Keeping things cool Oil Cooler & AC Condenser Fan

In hot weather do you hear your oil cooler or AC condenser coil fans running at the front of your car? If not you may want to look into if the fans or their low-speed fan resistors are still functioning. Most folks don't notice if their cooler fans run as they only run in hot conditions and then only very intermittently. That means for most folks, including me, there is no outward sign that they have failed. There is a concern about failed fan motors or faulty resistors raising engine temperatures or adversely influencing the function and durability of the airconditioning condenser coils. The resistors are a know failure item on a 993 and the fans and resistors are easily tested. Tore from bergvillfx.com suggests when the low-speed resistors fail the CCU controlling them default to the high-speed setting where the only symptom is a louder blower sound when running.

I have read several accounts of the original resistors used in the low-speed circuit for the Oil Cooler and the AC Condenser failing on a 993. The resistors are encased in a ceramic donut and are located in the front quarter panels, one on each side of the car. They can be tested by pulling the two relays that control the individual fans in the fuse box and jumping the two low-speed pin sockets for each relay's socket that control each fan.

The sockets to jumper are labeled on both relays, they are spade socket 30C to spade socket 87C, they are located directly across from each other in each relay socket.  (see the below wiring diagram) or their Ohm resistance value can be directly checked at their pigtail connections that for the one in the left-hand quarter panel can be accessed through the headlamp openings by removing the headlight pod. On the right-hand side, disassembly will be required to test the resistor at the pigtail end. Also if while you have the relay out you would like to test the fan motor through the high-speed setting,  jumper spade socket 30 to spade socket 87.

The jumper can be easily made by taking a short length 14 or 12 gauge solid core primary wire, for example from a piece of ordinary Romex wire, striping the end insulation and then hammering the wire flat on the ends to form a spade that fits easily into the relay spade sockets.

Using an Ohm meter on their pigtail connections they should read at about 0.45 Ohms, most meters are not very accurate as they approach zero ohms so any reading at or below an ohm is probably good to go. Also, if the resistance checks out between the wires check the Ohm value from a good body ground to one of the wires it should be an open connection (Infinite Ohms) to verify the resistor's case has not failed and the coils within have not partially or completely shorted to ground.

Tore from www.bergvillfx.com suggests that when the low-speed resistor fails the system defaults to using the high-speed setting.

The resistor on the left side can be accessed behind the wheel well liner on left-hand drive cars, the resistor on the right can only be replaced by removing the bumper cover or the cooler components behind it in the wheel well first, a big job! When they fail some folks abandon the old resistors in place relocating their replacement in the wheel well.

Here are some options to replace the resistors:

• Do nothing if you hear the blowers running at high speed and it doesn't annoy you.
• Buy the replacement resistors at the dealer and replace them through the wheel wells. The trick to moving the oil cooler to access its resistor is to remove the headlamp pod and a fastener behind it in addition to the fasteners in the wheel well that hold it. The OE resistors is kind of pricy, installing new ones involves disturbing 25 Plus-year-old Oil & Refrigerant hoses whose durability may be in question.
• Relocate replacement OE resistors and abandon the original ones in place. Relocating them behind the wheel well liners avoiding major body or component disassembly and disturbing hoses & fitting on a 25+year-old car to replace the originals.
• Update each of the  $75 original 0.45 Ohm 55 Watt resistors with a pair of 100W industrial resistors of a robust design providing between 0.4 ~ 0.5 Ohm total resistance from eBay for a few dollars. Using two 0.8 Ohm 100W resistors ganged together in parallel is a lot lower cost than finding a single 0.4 Ohm resistor rated at 200W it also allows for more flexibility in where the new resistors are mounted.
• A combination of the above option and relocating the resistors behind the headlight pods; here is a DIY project to replace and update the resistors

• Buy a 12 Volt solid-state variable speed fan controller on eBay to eliminate the resistors entirely while retaining the two-speed fan feature. I have not done this but others have reported it works quite well. In this case, relocating the controller to the inside the frunk is probably a good idea.
• Jumper the resistor's pigtail plug or the relay in the fuse box where the system becomes a one-speed controller that turns the fan on its high speed whenever the system triggers the low or high heat threshold. I have not tested this option and it is unclear if it will damage the CCU or has the potential to throw an OBD code. If Tore is correct and the system defaults to high speed when a resistor is bad anyway and so it may simply be unnecessary. The wiring diagram seems to have a feedback wire in the system whose function is unclear to me so I assume it is part of the CCU system related to On-Board Diagnostic Code (OBDC) reporting.

Here is the wiring diagram for the fan control circuit for those who entertain replacing the resistors or jumpering their connections:

The oil cooler fan is turned on by the CCU when its temperature sensor sees 75 Degrees C or more and turns off when it sees 70 Degrees C or less. If you find the fan runs for extended periods once the key is out of the ignition here are the most common causes:

• A faulty or disconnected temperature sensor will cause the CCU to default to the high fan speed.
• A failed fan low-speed resistor in this case the CCU will default to the high fan speed.
• A worn-out/faulty fan relay may stick in which case the fan remains on running the battery down.