Power at the A/C Compressor

wnsgc · 09-02-2007, 04:25 PM

Greetings,

I've been working on the non-functioning a/c unit on my 85 Carrera. Last year, the previous owner converted the system from R12 to R134. Whereas I don't know for sure that it ever worked, he spent quite a bit of money on the conversion and drove it all last summer, so I'll have to assume it was working at one point, but the key word here is "assume..". Anyway, when I turn on the a/c, the a/c blower works, but the compressor doesn't turn on. I measured the power going into the a/c unit and its around 10amps.

Is this the correct amount of power going to the a/c compressor? The fuse and the relay are working fine. I am a bit confused about the relays though, as there's a relay in the front trunk, the circular type found above the fuses, but according to the parts diagrams from our host, there's another relay (part # 911-615-103-01-M206), which has a built in fuse, but I can't seem to find this relay. Any thoughts on where this may be found?

Thanks,
Scott

scottb · 04:36 PM

I'm a little unclear on what you're saying. Is there power to the compressor...right at the connection? If not, and if when it was converted to R134a they installed a high/low pressure switch, it's possible the system is in need of recharging which would cause the compressor to not kick on.

wnsgc · 09-02-2007, 04:39 PM

Sorry about not being clear. I assumed there was no power to the compressor, but when I unplugged the cable leading to the compressor, and connected the meter to the cable, it was first showing 6amps, then the more I turned the a/c on, then off, then on, etc. the amps climbed, but maxed out at 10amps. As for the high/low pressure switch, I could not find one.

wnsgc · 09-02-2007, 04:54 PM

Here's a picture. There are a number of wires going to the compressor.

Scott R · Scott R's Garage

If you have power at that connection point it's time to test the clutch. I'm a 911 owner these days, however all of my previous 944's had denso's and the clutch failed on both of them. You can check the clutch by giving it 12v from the fuse panel in the engine compartment, if it works it's going to "click" when energized. It's just a big electro-magnet after all.

2ndTARGA · 09-02-2007, 08:57 PM

Do what Scott said - jumper a known +12V source to the clutch wire and if it clicks on, then you need to trace things back to the switch to see where the disconnect is. If there is an unknown pressure cut off switch somewhere you can always buy a cheap can of R-134 and introduce it into the suction side of the compressor while running. If the clutch comes on then your wiring is OK and you have a leak somewhere in the system.

NAPA autoparts has a cheap UV test lamp you can use with leak detecting dye to find the leak.

When you mentioned testing the connection with your meter, I assume you were measuring Volts, not AMPs, as you really can't measure amps with the circuit disconnected. If you were only getting 6 volts at the compressor connector and if it the raised to 10 volts later, then you may have a wiring problem.

Ron

Hugh R · 09:04 PM

Both Scotts are correct. Run a heavy wire from the fused side of the fuse box directly to the magnetic clutch and see if it energizes it should click. Make sure you know which side of the fuse your connecting to, otherwise you could melt some unprotected wires. If your uncertain, get an inline fuse and run it from the battery with the heavy wire. And with the engine running, the center of the clutch and the outside of it should lock and spin as one. I don't know about starting at 6 amps and as you turn up the A/C it going to ten. It should be on or off. It doesn't increase voltage to grab the clutch harder as you up the A/C or anything like that. If you have a hi/low pressure switch with the conversion, you can jump it to fool the system into locking the mag. clutch. If your low on r-134a, it won't engage the clutch.

Wayne 962 · Wayne 962's Garage

I think you want to measure the voltage at the clutch to see if it's turning on or off or not. You should be able to power it too, and then it will turn on and engage the compressor on its own...

Hope that makes sense...

-Wayne

wnsgc · 09-04-2007, 03:09 PM

A couple of more points, when the engine was running and the AC switch was on for a few minutes, the voltage on the line coming from the fuse panel was 6 Volts to ground. Subsequently as I turned the switch on and off, it climbed up to 11 Volts to ground. Maybe the leads were dirty or it had a poor grounding spot. I agree, the most logical step will be to supply 12 volts directly to the clutch. If it doesn't click then I'll replace the clutch. If it clicks then I'll further troubleshoot the electrical system.
The other puzzle is what was that white thing? The 12 Volt supply wire splits in two. One Wire goes directly to the clutch (black), the other wire goes to this white thing (light blue wire). Does anyone know what that white thing is, it's located under the red high port?