Slipping A/C Clutch VP

[Chuff]

Howdy all,

Had the VP regased a couple of months ago and in the last week or so I have noticed that it's not working too well. I had a look under the bonnet and noticed that the internal area of the pulley which normally engages when the compressor is running is barely turning over. What the...?

Anyone know if this sort of thing is repairable?

Thanks.

[Chuff]

OK... I done a full analysis on what's going on, and it's got me stumped.

When I turn the air conditioning on via the climate control, +12 volts is sent through the pink wire into the low pressure switch on the receiver drier. Since the system is full, the switch completes the circuit and +12 volts is sent out the other end. The +12 volts can then be seen at terminals 86 & 30 at the A/C compressor relay holder in the relay box located in front of the driver's side strut tower under the bonnet. This scenario is also detailed in this post. vs a/c wiring diagram. It also mentions that the the negative side of the relay coil (pin 85) is supplied by the PCM, which I'm assuming in my VP is supplied by the BCM. Either way, pin 85 is supplying a ground as it should. And finally, pin 87 goes to the A/C compressor to engage the clutch. All the voltages I have mentioned here have been taken with the relay removed.

Now the strange bit. With the relay in place, I heard and felt the relay vibrating, so I re-checked the voltages with the relay's 4 terminals just sitting in position on the relay holder. In this position I could probe the voltages again, and pins 86 & 30 have dropped from battery voltage to 9 volts. At this stage the A/C compressor clutch does not engage. With the relay still in its raised position I applied battery voltage to terminal 86 and the A/C compressor clutch engaged.

With all this information I'm now thinking that the voltages at pins 86 & 30 deteriorated from battery voltage to 9 volts, and it was during this time that I noticed the clutch slipping. Incidentally, the A/C compressor clutch no longer engages at all at this voltage. I can't prove this theory without supplying a variable voltage to the pins, but I believe it to be a fair assumption.

And it gets even weirder. Pin 87, which is the pin that finally supplies the +12 volts to the A/C compressor clutch, has a reading of battery voltage, even though supply pins 86 & 30 are at 9 volts. I got no idea on this one.

Also, if it helps, if I remove the relay and supply a direct +12 volts to pin 87 the A/C compressor clutch engages as it should.

Hope you can wrap your head around all this stuff. If anyone has any idea whatsoever as to what the hell is going on, please let me know, as I'm not going to be able to sleep until I figure this one out.

Thanks.

Chuff.

[Chuff]

More testing...

Forgot to mention that I swapped relays with a known good one and it made no difference.

Also, In addition to supplying battery voltage to pin 86 I also supplied a ground to pin 85 while the relay was in, and this made no difference either, so the ground at pin 85 is OK.

Chuff

[Chuff]

More testing, more results...

While running battery voltage directly into the relay socket, thus engaging the A/C compressor, I discovered that the compressor was vibrating at around 1500 RPM, then nothing until around 3000-35000 RPM when it would vibrate again. The power steering pump, which looks like it's attached to a common bracket with the A/C compressor, also vibrates at the same RPM values. This vibration is there only when the A/C compressor is running. Could this have anything to do with the harmonic balancer on the engine. Does anyone know at what revolutions the natural harmonics of the GM 304 V8 occur? If it's at the same values, could it be the harmonic balancer on its way out?

Also I've been doing some further reading and now believe that there is a high pressure switch located in line between the low pressure switch & the relay socket. I thought, maybe my drop in voltage in the relay socket may be caused by a faulty high pressure switch, which would only drop its voltage when the A/C compressor was running, but probing the socket while the A/C compressor was running showed the values were what they should have been, and the act of placing the relay into the socket produced the drop in voltage, not the fact that the A/C compressor was running. I also tested the voltages going into & out of the low pressure switch and both were battery voltage indicating a good switch and sufficient pressure in the system.

Although the 2 paragraphs above discuss different problems, they are inherently related, so solving 1 problem may or may not solve both.

I'm at a real loss here and don't know what to do next. Of particular interest to me are the vibrations at 1500 & 3000-3500 RPM. As for the voltage dropping when the relay is put into place, WTF!

Thanks.

Chuff

[PRH]

Ok so what happens when ya join pins 30 - 87,sounds like ya go a crook connection,check the voltage at the fuse holder and then the relay block,if its 9 volts there then ya problem lays before that point.
Regards Phillip

[Chuff]

Ok so what happens when ya join pins 30 - 87,sounds like ya go a crook connection,check the voltage at the fuse holder and then the relay block,if its 9 volts there then ya problem lays before that point.
Regards Phillip

Damn it, the only electrical combination I didn't test, directly eliminate the relay and run the voltage straight from pin 30 to 87. It's gotta be it. Can't be anything else...

