A/C cycles on by itself.

[BoostedEvIL]

Hi all,
I charged my A/c system today and now it seems to cycle on by itself. I noticed this today while I was resetting the IAC and TPS. During idle I can hear a loud click and then IACs double. The evap canister was soaking wet from condensation. RPMS also go up to around 950-975ish. It took me awhile to figure out it was the A/C doing this. I unhooked the compressor and this problem went away. Where do I start trouble shooting this? :nilly:
I got IACs down to 24 after I unhooked the compressor.

[Ts86ttype]

Do you have a manual A/C or an auto A/C climate control? Is it actually cycling on in the off position? Tom G.

[BoostedEvIL]

Do you have a manual A/C or an auto A/C climate control? Is it actually cycling on in the off position? Tom G.
Hi Tom.
Yep, The compressor cycles on by itself in the off position.(Not the blower, just the comressor.) My GN has manual A/C.

[Keller]

Did you fully suck the system down before you charged it? How much of what refrigerant was put in it? What were the pressures?

Chances are it is not yet full if it is short-cycling the compressor.

[Ts86ttype]

Some how power is getting to the LT. green wire that comes from the control head or maybe the LT. blue wire that comes out of the low pressure switch is getting power from some were??? When I look at the schematic for the A/C compressor to work, Power goes through the LT. Green wire to the lowside pressure switch, on the evap canister, then comes out the LT Blue wire to the A/C relay. The ECM turns on that relay and then power comes out the DR. Green wire to the A/C compressor. In the off position no power is suppose to be on that LT. Green wire. Are any of your wiring harnesses neer some heat and maybe have melted together??? Unplug the lowside preasure switch and put your test lite to the LT Green wire and see if you have power there when the control is in off... Let us know what you see... Tom G.

[BoostedEvIL]

Not sure Keller.
I had an A/C shop do it.
I was looking at it today and I found the plug on the back of the compressor was off. Looked at it and the pins were shorted together. I took out the shorting wires and it seem to idle fine now. I'm going to check the the IACs again later.

[Ts86ttype]

The switch on the back of the compressor is the high side preasure switch, they probably shorted it toghther to complete the ground circuit for the compressor clutch. It's suppose to be closed to make the compressor work and open when the pressure gets too high and shut off the compressor. That still doesn't tell you why the the compressor is coming on with your controls in the off position... The ECM not only can control the A/C on but it uses that imput from the control head to up the idle[IAC counts] to compensate for the load on the engine when the A/C is engaged. Still wondering why it is coming on??? Tom G.

[BoostedEvIL]

The switch on the back of the compressor is the high side preasure switch, they probably shorted it toghther to complete the ground circuit for the compressor clutch. It's suppose to be closed to make the compressor work and open when the pressure gets too high and shut off the compressor. That still doesn't tell you why the the compressor is coming on with your controls in the off position... The ECM not only can control the A/C on but it uses that imput from the control head to up the idle[IAC counts] to compensate for the load on the engine when the A/C is engaged. Still wondering why it is coming on??? Tom G.

I took it for a spin and the a/c didn't cycle on. temp got up to 190 and I let it idle for 5 minutes after that. I even turned the a/c on, but it blew hot air and I couldn't hear the compressor come on. I think the r-134 leaked out.

[Ts86ttype]

The plug in that you took the jumper wire out of, did you plug it back in to the switch on the back of the compressor? If you did and the compressor did not come on then you probably have a bad high side switch. Just put the jumper wire back in and see if the A/C compressor come on. Tom G.

[BoostedEvIL]

The plug in that you took the jumper wire out of, did you plug it back in to the switch on the back of the compressor? If you did and the compressor did not come on then you probably have a bad high side switch. Just put the jumper wire back in and see if the A/C compressor come on. Tom G.

Hey Tom,
I plugged the switch back in. Nothing... I took the car to the A/c shop today and got my money back. Turns out it leaked half a pound of R-134. They supposedly leaked checked it.
So I have a leak somewhere and a bad high pressure switch. Compressor did work good when it was full of r-134 though. I'll probably get around to looking for the leak later.
Thanks everybody.

[Ts86ttype]

Well keep us informed on what you find. I'm still wondering how the compressor was coming on when your switch was in the off postion??? Tom G.

[BoostedEvIL]

Hey guy's. I'm bringing up an old thread.
I'm going to finish off this a/c issue. I found the leak on accident. The canister nipple fitting had some debris stuck in it. So it leaked really slow. Its full of 134 now. But I do think that the high pressure switch is bad. Do I have to discharge the 134 to install my new high pressure switch. (The on on the line behind the compressor is the high switch right?)

[Keller]

Do I have to discharge the 134 to install my new high pressure switch.
You may not be a able to get the new one inserted with pressure still in the system. When you remove the switch, your system will begin to lose pressure, no matter what. Whether it loses all of it or not...guess that depends on if you could get the new switch inserted. I think it may be tough to do.

The right way would probably be to evacuate and recover the R134a, change the switch, suck the system down, and refill it.

I'm not an A/C expert, nor do I play one on TV... :stooges: But I did do my own conversion and have handled a few issues since.

[Ts86ttype]

The switch on the line behind the A/C compressor is the high pressure cooling fan switch, that has a three wire plug in... It can be taken off without any problem, there is a shrader valve under it and an o ring... A little R134 will seep as you take it off, but will stop... The Hi pressure switch is on the A/C compressor itself and has two wires to it... You have to evacuate the system to replace that one, it is under pressure... Tom G.

[Keller]

:doh: Must have misread that. For some reason I thought he was talking about the one in the compressor. Thanks for catching that, Tom!

[BoostedEvIL]

Well I finally swapped it out and nada. Must be the one one the compressor.

[Ts86ttype]

So now I take it that with your A/C fully charged that it will not work... If so then try unplugging the high side two wire switch at the compressor and jumper the wires together... That will complete the ground for the compressor... Also just for the heck of it make sure you haven't blown the 25 amp fuse for the A/C... Let us know what you find... Tom G.

[MikeRutledge]

Can anyone post a copy of the A/C schematic I am having some issues all around with a/c and the cooling fans I have the schematic for the cooling fans but one for the A/C would really be great also.