Wiring question for a/c | Ford Escort Owners Association (FEOA)
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Wiring question for a/c

Discussion in 'ZX2 1998-2004 2.0L DOHC' started by jayandgee, May 26, 2010.

  1. jayandgee

    jayandgee New Member

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    Hi all! I have a 99 Escort ZX2 with non-functional a/c. I found the a/c relay was bad (melted with a burned-out spot on the circuit board) in the CCRM, and I tried to solder in a new relay. In the process I messed the circuit board up. So I removed the new relay, and I'm just running the car without that one. I'm pretty handy with wiring in relays, and I'm now interested in just wiring in a toggle switch and relay to kick on the a/c when I want it on.

    I would really like to just be able to signal the ccrm to kick the a/c on with an external relay, but I’m not quite sure how to do it. Since the system monitors a/c pressure and adjusts the hi/lo cooling fan setting (and WOT state as well) I'd like to just have the system control everything like it's supposed to. Is there a way to do that?

    Plan B is to just install a relay to kick the a/c compressor in with a toggle switch and another relay to kick the cooling fan on high when ever I turn the a/c on. I'm not sure if this is a good idea. I would include the high and low pressure a/c switches in my circuit. I'm not certain that it's safe to just run power to the cooling fan's wire for high speed without some sort of diode. Not to mention that I recall reading somewhere that the high pressure switch isn't really a switch, but some sort of rheostat that signals the computer with the a/c system's pressure.

    What do you all suggest? I've looked at the local salvage yard for another CCRM (That I can fix if it needs it.... now that I know of a better way to desolder). They don't have one with matching numbers. I know I'm not paying $220 for another ccrm from Ford. I really would appreciate some advice. Some of the threads on this site show how to wire in an external relay, but it seems like that way would just make the a/c system always be on and running. And I’m not sure it would activate the cooling fan either.

    Thanks for any help you can offer.

    I'm interested in the wire diagram for the 2-speed cooling fan, as well as for the pressure switches / rheostat on the a/c system. I have a nice diagram for the CCRM, but nothing that shows me what each relay does; particularly what each pin on the relays is for.
  2. jayandgee

    jayandgee New Member

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    I've gone through the 'how to' thread for ccrm repair.... good stuff! I'll tinker around and see what I come up with. I wonder if I can still just hook up the system to relays: one to control the a/c compressor and signal the second to close the switch on the high speed for the cooling fan.
  3. homestead367

    homestead367 New Member

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    You might be able too. I can tell you one thing I have learned since i have been fighting to get my ac to work for 3 years now. Part of the relay is used to shut the compressor down when you are at WOT so you don't blow the compressor up. Just remember that.
  4. madmatt2024

    madmatt2024 FEOA Member

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    You do need to have the relay or the compressor won't be able to shut down if pressure gets too high or too low.
  5. ISU_Alex

    ISU_Alex New Member

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    Wow, I am in EXACTLY the same situation. First time the A/C crapped out I soldered in a new relay and it worked, but the board was in bad shape. Crapped out again and the board under the relay didn't survive the second attempted relay transplant.

    Here's what I tried

    I followed all the traces back to their pins, then soldered jumper wires from the pins to the relay terminals. The relay coil is between 22 and 24, and the contacts are between 21 and 23. The black wire you see far right is the normally closed relay contact, and is connected to nothing.

    It works perfectly when I bench test it. Put 12V between 22 and 24, and the relay closes the circuit between 21 and 23. BUT my a/c still doesn't work! When I test it while it's installed in the car, pin 22 stays at 12V and never changes. Shouldn't it be switching on and off? Can I rule out the relay as the cause?
  6. jayandgee

    jayandgee New Member

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    I ran a switched and fuse-protected loop between the low cooling fan hot wire and the a/c clutch. It was a little of a shot in the dark because I wasn't sure if the cooling fan stayed on while driving down the road with the a/c on (it does). This provides a little protection in that the a/c won't come on unless the cooling fan is on, and it comes on when the a/c is turned on. It also allows the a/c to cycle on and off because the pcm also cycles the cooling fan on and off with the a/c system.

    I also needed to change the accumulator, which was rusty and leaking.

    When I can find the correct ccrm for my car at a salvage yard I'll probably change it out. The way I have it now feels a little rigged up. :wink: But.... I have a/c!
  7. jayandgee

    jayandgee New Member

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    ISU, I wonder if your system is too low on refrigerant. When you switch the a/c on, does the cooling fan kick on and the idle jump a little? From the way it sounds, your setup looks to me like it should work. There is a diode between pins 23 and 16 (between the positive and negative leads for the a/c clutch coil) that you may be bypassing with an external relay. From looking at the diagram, I'm a little confused as to why a diode is needed there, but I assume it's necessary. (FWIW, pins 16 and 5 have a diode going in the same direction as well.. Which is a diode between the ground pin for the a/c clutch and the positive lead for the fuel pump.... Weird!)
  8. white-lightning

    white-lightning FEOA Member

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    What's the last two letters on your ccrm. I have one out of a 97 escort with "AA" as the last two letters. If yours is "AA" as well then it will probably work.
  9. zx2tech

    zx2tech New Member

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    Jayandgee, and others--diodes are there to prevent flyback voltage. Without them, relays can latch (stay engaged w/o command.) I'm too tired to explain, just research it....:)

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