2005 Vectra low voltage at the A/C compressor, shop can't find the problem

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oldryder

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Avon MN
Truck repair facility giving up after 5 hours of diagnostics at $128/hour.

They report the wire supplying voltage to the compressor is only providing 8-9 volts which won't engage the clutch. The clutch will engage if 12v. is "hot wired" to the clutch.

one solution is to add a 6v. relay; use the 8-9v. signal to pull in a relay that switches 12v. direct from the nearby battery.

does anyone know what the correct amp draw for the compressor clutch is? it's possible the clutch solenoid is failing such that it'll still work with a supply that can provide more current (the hot wire) than the coaches internal wiring.

other comments are welcome. I'm reluctant to go to another service shop after already spending over $600 essentially for nothing.

mark in MN
 
I'd find another shop. 5 hours of "troubleshooting" is more than enough time for a mechanic to replace everything in the circuit. When they jumpered the clutch to the battery, a DC clamp-on current meter would confirm the clutch isn't drawing an excessive amount of current (mine cost $45 on Amazon). If the clutch current is OK, the next step is to systematically trace the voltage at each point between the battery and the compressor clutch and see where it's going away (it has to disappear somewhere).

Adding a relay is a band-aid that only masks the original problem and will work until whatever is bad gets worse. This is also another example of that shop's lack of electrical knowledge. Voltage drop is directly related to how much current flows through the circuit and a relay draws a lot less current than the compressor clutch so it will produce less voltage drop. It's likely the voltage will return to close to, if not the full 12 volts. That's too much for a 6 volt relay.
 
Lou, good point on the relay voltage. I am working my way thru the prints now. doesn't seem like it should be that difficult of a problem but the service writer mentioned the tech had no prints. That pretty much explains how he wasted so much time.

"Adding a relay is a band-aid that only masks the original problem and will work until whatever is bad gets worse." - Agree. what I really need is to determine if the clutch solenoid is drawing the correct amount of current. I do have a DC ammeter but I need to know the correct amp draw.
 
I agree with Lou on every point, find another shop. You can survive a bit without AC.

I would also try to negotiate the cost of their (lack of) diagnosis. Point out that you were expecting to pay for results, of which you received nothing. You agreed in good faith to pay for a solution, again, that you didn't receive. You will most likely will pay something but hopefully much less than the shop rate they are asking for.

Kevin
 
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Is this the air conditioning compressor or the air brake compressor?
Cummins air compressors are controlled by tank pressure. No electric involved.
At least they used to be...

Though I've had them go on the fritz and need a really good cleaning. There is a valve in the head that gets dirty and will jam open so it won't build up pressure.

Kevin
 
Gary; Problem is dash A/C. yes I printed out the 2005 Vectra prints and am trying to find the switch(s) and wiring to the compressor. No luck so far finding what I need but I think thats mostly because I'm still learning the symbol conventions. I've looked at a lot of elec prints for industrial controls in my working life so I think I will figure it out. If you happen to know the print number and page(s) where the things I'm looking for are please tell me.

thx
mark in MN
 
There's some useful diagrams out there - search for SCS Fridgette and or Victory Climate. I did some major refurbishing on our dash air a few months ago and I found some very useful info in the Interwebs, I didn't save the links though. I should have put those in our Winnebago and chassis resources sticky thread.
 
Ray-IN - thx for document links. Got the service report today and the report on A/C diagnostic effort is quite detailed. With the prints and documents I think I'll be able to figure it out.
 

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