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Unread 08-31-2009, 09:16 PM   #1
helmet993
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Default A/C Condenser Fan / Oil Cooler Fan / Evaporator Temperature Sensor

TIA for looking and reading below.

All testing was with ignition off.

I tested my oil cooler fan and A/C condenser fan for proper operation.

Oil cooler: Low/High speed on Oil cooler both good

A/C Evaporator Fan: Low speed nothing, high speed good

I used the same relay for both (popped off the relay cover and actuated both coils inside relay, then switched from R04 to R14 location). Both relays were checked for any previous owner internal jumper modifications to run high speed only.

I measured the resistance on pins 5 and 7, got 0.8 ohm for the oil cooler side and 700 ohm for the a/c side...so a/c side ballast resistor is seemingly toast, confirming my test using the relay.


My A/C blows quite cold, but if I run it for extended periods with temperature control set to the blue dot my evaporator ices up. I think the evaporator ices up because vent temperatures are quite cold, then after 30 minutes or so and after a few stops whilst running errands, I get ambient temp out of the vents and after parking the car in the garage or parking lot I get an unusually high flow of water (evaporator thawing IMO) from the drain hose under car.

If I run the temperature control knob at the 18C (9am) position it works well and the evaporator doesn't freeze up from my testing.

Here's the kicker: I have felt the a/c evaporator fan running and I can hear it, but must be running on high. During driving the fan can be heard clicking on and off every so often also.

Question 1: Will high speed operation of the condenser fan cause the evaporator to ice up?

Question 2: I looked at relocating the evaporator temperature sensor, but it doesn't really look like it can be relocated, due to the 'cover' that the sensor is fed through predicates it's location, would someone please explain how to relocate it?

Question 3: If low speed is INOP on the a/c condenser fan, is High speed substituted? Seems my high speed fan runs when a/c is on.

Last question, but related to the oil cooler fan: If I wire a manual switch behind the CCU, does anyone have a picture of what the connector and pin look like? If I wire a manual fan, no way am I going to cut the CCU harness but instead I would prefer to release the female pin of G12 (green/black wire) from the ccu harness connector and wire in the switch, therefore not making any permanent modifications to the under dash harness. Maybe I will start a new thread for this one.

Thanks,

Brett H, in South Orange County...
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Unread 09-10-2009, 02:50 PM   #2
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So I added a 2500ohm resistor in parallel to my NTC thermistor at the oil cooler.

Fan should turn on on low speed about 203F or so now instead of 230F. I only tested with a heat gun and while measuring the resistance...I am getting about 1.0kohm with temp at 230F (instead of 1.0 kOhm at 209F)...therefore tricking the CCU into turning the fan on earlier.
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Unread 11-14-2009, 07:56 AM   #3
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I think at some point you are confusing the A/C evaporator & condenser. The condenser is front left of the car with a fan; the evaporator lives under the front hood just in front of the scuttle. Not too sure it has a fan though.

Both my condenser & oil cooler fans were working on high speed but both ballast resisters were shot. There is a posting on Rennlist detailing how to make your own resisters. How I did mine is detailed here: http://www.911uk.com/viewtopic.php?t...sister&start=0
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Unread 11-14-2009, 01:56 PM   #4
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Quote:
Originally Posted by mday View Post
I think at some point you are confusing the A/C evaporator & condenser. The condenser is front left of the car with a fan; the evaporator lives under the front hood just in front of the scuttle. Not too sure it has a fan though.
The thread has a lot going on...oil cooler fan, condenser fan and evaporator temp sensor...three different systems Obviously not of much interest either!

The evap temp sensor relocation prevents evaporator icing, correct...no fan on that. An old Porsche field fix was to relocate lower to encourage compressor cycling and prevent icing of the evaporator.

I did call the condeser fan the evaporator fan in my original message...thus the confusion. I knew what I wanted to say but didn't!
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Unread 11-14-2009, 08:15 PM   #5
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I know there's a thread/DIY about the evaporator icing up too much and reasons for it over on RL, but of course, it's all iced up over there sooo ..... just sayin'
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Unread 11-15-2009, 07:52 AM   #6
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Question 1: Will high speed operation of the condenser fan cause the evaporator to ice up? I wouldn't have thought so but see below.

Question 2: I looked at relocating the evaporator temperature sensor, but it doesn't really look like it can be relocated, due to the 'cover' that the sensor is fed through predicates it's location, would someone please explain how to relocate it? Maybe cut & extend the wiring?

Question 3: If low speed is INOP on the a/c condenser fan, is High speed substituted? Seems my high speed fan runs when a/c is on.
Definite no on this, & this was why I posted details about the ballast resistors. Your ballast resistor on the A/C fan is not working preventing slow running of the fan. I would suggest you fix this 1st. From my investigations it appears the low speed fan is on 90% of the time the A/C is working; certainly whilst the car is stationery & I suspect whilst the car is moving. Higher road speed equals higher air speed through condenser & logically the fan should turn off. If you run the system on the blue dot, at high ambient temps & with the car stationery, the high speed fan should come on pretty quickly. The evaporator may ice up in these conditions.

Hope this helps.
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