Well, just tested it and it looks like it's something else, as joining pins 30 & 87 turns the A/C compressor on and it runs sweet.

Thanks PRH, I've read quite a few of your posts while trying to track this down, and I'm glad you're on board. Auto electrics are a walk in the park for me, but this has me completely stumped!! Even once I figure out the relay problem, I still need to figure out why the A/C compressor vibrates at 1500 & 3000-3500 RPM when it's running, 'cause driving it with this vibration will definitely destroy things.

Chuff.

[PRH]

g'day again chuff
glad to hear we have acheived something,still doesnt tell us whats happenining with it though,if the voltage across the coil drops the contacts will vibrate as well,not sure as to where the relay coil gets its feed from, maybe from the climate control i could see on my ute when it cools down.
As far as the vibration that can be caused by over gassing

[Chuff]

g'day again chuff
glad to hear we have acheived something,still doesnt tell us whats happenining with it though,if the voltage across the coil drops the contacts will vibrate as well,not sure as to where the relay coil gets its feed from, maybe from the climate control i could see on my ute when it cools down.
As far as the vibration that can be caused by over gassing

Thanks PRH,

Both the supply voltage to pin 30 & the coil positive voltage to pin 86 are supplied from the same feed. I have attached part of a page which I scanned which shows exactly how it all works. Scan was taken from the Engine Management System section in volume 4 of the factory GM manual for my VP Series 2 Calais.

The circled area in the middle is what applies to me, as I have climate control. Everything as you see it in the circled area is exactly the way my car is. Your suggestion of joining 30 & 87 simply mimicked what the relay does when the coil is energised, and all worked well when done this way, however, with the relay in place, 30 & 86 dropped in voltage from battery to 9 volts, and yes, you can hear and feel the coil oscillating within the relay.

In summary, with no relay in place the voltages at 30 & 86 read battery, and 85 is supplying a good ground. Put the relay in place, and the voltages at 30 & 86 dropped to 9 volts, and I've just checked again and now it's at 5 volts, so it may be dropping or simply fluctuating, I'm not sure. Either way, the A/C compressor clutch does not engage. Supplying a hard ground to pin 85 via a grounded wire makes no difference, so it's safe to say that the ECU is supplying a good ground out of C2. Supplying a hard wired positive to pins 30, 86 or 87 and the A/C compressor comes to life.

I'm also very interested in your statement regarding vibrations being caused by over gassing. Could it be possible that the system is simply over gassed? This would explain both the vibration & the possibility that the A/C High Pressure Safety Switch, which is normally closed, is just opening enough to drop the voltage to pin 86. Might sound far fetched, but I see no reason why it could not happen. I've known stranger things to happen with cars.

Further thinking, and taking into account that the A/C was running fine for a few weeks after its regas, then I can only see 1 of 2 things have happened. Either the A/C High Pressure Safety Switch is on its way out, or the pressure has increase over time within the system? I would have thought the later not possible in a closed refrigeration system, but I'm not a fridgie so I don't know. An easy way to test this theory would be to purge a small amount of refrigerant out of the system and see if it fixes the problem. Aside from the obvious impact on the ozone layer (I'll plant a tree for all you greenies out there) is there any reason I should not purge the system? If I proceed, for how long should I purge? Half a second too long?

I'd be wrapped to my back teeth if this was to fix the problem.

Thanks again.

Chuff.

[Wrayza]

I'm also very interested in your statement regarding vibrations being caused by over gassing. Could it be possible that the system is simply over gassed? This would explain both the vibration & the possibility that the A/C High Pressure Safety Switch, which is normally closed, is just opening enough to drop the voltage to pin 86. Might sound far fetched, but I see no reason why it could not happen. I've known stranger things to happen with cars.

This sounds like something to me, I'd be inclined to remove the connector from the high pressure safety switch and test the resistance of the switch. Firstly with the compressor off, then with the compressor on using the method you found to make it engage.

If you start to get a high resistance (anything over a couple of ohms) then thats probably where your losing your 3 volts. It wouldn't take much resistance with the current an electronic clutch draws and the wiring thats usually ran to them (16-14 gauge?)

Goodluck mate, I hate these problems too.

[vsv8berlinawag]

What was the outcome as I have what appears to be a slipping clutch once the compressor is working hard on days over 35 degs ?