Air Compressor Clutch Missing 12V~
03-31-2007, 06:25 PM
#1
Rennlist Member
Thread Starter
Air Compressor Clutch Missing 12V~
OK here's a problem that has puzzled me in my late 95 993.
The Air Compressor clutch won't come on most of the time. It's not a recycling problem.
It does come on and stays on sometimes if I hit a bump on the road.
Also if I supply 12V to it it's fine. Cooling in the car is fine when the clutch is engaged.
YES, I checked the connection to the compressor on the right fender
So far I vaccumed and refilled the system with the proper amount of 134a.
I replaced the pressure switch with a new one.
I checked the fuse and relay on the left side of the engine they are both fine but it's missing the voltage to key the relay.
I checked all fuses and relays in the luggage compartment, all OK.
The only thing left for me to do now is to take apart the air control unit in the dash and check for poor solder joints.
Since the clutch sometimes engages when I hit a bump, it only indicates a bad connection somewhere.
I have all the diagrams and I'm capable of any electronic troubleshooting but this one has me a bit puzzled,
Does anyone have any other suggestions that I may have missed?
Does anyone have a spare AC/Heater Contol Unit? Thanks, Chris
The Air Compressor clutch won't come on most of the time. It's not a recycling problem.
It does come on and stays on sometimes if I hit a bump on the road.
Also if I supply 12V to it it's fine. Cooling in the car is fine when the clutch is engaged.
YES, I checked the connection to the compressor on the right fender
So far I vaccumed and refilled the system with the proper amount of 134a.
I replaced the pressure switch with a new one.
I checked the fuse and relay on the left side of the engine they are both fine but it's missing the voltage to key the relay.
I checked all fuses and relays in the luggage compartment, all OK.
The only thing left for me to do now is to take apart the air control unit in the dash and check for poor solder joints.
Since the clutch sometimes engages when I hit a bump, it only indicates a bad connection somewhere.
I have all the diagrams and I'm capable of any electronic troubleshooting but this one has me a bit puzzled,
Does anyone have any other suggestions that I may have missed?
Does anyone have a spare AC/Heater Contol Unit? Thanks, Chris
03-31-2007, 07:38 PM
#2
Rennlist Member
On many AC systems, there is an external ( ambient) thermistor to set a reference temp:if this is non functional, the controller remains confused as what to do. eg., on the 928, it is located on the cooling air hose to the alternator; however, I do not know if or where it is on the 993 ..... but it may be a point to check, as you have covered most issues already.
The AC clutch is directly interlocked with the low pressure switch .... low pressure = no 12v, but you have checked that.
The AC clutch is directly interlocked with the low pressure switch .... low pressure = no 12v, but you have checked that.
04-01-2007, 01:31 AM
#3
Rennlist Member
Thread Starter
I took the control box apart and checked all the joints on both sides under the scope, all are perfect so it's not a loose connection in the Control Unit.
I think the White/Orange wire from the clutch relay goes to a module under the drivers seat according to the OnDemand5.com schenmatic.
I need to check this out further. Chris
I think the White/Orange wire from the clutch relay goes to a module under the drivers seat according to the OnDemand5.com schenmatic.
I need to check this out further. Chris
04-01-2007, 09:33 AM
#4
Addict
Rennlist Member
Rennlist Member
The other one that tells the CCU to stop the clutch is the evaporator sensor. It isn't "inline" to the clutch like the pressure sensor is, but just a feed to the ccu. Maybe another place to look before you dig into the CCU.
