Hey, I put HBHRacing in the title because Ive seen some of your responses, and see you KNOW what your talking about.

I had a locked up compressor and replaced it last week. The system was still full, the compressor just locked up and the clutch started slipping. Everything worked great prior to this.

Before I found the locked up compressor, I tried jumping the cycling switch, knowing that the system was full. Its that 3 wire swith, and I know I shouldnt have messed with it.

Anyway, I evacuated the system, replaced the compressor, pulled a vacuum for 20 min, then started the car and started putting in fresh 134a. The compressor never turned on. After troubleshooting for a bit, I just pulled the relay and jumped it to run the compressor. I then filled up the system and it was blowing good and cold.

I pulled out my jumper wire and put the relay back in and nothing
I have 12VDC going to the coil, but when I plug in the relay the voltage goes away.

Im assuming when I jumped the cycling switch, i messed it up. I dont have a wiring diagram, but Im assuming that that switch is what powers the compressor relay. Am I right? I just dont want to put on a $40 swith, and find out its a different problem.

Edit: just found this on shoebox's website http://shbox.com/1/hvac_compressor_control.jpg Looks like all that crap is contolled by the ecm too. Im hoping its the switch.

 

on a 95, that switch is a pressure sensor that feeds to the PCM, it is the PCM that works the compressor, everything else is a a/c request signal

sorry, no other help

 

Yea, I just noticed that. Looks like that switch sends 5v to the ecm. Its all solid state from there. I probably just messed up the switch, but dont want to replace it till I know thats the problem.

 

if you have access to a scanner, see if the PCM IS GETTING THE A/C REQUEST FROM THE A/C CONTROLS, AND SEE WHAT IT THINKS A/C PRESSURE IS, IT IS PROBABLY PEGGED HI OR LOW



danm caps lock

 

Thats a good idea. I dont have access to a scanner, but do have a scanmaster. I think it gives ac pressure. Im gonna go check it out...

 

Ok, I just checked out the scanmaster. Its reading .26 for the AC pressure. It looks like its not reading any pressure. I guess its probably the pressure switch then

I also had some AC realated codes, lol:

61 A/C system performance
66 A/C refrigerant pressure sensor circuit (open or shorted)
67 A/C refrigerant pressure sensor circuit (pressure sensor or A/C clutch circuit problem)
68 A/C relay circuit (shorted circuit)
70 A/C clutch relay driver circuit

Looks like the ecm thinks the sensor is shorted because of the low reading. The other codes probably came from me pulling the relay, and jumping the normaly open contacts to run the compressor.

 

ok. lets get a starting point..

first off. the compressor locked up and didn;t move anymore correct?

all you replaced was the compressor?

if so your going to run into some trouble. All thatmetal shavings from the compressor going bad are in the whole system and must be removed. at the least the drier, compressor and H valve shold ahve been replaced and the condensor and Evap core should ahve been throughly flushed... and then flushed more..


and then flushed again

the problm is that all that trash will end up back in the new compressor and eat it up yet again. if you did all this good. if you didn;t then just use it till it blows.

ok. now. for the electrical issue.. clear all the codes out. lets start at the pressure sensor. check for ground at the black wire, 5 volts at the grey wire.... make sure you have that. if not lemme know.

at the relay with the key on. check for hot signals on 2 of the termonals. you should also have ground on one of the other termonals. now.. turn the ac on and start teh car. you should now have another ground signal at the final termonal. lemme know what your missing.
anothing simple thing is to make sure that you have ground on the black wire at the compressor

now, a lot of times any time you disturb that pressure sensor it can go bad. if your lacking the ground signal at the relay when you turn the AC on you can try to jump the switch connector making sure that you jump the red wire to the grey wire.


Lets start with that and see what we can get

 

Yea, the compressor locked up, and I replaced it. I didnt flush the system, although I probably should have. I guess if I have problems again I'll do a more thurough job.

