Blower switch question

[pickupman]

Since I got my A/C fixed 2 weeks ago, and actually been able to enjoy it, I noticed that it seems like the blower is only running at two speeds. According to the manual it looks like I should have a Low, Medium and High speed. Well, I know for sure it runs at the low speed, and the medium speed works too. When I switch it to "High", I don't hear any change in the blower speed. I can't remember if I tried running it on the High speed at all, so I have no idea if it already wasn't working or not. The systems is cooling so well I only really need to run it on Low.

I've been told that I have dealer installed A/C, so I don't know if that makes any difference. According to my manual, it sounds like if the resistor were to go bad, it would only operate at the "High" setting, because at that setting the resistor is bypassed. That has me thinking maybe the contacts on the blower switch are bad. The service manual does list some diagnostic procedures, but nothing specifically for the problem I mentioned. I am not that good with electrical stuff so I was hoping someone can point me in the right direction.

 

[ryanecvbrown]

You're correct, the resistor pack on the blower motor on the passenger firewall is working if you have variable speeds on your HVAC fan. The resistor pack has three coils woun to provide resistance in the fan circuit which in turn controls fan speed. I'd start by pulling off the dash cover and pulling out the HVAC dash control. Look at the terminal on the back I the fan speed switch. With age they tend to get hot and melt, screwing up our fan speed control. If the terminal looks like it's been getting hot or is already melted, replace the switch and install a new pigtail on the wiring harness if the wires aren't damaged. Corrosion on the terminals or in the wiring could be a culprit too.

 

[laserjock]

I thought the resistors were notorious for burning out but if I recall that gives you only high speed. Maybe I'm mis-remembering.

 

[pickupman]

I thought the resistors were notorious for burning out but if I recall that gives you only high speed. Maybe I'm mis-remembering.

That is my understanding as well, although I have read that with some resistors, they can lose speeds one at a time. I don't know if the resistors in our trucks would fail like that or not. If they do, I might actually have a Low and High speed instead of Low and Medium.

I will definitely start by testing the switch, and it probably wouldn't hurt to take a look at the resistor and clean out the blower fan, as I hear that they can accumulate enough kindle to start a fire. I have almost never used the HVAC system since I got the truck 4 years ago. It never really gets cold enough in California to use the heater and I've only had the A/C working for 2 weeks now.

 

[ryanecvbrown]

Yes, the resistor pack controls the first three speeds, when the fan is on high speed you have take the pack out of the equation and providing fullpower to the blower motor. If your first three speeds are workin but high speed is lacking in oomph the switch and/or wiring could be the source of your problems. If you're gonna clean out the resistor and blower housing, might as well clean out the motor with compressed air while your into it. Can't hurt!!