BSeery

My 1980 has a strange problem with the interior vent/ air conditioning fan.
It works fine in the high speed setting but will not work at all in any of the other lower speed settings.
I checked each and every fuse at the fuse panel, so it's not a fuse.

The only thing I don't know about is this plug thats coming out of the top of the a/c housing on the firewall. It's a 4 pronged plug that goes into a small wire plug that is right next to the high speed fan relay. What is that part and what does it do?

Any ideas on the lower speed fan settings and why they do not work ?

rihwoods

My 78 works in all but high speed. ????

slaine

The plug on top of the aircon bulge at the firewall, is connected to ballast resistors. Under the plug you will see an oval shaped cover held in place to the aircon bulge by two small screws. Remove the plug and the two screws and lift the cover up, attached is several long springy resistors. If the switch at your console isn't bad, the problem is probably the resistors. Make sure that your contacts are clean at the plug. I had the same problem several years ago on my '80 after checking the switch and cleaning the contacts, I replace the resistors and BINGO multi speeds again. You might want to check and see if the general ground contact to the blower motor is clean and grounded properly. I hope that this helps.
Mike

BSeery

That is usually a sign of a bad high speed relay. It's the silver rectangular electrical box on the passenger side firewall.

I know the fan and the fan ground are ok because I do have the high speed. I will go look at those resitors and clean the contacts later tonight.

Thanks for a place to start.

ffas23

Mike I have always replaced the whole thing with a new one. That part has gone bad on alot of my vehicles. Always thought about just going to Radio Shack or another electrical parts store and just buy the resistors and replace them all. Is this what you did? Resistors are cheap to buy. It should be alot cheaper in the long run. Let me know.

slaine

I always replace the whole resistor assembly. I didn't think that Radio Shack had those type of ballast resistors. Boy, if they do, it should be cheaper!
Mike 8)

BSeery

How do you tell if those are bad? I pulled the assembly out and it looked like some long metal tabs with metal coils connecting them. They were all connected to something.

Also, that 4 pronged plug that goes in to it, can I test voltages there to tell me if my switch in the car is good or bad ? What should I get voltage wise from each wire on that connector?

ffas23

I never tested them. They were cheap enough and available on most of my older cars that I would just go to the dealer and purchase another or take one out of another car to try if it was the same. I know this is no answer but it's the truth.

carl a

you need a multimeter,each one of those coils of wire is thicker/thinner than the other,causing resistance,slowing down the motor, so you would be checking with a ohm meter,to measure the specific resistance of each coil... what each resistance value is per coil,,i dont know,,,also,,,a simple check with a continuty tester will tell you if theres a break in one or more of the coils,,,im not sure how the coils work in series,,somethin like if the 12 volts has to go thru 2 is med..all three is low...none at all its high(no resistance) but im not exactly sure of that,,just common( electrical) sense

markdtn

Usually what you describe is a bad relay. Try bypassing the relay and see if the lower speeds come back. If not it could be the resistor. You can get them from Dr Rebuild, 9220414. Don't think Radio Shack has any heavy enough.

Ganey

I have fixed way more than my share of these. On Chevys they are not normally a problem.

1 Easy, look for a break in any of the Very easy to tell.

2 Look for an electrolytic build up on the resister coils- this can be broken off by carefully using needlenose pliers.

On some if not all of our C3s, 2 fuses are shown for the blower (High & Heater/AC)
You need to recheck the Heater/AC fuse & contacts.
Simply rotating a round fuse can clean the contacts & fix.