993 AC Trouble and Heater Blower Motor Trouble

Jim Smolka · 08-04-2006, 07:52 PM

On the '95 993 cab, the heater and AC system is not working. With the car running, AC clutch does not pull in and the interior evap motor does not run. The same is true with the heating system. The engine blower motor and the interior blower motor run if the relays are removed and a jumper wire is connected btwn pin 30 and pin 87. Fuses have been checked. There are post regarding the replacement of the balast resistor and that will be checked in the morning.

Any ideas???

FWIW, I have an AC / heater control module from a 1990 964 C4 to use as a test if it will work

TIA

Jim

Don Plumley · Don Plumley's Garage

Probably not much help, but when I first disconnected my blower motor from the engine, the HVAC would not work. When I put in a resistor to simulate the fan, one to simulate the temp sensor, and then plugged the bypass resistor in (big rectangular thing with an open coil of wire) the HVAC worked again.

So you might want to make sure the bypass resistor (or whatever it is called) is working. There are contacts the switch over if the motor fails to protect the circuit. I bet if the system can't send power through either the motor or the bypass resistor, nothing works.

Did you look at Adrian's website?
http://www.porsche964.co.uk/technical.htm

ruf-porsche · ruf-porsche's Garage

Check any fuse or relay?

Jim Smolka · 08-05-2006, 05:32 AM

Checked fuses and bench checked relays. All were OK (MSEE)

Jim Smolka · 08-05-2006, 08:05 AM

Update.

The rear engine blower motor system was tested. On it's relay, there are 2 sets of coils and contacts. One set pins 30 and 87 the power goes directly to the blower motor. The other set, pins 30C and 87 C the power goes through ballast resistor. The motor would not turned if the contacts were jumpered. A loose connection on the ballast resistor was discovered and fixed. Now the motor runs with the either set jumpered.

Jim Smolka · 08-16-2006, 02:35 PM

Update II.

Ok aftermuch fun, the resistors for the AC Condensor and the Oil Cooler were bad. They are about $50+ each. According to the writing on the side they are rated for 0.45 ohms each. Now one can buy the OEM stuff or go to FLAPS and purchase a balast resistor mfr by Wells part # AL795 that is rated for 0.50 Ohms for $3 each. I opted for the el-cheapo route. Then cut off the wires from the old resistor and connect them to the new resistors as seen below:

When removing the resistor from the oil cooler, no need to loosen the cooler. Simply remove the lower bumper cover on passenger side, use a long extension and 10 mm sockets to loosen the nut that holds the resistor in place. Then push up on the bolt. Then reach in and pull the resistor out.

Mounting the new resistors was easy as seen in the picture below for the AC:

Jim Smolka · 08-16-2006, 02:37 PM

And for the Oil Cooler

Jim Smolka · 08-16-2006, 02:42 PM

Ok, the cooling fans were all working by jumpering the relays in both high and low speed. Still nothing. Since the final blowers were not working, they were tested also by removing the wire connector to the solid-state relay located in the top center of the trunk behind the gas tank. Applying 12 VDC to the each motor and they both ran.

The only thing left was the HVAC control module in the Dash. Now those are not cheap. Luckily, I had one left over from the 964 C4 I parted out. Plugged in the spare and the HVAC system now works.

Hope this helps for others going down a similar path.