Switch going on/off during idle

FunInTheMud · September 14, 2001

Hey Guys,

Every morning I go out and start my truck up. It is about 50 degrees outside when I do it. When the engine is idling, I hear a switch going on and off. When it does, the engine idle will change. You can even see it change on the tachometer. It won't do this when it is warm out. Is this normal, or is it suppose to do that.

Shaners · September 14, 2001

You're not running the defroster to get the dew off the windows are you? If so you hear the compressor for the A/C kicking in and out. It takes a fair amt of HP to run the A/C so you'll hear it drag the motor down when it kicks in.

Smitty00Z71 · September 14, 2001

that's what I would say, has to be the compressor

Quote: from Shaners on 5:11 am on Sep. 14, 2001
You're not running the defroster to get the dew off the windows are you? If so you hear the compressor for the A/C kicking in and out. It takes a fair amt of HP to run the A/C so you'll hear it drag the motor down when it kicks in.

FunInTheMud · September 16, 2001

Hey Guys,

Yes, I am running the defroster when the switch goes on and off. Today I tried it, and sure enough, it is the compressor going on and off. Why does it do this, and is there any way to disable it. My defroster hasn't been working right since I bought the truck. When it is cold out, it will take about 10 minutes for the air come out at the top, but when it is warm out, it will work fine. I took apart the motor arm selector and rebuilt it, but that didn't help. Any suggestions on how to fix this?

FunInTheMud

Shaners · September 16, 2001

I don't think you can disable it... The compressor comes on in defrost mode (in temps above freezing) to help get rid of the moisture in the air which aids in getting the film off the inside of the windshield.

If I had to guess about your problems getting the the air to come out of the windshield dash vents... I'd guess you have a vacuum leak... The older trucks (and cars) had vacuum operated "air diverters" (since I can't remember what they are called).

FunInTheMud · September 16, 2001

Shaners,

Thanks for the input. I don't think the defroster works on a vacuum line. There is a little black motor near the accelerator pedal that is electronically controlled by the heater & A/C unit. There are two spring-loaded arms that are attached to the motor. If I pull back hard enough on the one arm, I can get the air to come on at the top. But, if I do that all of the time, I will break it. Whatever the problem is, it is thermal. Thanks again Shaners!

FunInTheMud

Shaners · September 16, 2001

don't give up yet funinthemud...

We've got a couple of guys here that have had their dashes apart and know the workings of the defrost system in the old body style trucks better than I do...

They may know a quick fix for you...

(Edited by Shaners at 1:22 am on Sep. 16, 2001)

FunInTheMud · September 18, 2001

Hey Guys,

I talked to a couple of people today, and they all think it is a vacuum problem. The thing is, I don't think I have a vacuum setup. There is a set of wires leading into the htr/ac actuator that look like there are electrical, however someone told me that they should be vacuum lines. The motor inside actuator should require electric, not vacuum, right? The funny part is, the defroster works perfectly when it is warm out. It is just when it is cold out that it will take about 10 minuets to come on. You can hear the blower motor turning, but the air is not coming out at the top. Then, all of the sudden I will hear a "pop" and it starts to come out at the top. I think it's time to take it to a mechanic, I give up.

FunInTheMud