A/C keeps blowing my blower fuse

Wrecked944 · 07-23-2004, 12:19 PM

Okay, this one is very odd. I have a 1989 964. And about half the times I turn on my A/C, it instantly blows the fuse (i.e. fuse #1) for my blower motor. Half the time it works just fine. Very odd. And I'm running out of spare fuses !!

I can crank up the blower myself using the fan speed switch and it never blows. But when I hit the A/C button, look out !! So is there a way to disconnect the blower from the A/C? I can handle controlling the speed myself using the regular speed switch. I don't need the A/C to do it for me - especially if it blows the fuse.

And is this a common 964 problem? Any obvious areas to look at to diagnose the underling problem?

jdowty3 · jdowty3's Garage

Sounds like the fuse is blowing when the compressor clutch is trying to engage. Have you tried disconnecting the compressor wire?

ruf-porsche · ruf-porsche's Garage

Is the fuse the correct size?
You may have too small a fuse.
Don't own a 964 but you should also check to see if the a/c should be on that circuit or another circuit. Someone might had connected the a/c to that circuit.

Wrecked944 · 07-23-2004, 01:08 PM

Oddly enough, when I first blew the fuse I found a 30amp fuse in there. The spec is for 25 amps. So I am suspecting a PO may have tried to DIY the problem with a bigger fuse.

Compressor clutch? Hmmm...yes, that might well explain the sporadic nature of the problem.

Edit: I browsed Rennlist and found another 964 owner describing the exact same problem but he didn't receive any replies to his question. Interesting...

jdowty3 · jdowty3's Garage

Check out Lee Rice's article in the Tech section called "Electrical System Upgrades". The fuse the AC system is on is stressed even if the blower or compressor isn't having a problem.

ruf-porsche · ruf-porsche's Garage

From the Technical Articles By Roger Eaton

"A word about Fuses, circuit breakers and relays!!

For several years, the factory made the same mistake on every car with a/c. When they wired the fuse board on the '76 to about '79, they wired the Evaporator. circuit together with the Front Condenser. Fan circuit. So that all the elec. load was through ONE fuse. Well since those ceramic fuses can hardly handle 20 amps. the load of 30 or 35 amps. was way too much for them. The connectors turn blue, get loose and will actually melt. Check your car and if the second fuse from the back of the fuse board is distorted see if the red/white wire is connected with the red/yellow wire. If it is, separate them and connect one of them to the next fuse which should be empty. A very good substitute for these fuses or any fuse that seems to be overloaded (that is , gets hot ) is a circuit breaker. A c.b. can be wired with a tighter connection, won't blow at the slightest provocation, and will reset itself automatically.

Most all of these a/c's will have a Relay somewhere in the circuit mainly to protect the delicate switches from the high loads of the motors. Most over looked is the Factory relay located in the heater box next to the Evaporator.