QuestionQUESTION: I have a problem with the a/c on my '99 Ford Escort. IT was working fine and then it stopped. The clutch would not engage. I have observed the following white troubleshooting the system.
-Applying battery voltage via a jumper will make the clutch engage and supply cold air.
-A check with my simple gauge that came with the refrigerant refill indicates that pressure is in the good range when running.
-I have no voltage at the plug to the clutch unless I jumper the low pressure cut out switch.
-When I jumper the pressure switch plug, I get 12v at the plug with the heat/ac controls in the proper position but still no operation.
-I have a known good plug (the one I was using to apply batt voltage to the clutch) and when I splice it into the wires feeding the existing plug, the clutch will not engage.
I am baffled. Can you think of anything that I have missed or mis-interpreted? Thanks!
ANSWER: Steven,
Sounds like you have done this before, you basically jumped right to the point I was going to tell you to.
But I don't quite understand what you are telling me, let me say what I am understanding and you tell me if I am reading it right.
Your A/C clutch is not engaging. You have refrigerant inside the system. With the Key in the run position (engine on or off, doesn't matter) and you A/C switch on...
You bypass the low pressure switch with a jumper wire and your clutch engages? Or doesn't engage?
If you have refrigerant in the system and the clutch engages with the switch bypassed, that tells me that your low pressure switch is not closing the contacts as it should and needs to be replaced. This is a simple replacement, and a fairly cheap part (typically less than 20 dollars) To replace it, simply unscrew it from the hose or accumulator, wherever it is mounted, with a 1/2 or 9/16 wrench. Under this switch there is a schraeder valve that prevents the refrigerant from escaping when you disconnect it. tighten the new one down and plug it back in.
If it does not engage the compressor with the switch bypassed, and you for certain have 12 volts at the low pressure switch plug, that tells me the fault lies between it and the clutch. The next stop would be the high pressure switch. You can bypass this also with a jumper wire. Did your clutch engage? Yes? your high pressure switch is faulty and is opening the contacts when it is supposed to remain closed. Same thing replacing this as the low pressure switch. If your clutch did not engage... with the low pressure switch bypassed check your high pressure switch plug for 12 volts. No voltage? Do a continuity check on the wires connecting the high pressure switch to the low pressure switch, chances are you have a break in the wire. If you do read voltage at the high Press. switch plug... jump it and check the clutch hot wire for 12 volts. No voltage? do a continuity check between the wires connecting the high pressure switch and the clutch. Again... chances are you have a break in the line.
And if you have already ran a hot wire strainght from the battery to the clutch hot wire, you know that your clutch and ground is good.
I believe that you will find that your low pressure switch is the fault. This is the problem 7 out of 10 times. I hope I was of a little help, if you need more, or better clarification (I tend to get lost once I get to going) please do a follow-up onthis question and I will gladly do more.
Thank you for the question and good luck.
---------- FOLLOW-UP ----------
QUESTION: David, to clarify - with the low pressure switch bypassed, I get 12v @ the plug but the clutch still does not engage. I cannot explain that as when I apply voltage via a jumper to a spare plug I have, it works. When I use the spare plug spliced into the existing wiring with 12v read across the plug, it does not work. I jumpered the high pressure switch (all 4 wires) and still nothing although it did activate the cooling fan and step it up to high speed. I am still playing with it but for now have wired it through a toggle in the passenger compartment off of a spare fuse position because we are supposed to get into the 90's and I don't want to "melt". Thanks for the guidance and if you think of anything else I can look at, I would appreciate hearing from you again.
AnswerSteven,
We think alot alike. I had a '91 nissan. By the time I got done with it the dashboard looked like the cockpit of an airplane. I had everything ran by toggle switches. The more I look back on it, I am really lucky that thing even ran, and even luckier it didn't catch fire. But, it served me well for quite a while.
Now back to business...
You jump the low pressure switch... now are you saying you get 12v at the compressor plug and it doesn't engage? Then you splice in a spare compressor plug and the compressor clutch engages? Am I understanding this right?
If so... do you have a 2-wire plug to your compressor, or is it a single wire plug? If you have a 2 wire plug, then check the ground wire on the old compressor plug. It could be that it has a poor connection. Or the final point where the wire grounds to is loose or corroded. (Should be on the compressor or mounting bracket)
I do have to warn you about running the compressor and bypassing all the pressure switches, though. Those pressure switches prevent damage to your compressor itself. If it doesn't get disengaged in the event of low pressure it will cause the compressor to "burnout" as we call it. basically destroy it. And the high pressure switch more or less prevents pressure from continuing to build to the point that your hoses burst. If you are moving at a fair rate of speed or your cooling fan is switched also so that you have air continually blowing over your condensor you "should" (there's a dangerous word if ever there was one) be ok on your high side.
I want to continue working with you on this, I hate leaving you open, so if I am still thinking of the wrong spare plug you have worked into the system, let me know.