I'll check what Im getting at the sensor tomorrow. At the relay, I have the 2 hot terminals. I guess I have a problem with the ground that goes to the coil when I plug the relay in. I have 12VDC there, but when I plug the relay in, it goes away. I'll also try jumping the red wire to the grey wire and see if everything works. If it does, I guess the switch failed when I messed with it.

Hopefully everything will last since I didnt flush it. The oil in the compressor didnt look bad or anything, so hopefully it didnt circulate crap throughout the system.

 

I have ground at the black, 5 VDC at the grey. I have 2 hots and 2 grounds at the relay.

I jumped the red and grey and the fans kicked on, but not the compressor. What does this mean?

If I jump the normally open contacts of the relay, the compressor kicks on and it blowes ice cold.

Are there any resistance tables for the pressure sensor?

 

lemme just make sure. at the relay you have 2 hots and one ground. then when you activate the AC you have another ground?

if so.. make sure that the relay isn't sticking, just swap with with abother one...

but then unplug the connector at the compressor, hook everything up and turn it all on.. then see if you have hot on one side and ground on the other.

 

Yes, 2 hots, 2 grounds. BUT, like I said in the first post, when I plug the relay in, the coil voltage dissapears. So, whatever controlls the coil is messing up. The wiring and compressor are good. No need to check voltage at the compressor, because when I jump the NO contacts of the relay, everything works. The problem is the coil voltage drops out with the relay in.

 

I just wanna make sure that you on;y have 1 ground normal and then the other one shows up when you trun the AC on. you might need a relay.. if you have all the imputs but when you plug the relay in you lose voltage thats probably it

 

Its not the relay. Ive switched them all around, and they all work. I know quite a bit about electricity and control circuits. Its not the relay. If the relay were bad, the voltage would not dissapear when I plug it in. Whatever supplies the power to the relay coil is the problem.

It took about a 1/2 hr to figure out what the hell was going on. When I jump the NO contacts, the compressor works. I have coil voltage. The relay is good. Whats going on here, lol. Damn thing made no since, and fustrated me. Then I finally left the meter on the coil voltage when I plugged the relay in. The voltage goes away.

So the question Ive been after is: What swithes the ground on/off to power the relay? The problem is either in the ecm, or the pressure switch. Im guessing its the switch since my scanmaster is showing such a low refrigerant pressure, and I have the ground and 5V at the switch.

 

ok. lemme tel you how the system work..


you have constant ground to the feild coil of the compressor. 2 hot feeds to the relay (one for the relay coil and one for the leg) you have the AC switch inside that has a hot feed, when you turn the **** to any AC posistion the path to hot is made. this is the AC requst signal to the pcm. when there the PCM looks for the correct signal from the pressure switch. an if normal the PCM will send a ground signal to the other side of the relay coil which closes the relay and sends power from the hot leg out to the other side of the compressor feield coil.

if you have all the signals untill you plug the relay in. I would sugest taking a little wire and some spade connectors and extending the relay so that you can porbe the wires while the relay is pluged in and see what ecactly your losing. but honestly if you have all the feeds with the relay out they should remain there with the relay in.


The only other parts of the system..

there is a temp prob on the evap core but I have yet to see one fail. There is also a diode in the connector near the compressor. I'm still waiting for someone to give me a satisfactor answer as to why it's there but no one has yet.

 

I tried that today. I can plug all of them in eccept the coil ground. When I plug it in, the ground goes away. So I measure resistance to ground. I get something crazy like 2.5 mega ohlms. That wont power anything. So I leave all the wires hooked up, then jump the NO contacts. The compressor turns on. I remove the jumper, and the compressor stays on I dont know what that did, but it fixed it. Everything works normal now Turns on and off when I turn the ac on and off.

So, about that whole flushing thing. How do I go about doing this? Remove the lines and use a pressure washer to flush the system one componant at a time (excluding the compressor)? Since the day I filled it up, I may have lost a little pressure. I filled it up again, now Im only blowing 70*. It was probably 55* right after the swap. Im assuming that the evaporator or something is plugged up with metal now I cant win