Heater and servos gone awry
12-21-2017, 11:50 AM
#1
Burning Brakes
Thread Starter
Heater and servos gone awry
Apologies in advance if this answer is elsewhere, as I've been trying to find one without posting. 
When the temperature is taken off of minimum, the condenser fan pulsates, and the mixing chamber servos open/close along with that pulsating. This will happen regardless whether the compressor is engaged or not, same for whether or not on defrost.
I have a 993 CCU (I believe it's 993-659-045-01) in my 9/90-build '91. Per Tore (https://www.bergvillfx.com/porschehvac1), 6 wires need to be changed when using a 993 CCU in a 964. I did check for an existing jumper between G1 and G19, and G19 already has a yellow/back wire going into the harness and not to G1. A/C has worked previously, condenser fan resistor changed last year, and I'm in the process of changing the evaporator fans now (will write a how-to on this if my method works
).
Could this be a temperature sensor/resistor or relay for the rear fan? Or perhaps just my CCU is borked? I pulled codes with Durametric and received:
•15 - Rear blower temp sensor
•22 - Defroster flap motor (is out of the car)
•23 - Footwell flap motor
•24 - Fresh air flap motor
•31 - Left mixing flap motor
•32 - Right mixing flap motor
•34 - Right heater blower motor
•16 - Unknown DTC: 16
•43 - Rear blower motor - Stage 1
•44 - Rear blower motor - Stage 2
•45 - Inside sensor motor
I cleared the codes, and it returned with 22 and 16. No change in operation.
I'm sure this is something stupid simple that I'm overlooking. It's not crucial to solve since it's not being driven right now, but it's one of those things that is going to get my goat until it's corrected.
Will check the rear compartment blower this afternoon. Thanks in advance, guys.
When the temperature is taken off of minimum, the condenser fan pulsates, and the mixing chamber servos open/close along with that pulsating. This will happen regardless whether the compressor is engaged or not, same for whether or not on defrost.
I have a 993 CCU (I believe it's 993-659-045-01) in my 9/90-build '91. Per Tore (https://www.bergvillfx.com/porschehvac1), 6 wires need to be changed when using a 993 CCU in a 964. I did check for an existing jumper between G1 and G19, and G19 already has a yellow/back wire going into the harness and not to G1. A/C has worked previously, condenser fan resistor changed last year, and I'm in the process of changing the evaporator fans now (will write a how-to on this if my method works
).Could this be a temperature sensor/resistor or relay for the rear fan? Or perhaps just my CCU is borked? I pulled codes with Durametric and received:
•15 - Rear blower temp sensor
•22 - Defroster flap motor (is out of the car)
•23 - Footwell flap motor
•24 - Fresh air flap motor
•31 - Left mixing flap motor
•32 - Right mixing flap motor
•34 - Right heater blower motor
•16 - Unknown DTC: 16
•43 - Rear blower motor - Stage 1
•44 - Rear blower motor - Stage 2
•45 - Inside sensor motor
I cleared the codes, and it returned with 22 and 16. No change in operation.
I'm sure this is something stupid simple that I'm overlooking. It's not crucial to solve since it's not being driven right now, but it's one of those things that is going to get my goat until it's corrected.
Will check the rear compartment blower this afternoon. Thanks in advance, guys.
12-21-2017, 12:15 PM
#2
IHI KING!
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Have you checked the heater fan in the engine compartment? When mine failed, the defrost function would cycle the fans on and off. Once I swapped the heater blower motor, all CCU functions returned to normal.
12-22-2017, 12:42 AM
#3
Burning Brakes
Thread Starter
Also discovered the left mixing chamber servo is going out. I’ll jumper the relay for the rear blower tomorrow (thanks to the other posters bringing that up). Hopefully that’ll complete the diagnostics.
12-22-2017, 04:08 AM
#4
Rennlist Member
Using a 993 CCU in a 964 needs several wire changes, and there is risk of damage to the CCU if this is not done properly. The official Porsche Technical Bulletin on this topic is in fact incomplete, and the wiring changes depends on both CCU and car wiring scheme.
Your condenser is pulsating since the CCU you have is using the 964 Condenser Fan High speed output for controlling the Rear Air Selector valve. This valve is not present in a 964.
Deleting fault codes will not affect CCU operation, it is normal to gather a lot of faults over years of operation, especially on the servos due to past hiccups. CCU fault code 16 is the Outside temperature sensor. Your car does not have this, and the CCU therefore detects a fault in this circuit.
Cheers,
Tore
Your condenser is pulsating since the CCU you have is using the 964 Condenser Fan High speed output for controlling the Rear Air Selector valve. This valve is not present in a 964.
Deleting fault codes will not affect CCU operation, it is normal to gather a lot of faults over years of operation, especially on the servos due to past hiccups. CCU fault code 16 is the Outside temperature sensor. Your car does not have this, and the CCU therefore detects a fault in this circuit.
Cheers,
Tore
