I'm having an issue with my A/C and before I tear the truck apart I wanted to see if anyone had seen similar issues. My truck has the dual zone controls. I normally leave the paasenger side truned off, so one control for the cabin. The A/c compressor is coming on and cycling, the fan is just now blowing.

It started with the A/C fan speed varying at lower blower speed. If it was at 2 or 3 bars the blower fan speed would surge. Most of the time I either run it at high to cool it down on inital start up, or run it at 1 bar and the temp at 60 to keep the truck cool but not blowing like mad.

The problem then moved to the high speed where the fan would vary at high speed. It has now moved to where the fan will not come on at all. If it does come on, the speed varies quite a bit, and then it will just stop.

In talking to my buddy at the dealership he recomended replacing the negative ground as they have had a lot of weird issues that come back to the negative ground being bad on trucks and not supplying the correct voltage to the ECM, and the BCM.

Right now, as I said, the A/C compressor is coming on, the system is getting condensation on it. The fan will come on intermittently which indicates to me the fuse is not blown.

So, my guess was the negative ground as suggested, the blower fan itself, or perhaps the A/C control unit. But, before I shotgunned a bunch of parts I wanted to see if anyone had any similar experiences to see if they had a resolution.

 

try doing a voltage drop across that ground, see if theres any resistance
but i'd start looking at the blower motor resistor cause it sounds like everything except the fan is working

 

I just went thru that exact same thing with my 08 VMax.
I needed to save my money for new struts/shocks, so I took it apart.
I took out the blower and blew it out with a blow gun and the bearings seemed a little stiff so I tapped the shaft a couple of times and it spun easier, so I put it back in. I looked at the resistor and all of the connections, and they all looked fine, so I just blew the dust off and made sure the connections were tight when I put it together.
That did the trick and it has been working fine for about 3 or 4 weeks, and my ac is always on here in Central Tx.
If it quits tomorrow, I think I'll buy a new fan motor, first.
Take a look at it, its pretty easy to get to.
Good Luck,
Jeff

 

My blower went out twice on my 2007 avalanche. It's very common with these vehicles. At first my connector melted then my blower motor went out a few months ago. Could be a resistor too.

 

On these trucks they use a variable speed blower motor control module mounted by the blower motor that has a pigtail coming out of it and plugs into the motor.

Unplug the pigtail going to the blower motor and set the control on high and see if you have full 12-14V coming out of the module and then punch the blower down button one step at a time and verify the voltage falls accordingly. If you do not have the correct voltage in high speed the module probably failed. But be forewarned usually the motor starts to die and pulls excessive amperage and nukes the module. Usually when I have problems I replace both the motor and the module to have a bullet proof repair.

The motor will show a full 12V if you probe from chassis grd to purple coming out of the module. The module digitally varies the amount of ground allowed to the motor to allow for a PWM controlled speed.

THESE TRUCKS DO NOT USE OR HAVE A BLOWER RESISTOR