Hi All
I'm new to this forum as I only recently acquired a 1994 C2 993 (non air conditioned)
After a short while of ownership I found that the heating system (which I hadn't checked during the purchase in the summer!) was not working.
it took me a week or two to get to the bottom of the problem with many thanks to the amazing Tore (Bergvillfx.com) who guided me to the solution. So I though I would post my findings to help anyone who may encounter this same issue.
The Fault:
1. with ignition on front blower fans would run when i turn the blower through the different speed on the CCU but when I try to turn the heater temperature knob up on the CCU the front blower fans cut out.
2. press the demist button on the CCU and the front blower fans run for a second then cut out.
what did next:
1. In the engine bay I removed the resistor from the heater duct and checked if this was ok (it read 0.5 Ohms across the terminals, so all
ok there!)
2. I removed the double relay outer case for the rear blower fan and then put it back in place. I then pressed each one manually, the high speed worked easily the lower speed required me to push the contact very hard but when it did eventually make contact the rear blower fan did run. on closer inspection of the relay once removed it was blackened and burnt out with no contact points left (photo of this I'll add tonight).
3. Then I removed the temperature sensor in the rear heater tube, visually it looked damaged and when applying a meter no resistance was found! so definitley trashed.
4. I replaced the relay and temperature sensors with new ones thinking this would fix everything. How wrong I was!
Next Fault:
so now I have a new problem, when I turn on the ignition I find the rear blower fan goes into full speed, when i turn the ignition off the rear fan stops and have no controls at all on the CCU!
What I did next:
1. check the continuity between the 2 temperature sensor wires in the engine bay to the pin connector on the rear of the CCU (G10, G18) to see if they were no longer joined, these were ok so definitely no breaks in the wires.
2. so the problem looked like the CCU itself, so I removed the CCU and slowly took it apart to look at PCB's inside.
3. Close inspection of the 2 main circuit boards show a track that had blown/lifted and could be traced back to pin G18 sensor ground.
4. I soldered a bridging wire to bypass this damaged track and then checked the connection to pin G18 and hey presto all good again.
5. Cleaned up the CCU while it was apart.(good opportunity to get the dirt from behind the slide controls)
6. Reconnected the 2 large connectors to the rear of the CCU (leaving the CCU out of the slot in the dash as I was not sure if it would have to come out again).
7 Ignition on, great news all functions of the heater now work perfectly and rear blower does not come on unexpectedly.
8. took the car for a run to get it hot and checked the heater works and directs the heat to the right places, all good so put the CCU back in the dash.
I assume the combination of temperature sensor and relay failing contributed to the failure of the PCB in CCU but I'm sure Tore will have a definitive answer to this.
I am now a very happy chap as previously my Porsche specialist diagnosed the problem as the CCU but wanted £1300 +vat for a new CCU plus fitting and to be honest that was not the only problem so I question if they would have ever discovered it?
Sorry if my description of the issue and resolution is basic but I hope it can help anyone else who encounters this issue
Many thanks again to Tore for his help! :thumb: [/list]
I'm new to this forum as I only recently acquired a 1994 C2 993 (non air conditioned)
After a short while of ownership I found that the heating system (which I hadn't checked during the purchase in the summer!) was not working.
it took me a week or two to get to the bottom of the problem with many thanks to the amazing Tore (Bergvillfx.com) who guided me to the solution. So I though I would post my findings to help anyone who may encounter this same issue.
The Fault:
1. with ignition on front blower fans would run when i turn the blower through the different speed on the CCU but when I try to turn the heater temperature knob up on the CCU the front blower fans cut out.
2. press the demist button on the CCU and the front blower fans run for a second then cut out.
what did next:
1. In the engine bay I removed the resistor from the heater duct and checked if this was ok (it read 0.5 Ohms across the terminals, so all
ok there!)
2. I removed the double relay outer case for the rear blower fan and then put it back in place. I then pressed each one manually, the high speed worked easily the lower speed required me to push the contact very hard but when it did eventually make contact the rear blower fan did run. on closer inspection of the relay once removed it was blackened and burnt out with no contact points left (photo of this I'll add tonight).
3. Then I removed the temperature sensor in the rear heater tube, visually it looked damaged and when applying a meter no resistance was found! so definitley trashed.
4. I replaced the relay and temperature sensors with new ones thinking this would fix everything. How wrong I was!
Next Fault:
so now I have a new problem, when I turn on the ignition I find the rear blower fan goes into full speed, when i turn the ignition off the rear fan stops and have no controls at all on the CCU!
What I did next:
1. check the continuity between the 2 temperature sensor wires in the engine bay to the pin connector on the rear of the CCU (G10, G18) to see if they were no longer joined, these were ok so definitely no breaks in the wires.
2. so the problem looked like the CCU itself, so I removed the CCU and slowly took it apart to look at PCB's inside.
3. Close inspection of the 2 main circuit boards show a track that had blown/lifted and could be traced back to pin G18 sensor ground.
4. I soldered a bridging wire to bypass this damaged track and then checked the connection to pin G18 and hey presto all good again.
5. Cleaned up the CCU while it was apart.(good opportunity to get the dirt from behind the slide controls)
6. Reconnected the 2 large connectors to the rear of the CCU (leaving the CCU out of the slot in the dash as I was not sure if it would have to come out again).
7 Ignition on, great news all functions of the heater now work perfectly and rear blower does not come on unexpectedly.
8. took the car for a run to get it hot and checked the heater works and directs the heat to the right places, all good so put the CCU back in the dash.
I assume the combination of temperature sensor and relay failing contributed to the failure of the PCB in CCU but I'm sure Tore will have a definitive answer to this.
I am now a very happy chap as previously my Porsche specialist diagnosed the problem as the CCU but wanted £1300 +vat for a new CCU plus fitting and to be honest that was not the only problem so I question if they would have ever discovered it?
Sorry if my description of the issue and resolution is basic but I hope it can help anyone else who encounters this issue
Many thanks again to Tore for his help! :thumb: [/list]