I am new to this forum but I have found answers to all of my questions here. Until now... Hopefully someone can help me. Car is a 1994.

Problem: recently my climate control has been working intermittently. All the buttons were working, but the whole unit would just shut off and come back on randomly, like it was losing power. I did some research and decided to try taking the CCU out and cleaning all the connections. I cleaned all the pins off with an eraser then put it back together and it worked perfectly... for a day. Then it would turn off and not come on at all. The screen was backlit but buttons didn't work and it didn't display the temp like it should.

So I took it apart again and cleaned everything metal in there with electrical cleaner. I checked the circuit board and everything looks to be soldered fine. When I put it back together it still wasn't doing anything. I wiggled the wires on the harness that plugs into the back of the CCU and it turned on. The weird thing is, sometimes the blower will come on when I wiggle the wires even if I disconnect the CCU from the harness. When the CCU is getting power now, the buttons don't all work and the ones that do work don't do what they are supposed to do. I am thinking the wiring harness is bad. Any ideas? My black on black hardtop isn't as fun to drive in this heat without A/C...

 

sounds to me like possibly a bad ground for that portion of the harness. Any other work been done on the car recently that might have disturbed a ground connection?

 

Nothing recently, at least not that I know of. I just bought the car a few months ago and haven't done anything electrical on it besides a new battery when I first bought it.

I am wondering if I can replace the harness or trim the wires then reconnect them or something.

 

one possibility is the A/C heater programmer.

 

I was just reading some other threads about that. It sounds like it might be the problem. Where is it located?

 

A good possibility.

It's located under the LH side of the dash, up above where the accelerator pedal is mounted.

 

All the wiggling must have done something because now the control unit is staying on. The buttons don't do what they are supposed to do (temp down = temp up, recirculate = off, defrost = temp down, etc) but the display and back lights work. Is there a way of pin pointing whether the problem is the programmer or the control unit? I am going to take a look at the programmer tomorrow and check out / clean the connections there.

 

The control head sends two control signals to the HVAC programmer. One is the function control that tells it which HVAC doors to open/close. The other signal is used to control the blend door motor. There are no signals going from the HVAC programmer to the control head.

The HVAC programmer controls the blend door motor. There is a feedback potentiometer on the blend door motor that tells the control head the position of the blend door.

If wiggling wires causes something to happen/not happen then there are two possibilities: one is that the contacts in the connector are dirty and not making constant contact (intermittent). The other is that the wire is broken inside the insulation or there is a bad connection from the wire to the connector contact. I have seen contacts that were crimped incorrectly and broke the wire.

I have a vague recollection that one post said wiggling the wires with the connector not plugged in caused problems. That means that the insulation is bad and wires are shorting together inside the harness. You need to unwrap the harness tape and see what's happening inside.

 

Thanks for the explanation about the communication between the programmer and control head. Good stuff to know. You are right that when I wiggle the wires on the harness with the head unplugged the air would come on. I am guessing there is a short in the harness. The only tape is around the wires going behind the dash. No tape on the harness. Could you explain what you mean? Thanks!

 

Harness tape looks like regular electrical tape but it doesn't have any adhesive. No sticky mess when you unwrap it. You can unwrap it and then wrap it back up with a little electrical tape on the end to keep it in place.

 

I pulled out the programmer and checked and cleaned the connections there. Still having issues so I pulled apart the control head one last time. I guess last time I connected the two circuit boards together I made the mistake of shifting it over one pin. Kind of like when you button up your shirt with the buttons in the wrong holes... lol silly me. So I put it back together correctly. Now all the buttons are working great, but I still lose power randomly when driving around. Sometimes the unit just turns off then back on quickly, other times it will stay off for my whole drive.

Cliff, there wasn't any tape on the harness, but just by looking at it I can't see any problems. Doesn't mean there aren't any, I know. Do you think I should try finding where the grounds lead to and check that? Or just assume the harness is bad and replace it?

 

No tape on the harness? I don't understand that one. What holds the wires together in a bundle?

I'd be pulling the harness apart and looking to see what the individual wires are doing.

Is the unit actually losing power or just the display/LEDs not working? Do the buttons still work when the unit has lost power? Did you try wiggling the A/C fuse (not sure what it's called on your year, might be GAUGES). I know on my car the CTSY/CLOCK fuse supplies the backup power for the memory in the control head. The rest of the power comes from a different fuse.

I'm 99% sure the brightness of the display/LEDs is controlled through the radio. Do you have an aftermarket radio? If so, there might be a bad splice job on the wiring.

 

I will post a picture of the harness later tonight or tomorrow - I can't figure out how to get the wires out.

What I mean by losing power is, the backlight stays on, but the display goes blank, the green LEDs go off, none of the buttons do anything, and if my AC / fan was on it shuts off. I will try wiggling the fuses again and maybe spray some cleaner in there.

I have the Bose premium stereo that came with the car. It works fine. My FSM should be here next week some time.

 

Check fuse #18 (10A). It is the A/C clutch fuse but also supplies power to the control head, programmer, defogger relay. If the fuse is loose or corroded, or the wiring from it has a poor connection somewhere it will cause the problem. (So if you loose this 12 volts power, all aspects of the A/C system has no power...except the blower, its a different power feed).

If you listen carefully, you can hear the defogger relay click when you turn it on and off. It is a low sound and the engine has to be running so things need to be as quit as possible. See if you can hear the relay when the A/C is working normal. Then listen to the relay when the A/C dies. If you don’t hear the relay then, it's a power problem. If you do hear the relay, then you know the fuse is working and the problem is elsewhere.

The only other way to check power is to measure pin 1 of the connector of the control head to see if there is 12 volts there with the key ON.

When you say "The screen was backlit", was that because you turned the key ON, or because you turned the running or head lights on?

Just wondering if there were any other problems with the car.

 

Update:

I have been on vacation and had family in town, but now that things are back to normal I went ahead and ordered a wiring harness for the control head. I figure it would be better to eliminate that before I start throwing $400 at a control head or programmer. I just cut out the old one and spliced the new one in. That was a couple days ago and everything is working just fine now! (knock on wood...) Glad I finally have a working AC and am only out 25 bucks.