A/C Fan Switch

[Rodd]

My A/C fan switch when turned off stays on low and med/high and high is high but when I hit a bump med/high and high some times shuts the fan off until I hit another bump and it turns back on. Is this the switch or the A/C heater fan resister? How do I diagnose which it is?

 

[Rodd]

this is on my 98 suburban.

 

[FellowTraveler]

I suspect the fan switch is damaged "usually melted" it is replaceable, however the cause is excessive amp draw along with poor ground to blower motor which may lead to a melted harness too "the switch fails because of it's terminals heat up melting the plastic housing." While it may sound like a big deal to fix it's really not and GM sells a repair kit to do it...

 

[WarWagon]

In depth info on that switch/problem here: http://www.thetruckstop.us/forum/th...ers-w-blower-off-erratic-or-no-airflow.28385/

 

[THEFERMANATOR]

The fan swicth actually burns out from years of powering the a/c clutch. On a 95+ there is a bank of relays behind the glove box, on top of the evap box, and to the left that handle all the power to the blower motor. For some reason GM left the A/C clutch current going through the blower switch and pressure switches, hence why they eat low pressure switches so often in these trucks. The blower switch is serviceable seperately from the control head if that is your problem. Grounds, grounds, grounds, did I mention grounds are CRITICAL for the A/C unit. Around 97 or so GM changed the grounding system to the evap and imp[roved it, but it doesn't hurt to double check them to make sure they are good.

 

[Rodd]

Thanks guy's just got back from vacation and time to get this solved.