The A/C- heater blower in my Avalanche only works on high. I set it one through 4 and nothing happens. If I set it on high-5- it works fine. Any idea how serious this is?
resistor block open internal,
Two things can cause no low blower speeds. Either the fan speed resistor board is defective, or the high speed fan relay is defective.
high speed fan relay? it works ,as the man said , works great on high speed ONLY. tells me the field is being created the contacts close and the mtr operates.look at a diagram,and you will be enlightened to know the resitor blk is by-passed,during high speed operation.
Replace the blower motor resistor block.
The high speed blower relay switches the voltage to either the resistor board for the low speeds, or switches voltage directly to the blower motor for the high speed.
The same thing happened to my Silverado - it’s the resister block that has a separate resister for each fan speed - the ones that you are missing are the ones you use all the time, so they burned out. The part is not expensive - I thing mine cost about $40.00 - but you may only be able to get it at the Chevy dealer. The new part seems to be made better than the old one. You can replace it yourself if you don’t mind lying on your back and removing the plastic cover from the heat ducts under the passenger side of the dash. Removing the cover and putting it back is the hardest part of the job. The part is located in the heat duct and is held in place by two screws. The wires to it end in a block plug with a locking clip holding it in place - release the locking clip so you don’t wreck the block. While you are there, you might as well replace the cabin air filters that are there - you will be amazed at how much crap is in those filters.
If all the four speeds went out at the same time, then the relay is likely the problem. If they went out one at a time, the more common problem, then it is likely the resistor block.
I just checked the www.rockauto.com web site, and they may have the resister block for you vehicle - after putting in your year, make & model, look under heater parts. I have ordered several parts form them, and their prices are OK. They have stuff that my local parts place doesn’t have and can’t get (like replacement tail gate hinges for my Silverado).
Thanks. I will try it.
im not going to get into the other posters argunent but will say you need a resistor,seen it to many times