I have a 1996 Ranger with a 2.3L 4-cylinder engine and five-speed manual transmission. The odometer stopped working a few years ago, but the engine probably has about 125,000 miles. Most of the time, the engine runs fine, idles nicely and the A/C is ice-cold. However, the idle occasionally either increases to about 2,000 rpm or it idles at normal speed, but surges slightly. While the idle problem is minor, it always causes the A/C clutch to shut off. The problem may continue for 10 minutes or a couple days. Then, all of a sudden, the idle smoothes out and the A/C come back to life.

If I understand the wiring of the A/C clutch, the idle issue is probably causing the PCM to send a signal to ground the power to the A/C clutch. Again, if I understand correctly, the power goes from the A/C control switch to the low-pressure cut-out switch, which is also the A/C cycling switch that controls the cycling of the A/C compressor. There are two wires that connect to the A/C cycling switch. The purple wire (I might have the color wrong since I am colorblind) has 12V, which I think comes from the control switch inside the cab. I connected a jumper wire from the other wire (dark green with a yellow stripe?) to the non-ground wire on the A/C compressor clutch. My rationale is that the compressor should still cycle based on the low-side pressure (vacuum?), but bypass the PCM. I have been driving the truck for a few weeks this way and the A/C works great and the engine is running well. I haven’t had the idle problem either, although I don’t know why this rewire would affect that problem. Since it is intermittent, maybe it is just a coincidence.

So what is the problem? I realize that I have bypassed the high pressure cut-out switch, which is a safety feature. How dangerous or potentially damaging is this? I have also read about a diode connected to the A/C clutch. I understand that it is to protect the alternator from an electrical pulse that can be generated by the magnetic fields of the A/C clutch. Have I bypassed the diode and what is the real risk to the alternator?

I really like the way the truck is running now, but I’d like to know if I have seriously compromised something with my rewiring.

Thanks,
David

 

Your explanation is mixing apples and lemons. There are two or three switches to the A/C clutch. High pressure, low pressure and wide open throttle switches in addition to the switch on the instrument panel.
The LPCO prevents the evaporator from icing. The HPCO prevents the compressor from overpressuring the system. The WOT prevents the clutch from engaging at Wide Open Throttle, allowing more power to accelerate.
Which did you jumper? The LPCO is on the accumulator, more or less just outside the evaporator plenum. The HPCO is on the compressor. The WOT is ??, possibly internal to the computer...
If you bypass the LPCO, you can cook your compressor, as it will be running w/o lubricant being flowed with the refrigerant. If you bypass the HPCO, you can blow up your system, at the weakest point.
I'd look at two things for what you describe. 1) engine grounds, 2)IAC - Idle Air Control - and 3)TPS - throttle position sensor. Pull your codes to see if there are any failures noted.
tom

 

Hi Tom,

Thanks for taking time to reply to my question.

I connected the jumper from the LPCO switch to the A/C clutch. I was driving the truck today and it is clear that the compressor is cycling on and off based on the temperature of the air coming out of the vents. If I turn the A/C off using the main control inside the cab, the compressor clutch switches off.

I have recently replaced the IAC and TPS, but the problem still persists. I have had the codes checked, but there are none (check engine light is off). I've taken it to a shop that I have used for more than 15 years. The tech is one of the best I've ever known, but he cannot replicate the problem since it just comes and goes.

I realize I have bypassed the WOT cut-out, but I rarely hit the gas that hard in this truck. I also realize that I have bypassed the HPCO and might damage the system, but I am on borrowed time since the A/C is 12 years old. Here in South Florida, the A/C runs nearly year round and the A/C guys tell me a compressor usually only lasts about 5 years. It doesn't seem like a vacuum leak or related problem since most of the time the engine runs great.

Have I missed something obvious?

Thanks,
David