I have a 1995 Ford Windstar. When I turn on the air conditioning, the compressor clutch does not engage despite having sufficient refrigerant in the system. Jumping current directly to the compressor clutch will engage the clutch, so it’s not the clutch. I suspect the relay for the compressor clutch inside the CCRM may be bad, but am not sure how to test it. I have a Haynes repair manual, but it is of little help. Does anybody out there know how to test this device?
I would start by checking the low pressure switch.
The switch should normally be closed with the system off, correct?
If the system pressure is ok then the low pressure switch should be closed.
If system pressure and the LP switch is fine you might consider a problem with the CCRM.
The relays in there are heavy duty Bosch 40 amp relays and they seldom fail. What might be happening is a faulty connection in the wire connector that attaches to the CCRM.
Does the CCRM have the little 8MM bolt head on it? If so, loosen that about 3 or 4 turns and try wiggling the wire connector with the engine running and A/C on. Note if you hear the compressor kick on. If you do, the problem is likely in the wire connector plug. The relays are heavy duty but the wiring and pins are somewhat small and delicate.
I had issues with this a few times on my old Sable; once with the fuel pump output lead and another time with the compressor pin. Hope that helps.
The low pressure switch should be closed with sufficient pressure in the system. It opens when the pressure drops too far. It doesn’t care if the A/C is on or off.
I tested the switch on the low side, and it is open. I tried running the air conditioning and the engine while jumping the two wires on the harness. This caused the cooling fans to kick on, but the compressor clutch did not engage. The switch on the high side has four pins, and there is no information in the repair manual about this switch.
On another note, I said in my original post that there is sufficient refrigerant in the system. I do not have an a/c machine or manifold gauges and am trusting the instructions on a store bought recharge kit, so there may well be insufficient refrigerant or pressure in the system if these things are not to be trusted. It has been a long time since I have done a/c work and my memory has gone fuzzy. The instructions said to charge the system until the low side pressure was at 35 psi with ambient air temps at 65 degrees, which it was at the time I tried charging the system with this kit. Does this sound right? Sounds kind of low to me.
The four wire switch on the high side I think is a combination high psi cut out, and a loss of charge low psi switch. It maybe time to take it to a A/C shop. If the system was completely flat it will require specialized equipment to find and repair a leak, driers need replaced, and system needs evacuated. Plus you could hurt yourself if you are not properly trained.
This is hard for me to figure without a schematic. I have a stack of Ford schematics but nothing for a Windstar.
Is that 35 PSI static pressure; as in engine off, A/C off, etc.? If it is then that’s way too low and it should be up in the 115ish range.
With engine running, compressor engaged, etc. then 35 is about the borderline point near as I can remember for compressor engagement and disengagement.
With the low pressure switch jumped and fans running you might consider tapping briskly on the CCRM and wire connector with a screwdriver handle to see if the compressor kicks in and out.
I’ll see if I can fish around for a schematic on this thing because I never liked messing with electrical stuff without seeing how it’s laid out first.
The 35 psi is a static reading, since the compressor will not kick on. It would not surprise me at all if this is a case of the system simply being empty due to a leak. I have had the van for about five months and was told when I bought it that the a/c did not work, but had in the past. It’s been so long since I’ve dealt with a/c work that my memory is fuzzy and the more I recollect, the more it points to a likely case of a significant leak and too low system pressure to activate anything. I may end up just taking it to a shop and having it evacuated and recharged and see what happens.
35 psi sounds right with the system running. The high side should be more like 270 psi.
But, since the compressor is not running, 35 is way too low for equalized pressure. The equalized pressure should be more like 120 psi.
Unfortunately (b/c I hate getting to where I’m at the mercy of the shops) taking it in is probably your best bet now. As noted, the low side should be somewhere in the 30-40psi range with the compressor running, but up at around 120-ish without. So if you’re determined to have the AC you need somebody with the equipment to evacuate, check for leaks & recharge.
At a static 35 PSI reading this would mean the system is way undercharged. Both high and low sides will stabilize when the engine and A/C are off and while it will vary a bit the general rule of thumb is about 115-120 PSI on both sides.
I could not find a schematic for a Windstar but did look at some a Taurus. Odds are the wiring is similar. The compressor relay is one of 5 in the CCRM and while 4 of them are mechanical point relays the compressor relay is solid state.
Basically, it’s 3 wires with one going to the compressor clutch and the other 2 going to the ECM with one of those 2 going through a pressure switch.
At this point though it sounds like an undercharge in the system and given the age of the vehicle it’s likely due to a compressor shaft seal leak. You could try charging it with one of those all-in-one cans of refrigerant/oil/stop leak.
While I’m not a fan of stop leak products this can actually work or even buy you some time.
A few years back I was developing a leak in my old Lincoln. (About a can a year)
After adding a can of the above it slowed the leak down to about 1/4 can a year.
(The compressor was buried deep and I was busy so I took the easy way out with a prayer.) 
In addition to a compressor shaft seal, I wouldn’t doubt it if some of the lines themselves are leaking. This vehicle has some steel a/c lines, and they are pretty rusty. I will probably try charging it with the DIY cans of all in one refrigerant to see how that works out. If it leaks out quickly, I will probably change out the steel lines, receiver/drier, and orifice tube and try again. I have come to like my a/c in the summer time and have been spoiled by my rusted out old Buick, which I have had for six years and never had to touch the air conditioning system except for changing the compressor drive belt a couple times over the years. That system still has R12 in it and blows cold enough to hang meat in the car.