right one) and had 13v.

My understanding is that if I had a sensor flagging an issue in the system then the relay wouldn't kick, right? Or is there another sensor that wouldn't allow the compressor clutch to engage after the relay?

 

[SICK SOCIETY DSM90]

I have a question about your ac system is it full with no leaks at all? sounds like your system is low and needs to be charged and may have a leak. How old is the compressor ? has it ever been rebuilt. Just sounds along those lines rather then a electrical problem. When I was working on cars in school we had some that would kick cold and the compressor kicks on then after a few seconds of cold air the compressor would disengage. as soon as you charged system full was good to go. if you can get it emptied and pull a vacuum on the system to check for leaks and another visual inspections you can look for oily spots around ac compressor bolt and around the system. its either a leak or low Freon levels. let us know what you come up with. I will help if I can I am still a new mechanic but I can point you in somewhat the right direction.

 

[da_reeseboy]

Thats the thing, why I posted this. The compressor relay is "clicking" and staying engaged, so I don't think its low or that wouldn't happen. And even if it wasn't clicking (which I'd think would mean low levels) by bypassing the relay and using a jumper the compressor clutch should have engaged. I confirmed that 13v is getting to the compressor clutch, its just not engaging.

As far as the age of the compressor goes, its the one that was on the car when I bought it in 06, so who knows...

 

[SICK SOCIETY DSM90]

Hmm that's weird if your getting signal from relay to come on and its getting the power source it should work if the system is charged. My best guess would be try a new compressor that you know works and see if that fixes the problem. sometimes what we do is get a relay you know works and put it in sometimes jumper wires do not always give you the best results. just seems if you bypassed the relay and the voltage is right at the compressor I would probally think the compressor is bad. Let me know what you think these are just educated guess from what I learned in school and life experiences around cars. very interesting problem like to see what fixes it.

 

[da_reeseboy]

Thats what I'm thinking too. I did finally run a jumper wire from the battery positive straight to the pin that the black/white wire connects to and still no compressor clutch engagement. The only 2 things that are still questions in my head are:
1. Is the black/white wire the correct wire at the A/C compressor?
2. Is there a safety in the compressor that won't allow it to engage even if power is delivered on the black/white wire?

That compressor is a PITA to replace from what I've read so I'd like to confirm those things before I dig into it.

 

[1995silvergst]

Download the factory service manual, you will need section 55 pages 1-52 for a/c. I would test the clutch and if it passes put a set of gauges on it cause it sounds like the compressor is shot.

 

[SICK SOCIETY DSM90]

Ya sounds like the compressor is the issue and the only ways for the compressor will not engage is if the clutch is messed up or low charge or no charge which with guages you would be able to tell without adding refrigerant. hope we get this problem fixed it does get pricey with ac work but there is a solution for that roll windows down and get rid of ac all together .

 

[1995silvergst]

GA much like Florida gets hot! And A/C doesn't have to be expensive but most shops replace parts until it works which is very expensive. Download the FSM and follow the tests diagnose it properly and it will save you a ton! With a set of gauges and knowledge of what the high pressure and low pressure sides are doing you can definately diagnose the compressor good or bad.

 

[SICK SOCIETY DSM90]

Ya i agree i am in texas and do not have ac in my car gets pretty hot. Ya see the shop i work at we do not just replace one part we replace the whole thing which is pricey its the only way we can warranty the work. But on the side i have do my own work and usually there are high and low side pressure reading diaghrams online and a set of guages and you will be good to go. if not take it to a shop to diagnose the problem.

 

[Lou98GSX]

you have power make sure your ground is also good

 

[da_reeseboy]

Thank you for the responses, I will report back as I test things.

 

[95blackGsTurbo]

If you are getting power and ground then the problem is in the A/C clutch, if you have power and no ground, check the ground side circuit. There is a freeze-up switch on the evaporator core that has a connector located behind the glovebox. Unplug it and and jump the ground pins on that and see if that fixes it. Very common problem but the part isn't really available anymore. Outside of that you really should have A/C gauges on the car before doing any work to see if the system even has proper pressure.

 

[da_reeseboy]

To confirm things today I tested the clutch per the FSM - connect the compressor housing to ground, connect 12v to the clutch wire.

No click so it must be bad.

 

[1995silvergst]

That is good news and not too difficult to change out. When replaced then with gauges test the pressures to check the effectiveness of the compressor when cycling correctly.

 

[SICK SOCIETY DSM90]

Sweet! ya i have rebuild a clutch before not to bad. Do that and proper charge you will be set. if at all possible get a vacum pulled becuase if you happen to have a leak you will waste time and money. I know no one likes losing money. Just some food for thought

 

[da_reeseboy]

I thought I would give something of an update -
My A/C started to work yesterday out of the blue. When I got home I hooked a multitester to the clutch. When it wasn't working I was getting around 5K ohms of resistance, now that its working its around 4 ohms... definitely a short, probably in the clutch coil.