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'99 Ranger 4.0 Air Won't Kick On unless wiring a jump


NoHandlebars

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Ok here is the deal. I have completely ran out of ideas.

So last year my air worked just fine, ok. This year I turn the A/C on from inside the truck and, well nothing. We get the auto kick on and off of the compressor when you start the truck, but that is it.

So we have tried jumping the high, and low pressure sensors, both together and individually. We checked all the wires and the correct power is getting to them. It has freon in it. We jumped the compressor with the air turned "on" in the truck before blowing a fuse and the clutch engaged while being jumped, and when we checked inside the truck it was blowing cold AC no problem. So we know the compressor works. The wires to the compressor also have power going to them. We have literally jumped/tried everything we can think of, we even changed the orifice filter.

Has anyone else had this problem? It has me and 3 other people totally lost here. :shout:

Basically. The air works if I jump the compressor. If I turn it on normally, it will not kick on. All wires, connections, etc. have been checked and work.
 
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Earl43P

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Replace the cycling switch!
Refrigerant will NOT leak out when you change it either.

It's a cheap part.

Another possibility is that the air gap in the clutch is too great.
You can shim its fingers with some twists of wire to close up the air gap.

You should try that first, since it's free.
Or do it correctly, http://www.autoacforum.com/messageview.cfm?catid=2&threadid=17015

Welcome to The Ranger Station.
 

NoHandlebars

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It is neither of those. Every switch/sensor is getting power. The cycling switch is new. Clutch and AC works just fine when we jump it directly to the battery. Has freon. The clutch turns on and cycles when you start the truck like it is supposed to but that is it. When you turn the AC on from inside the truck nothing happens.
 

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Alright everyone. I figured it out. So after many hours of following wires and checking stuff.

It is actually the PCM causing this. I pulled the relay off and jumped it with some wires and the compressor kicked on. Double checked the relay and it was good. Followed the p/y wire to the pcm and checked that, was also good. Basically followed and checked every wire with the AC system. Right now have wires in relay spots, wired to inside the truck for temporary air. Cycling it manually. Waiting on new PCM to confirm problem.
 

Earl43P

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Ummmm, the way it looks to me, if you CUT the P/Y wire, the PCM CAN'T (supply the ground to) energize the WOT relay and AC should operate (but won't cut off the compressor when you floor the gas).

I'm looking at the 2000 EVTM, which should be the same as your 99.

I'd be happy to send that to you if you PM me your email address.

My puzzlement is that you say power is everywhere it should be. "The wires to the compressor also have power going to them." <If that were true, the compressor clutch would be engaging. The only way the PCM can kill that is using the WOT AC Control relay.

Power on the VT wire tells the PCM you want AC on.
PCM looks for the ground supplied by the AC Cycling Switch (which you could have jumpered) and the High Pressure cut off switch. So, if both of those switches prove out, the 12v on the PK/LB wire from the fuse goes straight to the WOT relay contacts, which should be closed unless:

TPS says the gas pedal is floored
Temp is below 32 degrees or so (IAT signal, IIRC)
AC function not selected (HVAC Control in Off)

You should have 12v on the Red wire from PCM Pin 71 to the WOT/AC Control relay.
All the PCM can do is GIVE or take away the ground provided by the PK/YE wire from PCM Pin 69.

Earl has serious doubt that your PCM is bad.


Humor me: Take your Voltmeter and set it to Ohms. (touch the meter leads together and see 0 ohms) Disconnect the PCM and probe Pin 66 BK/YE wire's pin (harness side) and touch the other lead to ground. If you don't get continuity (use the tone feature or look for ~0 ohms, just like when you touched both meter leads together). If you don't get continuity to ground either the cycling switch is bad or the high pressure switch is bad. Both of those switches should be closed contacts.

Your method to jumper the WOT relay contacts doesn't convince me of a bad PCM. All you did was take away the PCM's ability to turn off the clutch, which it is clearly doing. That fact tends to make me believe the PCM is GOOD, it IS turning off the compressor, which it uses logic circuitry to DO. It's DOING that.

I've serviced and worked on quite a few Ford Air Conditioner systems. Found a few bad cycling switches, leaks, air gapped too far clutches (worn out) and Black Death clogged orifice screens. Haven't encountered a single PCM failure in a lot of years of servicing AC's for beer $.

I think this schematic will help you. See Page: 54-2
 


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