martin944

On my 87 44S, the AC button switch won't come on. could it be the relay? if so do you just pull the relay off the fuse box?

Thanks!

944-LT1

I guess the first question is; when you push the switch, does it stay down and the light turn on? Does the compressor click on as well as does the fresh air blower blow air out the vents? What does/doesnt happen? Does any of the other buttons or ***** on the control panel work or is it just the AC button? it could very well be just the switch there.

First you should check the grounds. Then the fuse at 29. Then the relay at the fuse block and yeah you just pull up on it. Its alittle tough to get out as opposed to the others on the main part of the fuse block. Once out its pretty straight forward. Youre should check the relay itself for faults but its a normally closed relay which means you would need to take the plastic covering off the relay and slide a piece of paper in between the contact points to check the coil of the relay. Theres many articles online on how to test a Bosch relay through its pins which is very similar to the AC relay in your car. But to make it easy, just check for power to the relay first. Pin 86 should be the 12V+ as well as pin 30 so you should check for 12V+ in the carrier that the pin corresponds to. You should have earth at pin 85. You should have 12V+ power out of the relay to the field at pins 87a and 87. If you go at it with the ohm meter, you should have ohms between 85 and 86 (the coil). Since its normally closed youll have ohms at pins 30-87a-31. If you get the contacts apart you should have ohms between 87a and 31. Pin 30 would be nothing until the contacts close again. However there are diodes at pins 31 and 85.

Ill keep going just incase you find that the relay works.

If the switch lights up and seems functional but youre not getting air, you want to check for power at fuse 14 as well as the fuse itself. Should be a 30A fuse. If thats OK, you should check for power at the limit switch in and out. Check ohms at the limit switch which I believe is normaly open. If the system is low on refrigerant, the limit switch will stop the whole system. This is because the red/black wire at the limit switch is power from the AC relay and then to the compressor which inturn passes along a red/green wire to the DME and then to earth. There should be a heavier black wire from the limit switch to the compressor. Check this wire for cracks or shorts, etc. It is possible to check the pins at the control unit in the cabin. If you take the ***** off and the trim, it should be held in by 4 screws. Pulling it out will reveal the pins in the rear. If you get to this point (after the previous failed) youll need a schematic and not one like a Haynes manual. It doesnt go into detail far enough.

Anyway, this should keep you busy for alittle while.

martin944

thanks man, yeah, the button stays down down but the switch light stays off and the compressor does not come on. I'll check the fuses you mentioned.

martin944

I checked fuse 29 (7.5 A)and it was blown. replaced the fuse and it blows again. Any ideas?

whb944s

i have an 87 944s as well and when i did a ac charge the fuse would blow, but only when driving. I could idle and it would be fine but within minutes of pulling down the driveway it blows.

944-LT1

Not really. Is the compressor turning on when you replace the fuse....better yet, when does it blow? When you turn the system on or just after you replace the fuse?

ahh. Let me check the schematic again. Ill be back.

martin944

With a new fuse the compressor clicks on, and blows cold air. after drving a bit it blows.

944-LT1

So, we have ruled out the switch in the cabin and the relay. After looking at the schematic, it would seem as though the compressor clutch may be drawing too many amps to stay engaged. A way to test this is to run a straight wire from the compressor (should be a larger gauge black wire) with an inline fuse (7.5 amp) to the battery with the car running. If the inline fuse of your makeshift power supply blows, its the clutch engaging and you will need a new clutch if available or simply a compressor. It also could be the diodes that prevent voltage spike either in the relay or clutch back to the DME (save that for last). Another way is to check the amperage off the compressor power feed (see pic) and compare it to spec's.



The best way is to (with the battery disconnected) go ahead and take the wires OFF the compressor. Replace the fuse and run the engine just as before. If the fuse does not blow...theres a lead! You can use your headlight bulb as well to check the wiring of the circuit if the clutch is ruled out. With two alligator clips to the clutch connector and to the headlamp. If the fuse blows, theres a wiring problem. Which could be simply a wire thats rubbing where it shouldnt.

I would also look towards the radiator fan amperage at high or AC speed. It may be drawing to many amps and causing the blow. Although i cannot trace the compressor circuit directly to the fans as it gets wacky in the control "brains." So this may not be it.

If anything, DO NOT install a larger fuse. You could cause damage to the circuit and its dependents or worse.....FIRE! I know these 7.5ers are difficult to find readily but dont do it. Use a 5amper if youre out.

Try these things and good luck!