Strange HVAC Blower Issue

[DA BIG ONE]

I have a problem w/blower motor not staying on high when I first AC start system. It will go to high, then change between speeds for a little while usually while driving around town then be ok. Time lapse for this problem varies.

I checked alt (105 amp unit) output 14.3+ volts, amps are 40+ at idle then with load applied it jumps up to 60 even 80 depending on load. I'm suspecting alternator.

Truck starts fine, runs great.

Any thoughts?

[DChristie]

I have a similar issue, only I can't get medium high from my blower. I've tracked it to the switch on the dash. I just need to repair or replace it now. Time time Time :(

DChristie

[DA BIG ONE]

Originally posted by DChristie:
I have a similar issue, only I can't get medium high from my blower. I've tracked it to the switch on the dash. I just need to repair or replace it now. Time time Time :(

DChristie Thought it was the switch too, but it is a few months old.

[DmaxMaverick]

In most cases, HVAC problems on late model vehicles can be caused by the blower resistor module. A failing module can cause the fan to cut in/out, and in most cases, you just loose certain blower speeds. It is very rare the switch actually fails, but could happen. The resistor modules are the easiest part of the system to replace, and are usually the cheapest. They are also a known weak link.

Another thing to consider...Is the fan speed actually changing? When your HVAC system switces between fresh/recirc modes, it may appear the blower is speeding up or slowing down. Ambient temp, cabin temp and actual system pressures will cause the system to switch between the modes without any input on your part. Another known issue with this series of HVAC systems is the loss of control due to breakage of linkage, usually the door actuator near the APP module.

[JohnC]

Don't know if this has any bearing on your problem or not, but if you select max cool or recirculate, the AC control will switch from recirculate to fresh air automatically if it senses conditions are ripe for a freezeup. This sounds like the fan is switching speeds even though it isn't really. I understand a low charge can increase the likelyhood these conditions will be met.