Whenever i turn my heater on, no matter what, while idling, my rpm's flutcuate and when driving, my power surges. I was looking at the truck, and what i have realized is that when my heater is on, my A/C pump turns on and off. It is like i am switching to A/c, then turning it off inside the truck. Does anyone have any idea as to why this would be happening.
Thanx,
-Shawn-

 

Some settings on the heater controls operate the A/C ....Defrost , Floor / Defrost & Max will run the A/C . Cold air is able to support more moisture so it helps speed up defrosting / windsheild moisture removal .

 

I may have some insight on your questions. The reason you are having fluctuating problems when you turn the heater on, is your charging system is warn out, by that I mean your alternator cant keep up, and its only a short matter of time before it dies altogether, it cant charge your battery and that’s why it fluctuates. You can test to see if your alternator is bad but you need a tester and its sort of confusing, I’ll just tell you the easiest way of testing, take it to auto zone or something of the like, and have them test your alternator with a portable tester its a big thing on wheels and they can test it without taking out your alternator. Or you can take out your alternator and have them test it inside this way is more accurate. And best of all they do it for free.
Does it get worse if you have the lights on and the heater?
Do you sometimes have trouble staring your truck like turn over slowly?


To why your A/C is going on when you have the heater on, this perfectly normal. When your put heater on defrost and you normally do this in winter when you don't use your A/C, the compressor for A/C goes on for a couple seconds or longer. Now the reason it does this is to keep road grime and dust out of the clutch and keep it clean. If the compressor does not do this it may go may cause death to your A/C system. It will only go on if you have a refrigerant in your system. And once the system loses some refrigerant and goes below a cretin level it will not go on, and you may to recharge it.

 

The problem doesn't really seem to get worse with the headlights being on, or not that i noticed, i will have to watch it more closely. As far as the motor turning over, it turns over pretty strong, but i just put a new battery in. I guess that i should pull the alternator and go get it tested, it is starting to make some funny noises.
-Shawn-

 

[updated:LAST EDITED ON 19-Nov-01 AT 04:17 PM (EST)]
Both of my F-150's volt guage fluctuates alot when the headlights are on. Normally it's about 13-14 volts and with headlights on it's about 11 or so.




'93 F-150 loaded and modified!

Several other project vehicles

 

 

you might have the a/c system checked it coming off and on sound like you have low refrigerant level. it is normal for it to come on but it should not flucuate like that unless it is low on refrigerant.