A/C switch is HOT!

banjomike · banjomike's Garage

SO as part of my AC removal project, and baby seat installation project, I pulled the underdash AC vent out over the weekend. I have decided to keep the fan in the smuggler box since w/out the vent it blows cool air like a hurricane. So when I removed the vents, I pulled the switch out with the intent of mounting it somewhere. In the mean time I turned it on while driving in the heat yesterday, and was very lucky to discover (before it burned my carpet) that the switch was REALLY HOT. Now I understand what that asbestos looking material was around the switch housing.

Several other people have mentioned removing the AC but keeping the fan. Has anyone every tried to replace this switch? I would guess that full power for the fan is running through it. I guess a relay and a nice low amperage switch in the dash is the safe way to go.

Any thoughts?

david914 · 08-26-2003, 03:01 PM

Ya, I don't know about the older style systems, but I've been doing some work on my SC lately. I can tell you that while I had it on the bench, the fan motor on my car pulled as much as 15 amps at full tilt!

It's no wonder that the switch (and the main fuse in the trunk) get hot. If you're only going to use it on full speed, then by all means install a relay. If you're planning on using all three speeds, you'll need three relays if you want to relieve the switch of all of the load.

ruf-porsche · ruf-porsche's Garage

The evaporator fan motor is already on a relay. The problem is that the condensor fan motor may also be on the same circuit.

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.

autobonrun · autobonrun's Garage

Heat is usually generated due to resistance. A loose connection, a corroded terminal, or a corroded wire inserted in the terminal will generate heat. Grind off any corrosion, then make sure the terminal connector is tight.

david914 · 08-26-2003, 05:47 PM

Actually, on an SC anyway, the evaporator fan IS on a relay, but it's not there to relieve the load on the switch. It's there to shut off the A/C while you're starting the car. The only other relay in the A/C system is for the front condensor fan. Oddly enough, the supply voltage for EVERYTHING as Ruf pointed out, goes through ONE poor 25 amp fuse (#20). I've separated the condensor fan from the rest of the A/C and gave it it's own fuse as has been suggested, but the condensor fan itself doesn't really draw that much current (~2-3 amps) so it helps, but not much. Ruf's suggestion to use a circuit breaker makes sense. There is just too much current flowing through that one little fuse to last for any length of time. I'm on my second A/C fuse block (the one with 3 fuses toward the rear of the trunk) in 8 years. Not too bad, but it should last MUCH longer than that.