I was just wondering about my a/c compressor on my 93 FD. It currently doesn't work unless I connect a 12V source directly to the +power wire coming from the compressor. I figure this means I have a faulty wire leading to the ECU, but I was wondering if using a different ECU like the pettit unlimited which is what I switched to could cause this to happen? Also if it turns out I do have a bad wire in my harness would it be bad for to run a wire directly from the battery to keep it on when i'm traveling in hot weather? thankyou for your input.

 

could be low on charge check the low pressure switch.
btw do not run it low on charge it will damage the compressor.
matt

 

Sounds like it's low on charge and the low pressure switch isn't allowing the compressor clutch to kick on. Fairly common AC problem. Take it to a shop that does AC and have them check the system.

 

ok, i used one of those refill kits that has the pressure gauge on it to get psi reading of my A/C coolant. its currently at 146psi when the car is off. i don't know what the actually pressure is suposed to be at but that sounds hi to me. Do pressure switches ever stick or anything? I want to take the car to the shop as a last resport.

 

thats high enough that it should come on.
once it comes on then you watch to see how low the compressor will pull it down to.
matt

 

I need to make a correction on what the pressure is when both sides are equalized. I didn't let the car sit long enough to equal out. So it is 125psi. I wanted to check the pressure switch but i'm not sure where to find it or what it even looks like. I don't want to pressurize the system again unless it has enough juice in it as i don't want to damage it.

I'm going to unload the full story of my car. The A/C worked 2 years ago and then the engine died. Last fall I did a motor swap from a JDM car and I ended up using the JDM harness with a north american ECU (pettit unlimted) I used a different thread on this forum to get the ECU to work right with the JDM harness. Now the A/C doesn't work and I thought it might be a charge issue, and it still might be cause i don't know what the requried pressure is for the A/C unit to acctivate. I know the unit works if i unplug the A/C from the harness and jump that wire to a 12V source but then it doesn't cut out the way it should. So i figure this leaves three options for me. There must be a damaged wire on my harness(where ever the A/C wire goes) or it doesn't have enough pressure to allow the compressor to run, or the pressure switch is stuck in the power off possition.

I was trying to figure out where the wire went to in the wiring harness that the A/C connects to. I used an ohm meter on my old harness to try and figure it out but the only other wire that made i got power through was the wire that plugged into the water thermostat. That really confused me, i'm not even sure how the A/C system conects to the dash of the car now.

 

You need to get a wiring diagram of the AC system. That should give you some insight on how things work. I would say those pressures are enough to kick the switch on. I'd have to look at my notes for sure, but it usually doesn't take a whole lot of pressure to make the switch work.

 

ok, i got my a/c problems solved. Ive got it blowing pretty cold now. my pressure on the low side reaches about 35 to 38 psi. is this good or should i try to get it a bit lower?

Its kinda embarrassing but when I checked the fuse I must have pulled the wrong one out, i'm thinking the one beside the a/c fuse because it turned out the a/c fuse was gone. thankyou for eeryones help.

 

as long as its not cycling on and off it should be good
what did it drop to at 2500 to 3000 rpm's?
I cant remember now but I think the low switch opens at 30 psi or so
so if you rev it the low pressure switch might open the circuit

matt

 

when i turn on my a/c now, the clutch engages and builds pressure up for a little while, then it starts cycling on and off every few seconds(once pressure is built). Does this mean I have to much fluid in the a/c system cause I did add some in fluid. I always thought that a/c systems did cycle on and off just to maintain that pressure level. please let me know so i can adjust if needed. thanks.

 

sounds low it shouldnt cycle ever few seconds it should run till the temp sensor inside
the car turns it off, then it should be off for 30 to 40 sec. then back on for about the same
or longer depending on how hot the air going through the evap, is.
matt