Eric Kasir

OK, following a meet with fellow UK Rennlisters last night, I noticed something odd about my aircon.

When you switch it on, the front oil cooler fan seems to switch on for five seconds or so / switch off for five seconds, going in a constant cycle like this. I think it is the oil cooler fan - seems to be coming from the front right hand side of the car (US passenger side).

Has anyone experienced this or have any suggestions?

Many thanks
Eric

Steve in the UK

Eric I think I may have a lead for you.

Look at the recent postings on the list under the heading:

Topic: Oil Cooler Fan Running Continuously in Slow-Speed

It was sent in by Russell Graanar?? It explains the link between the AC and the oil cooler fan. It suggests that there is something electrical at the heart of your problem.


Steve

Steve in the UK

Sorry, it was Randall and not Russell.

Regards

Eric Kasir

Thanks Steve

Randall G.

Hi Eric,

The oil cooler & A/C relays do share the same relay control power--they're shorted together. Terminal #8 is the relay control power:

Oil Cooler/AC Condenser Relays ...

So, if one is cycling on-and-off, I would think the other would, too.

The relays also get their main power from the same bus (different wires), and the relays are identical. Other than these similarities, I'm not aware of any other interconnection.

If you haven't found it already, the A/C condenser fan is in the left-front fender. It should come on when the A/C is running. The oil cooler fan is in the right-front fender. You can see both fans by laying on the ground and looking up into the open grill.

Eric Kasir

Randall, appreciate the info - I can't hear the A/C condenser fan when the A/C is on, so something strange definitely going on. I'll have a good look over the weekend.

Regards
Eric

Randall G.

Hi Eric,

Just to be clear, I should add that while the A/C condenser and oil cooler fans (or blowers) share the same relay control power, their "start command" wires from the climate control unit (CCU) are separate. So, they run independently of each other.

Both the A/C condenser and oil cooler fan relays have two (2) "start command" terminals--one for slow, one for fast-speed. All are connected to the CCU, with the exception of the A/C condenser fast-speed signal, which comes from a 3-level freon pressure switch.

The relay control power (terminal #8) is a constant source of 12V power that's "hot" with the accessory and ignition positions.

When I referred to "main" power, I meant the (high-current capacity) 12V power that is supplied to the fans, via the relay. This power is always hot, even with the ignition off.

The CCU will only send a "start signal" when the ignition is on. That's why it's okay to for the main power to always be hot. Without the start signal from the CCU, the relay will not reposition to power up the fan.

Good luck this weekend!

My Q Ship

Eric,
It is most likely your low speed fan resistor that has failed (I see this problem constantly). It is mounted on top of the oil cooler air plate. If you have a C2S,C4S or Turbo you will have to pull the bumper assy. to gain access.If yours is just the normal narrow body you'll only need to pull the R/S inner fender and lower shin spoiler portion of the bumper (the bumper part right under the cooler).
Q

micnicholas

Not to highjack but I have a similar problem, a/c fan just doesn't kick on, a/c is cool but deffinately not cold. Question is, the fan should always run when a/c is turned on, is that correct? if so, see relays I assume. thanks

Garth S

The AC fan should always run at low speed when AC is energized at the dash CCU module .... the fan switches to high, which bypasses the (low speed) resistor based upon high(er) temps/demand as seen by the thermistor.

Unlikely your relays - swap R04 and R14 if you wish to check, as the oil cooler system is identical.

As Q Ship says above, your ceramic resistor is cooked ... as is that of the OP.

Replace in kind ... or check my old posts for a bullet proof lifetime resistor DIY

ToreB

You have a very common fault. The low speed fan resistor is out of order, and the CCU must run the A/C condensor fan at high speed in intervals to keep up. This is not a good condition, there may be exsessive pressure due to this, and the resistor must be replaced as soon as possible.
You may have the same issue on the oil cooler fan, a similar resistor is used there to run the fan at low speed.
I changed both my resistors in an hour.Here's how:
http://members.rennlist.com/rgranaas...eplacement.htm
Regards,
Tore

Don't lift

Just wanted to clarify something......always learning something new here !

1) Is there only ONE resistor for both low and high speed fan for the oil cooler?
2) How about the A/C condenser fan......ONE resistor for both the low and high speed?

_____________
'97 Blk/Blk C2S

Warpig

Two resistors total. One for the oil cooler side, one for the AC condenser side

Nick

MarkD

Nick is correct, of course

to elaborate bit, there is one resistor assembly and relay both for the AC condenser fan and the oil cooler fan. One resistor per side, oil cooler on the right, AC condenser on the left.
both can be tested via a jumper wire after the relay is removed

more detail on this test is available via pcarworkshop.com

these are both very common failures

Garth S

Just to elaborate on the correct answers already received ... one ~0.5ohm resistor per side - which drops/attenuates voltage for the low speed selection: high speed is full battery voltage - no resistor ...