climate control question

travlindude

It seems like my problem started out with a clicking under the hood, then I replaced blower control module, then the compressor stated "grunting" when the clutch engages, after 2-3 grunts it runs until the low pressure cutout takes it out at 28#. I have also replaced ambient air temp sensor, this am and still no ac or heat will come on inside the chev. Yesterday I raised the low pressure to 31# and the compressor will stay running after it quits grunting 2-3 times. When I could get the compressor to run it would make cold air, with the higher pressure the evaporator fan would run, and the grunting noise was worse. For the outside ambient temp the low side should be 30-35 and the high side should be 180 which is the reading I have, which leads me to believe the valves are not broken in the compressor and it turns easily when turned by hand, so I doesn't seem to be the problem.. If the expansion valve/line strainer were clogged due to the dryer desiccant failure my reading would be way off, from what they are. If I could figure out what the clicking noise is, & if it's part of the AC, or the grunting I could get this climate control system back going. Any suggestions, I realize this isn't much to go on but I'm at a loss. Am I missing a hidden valve in this system, that I didn't learn about in HVAC school 40+ years ago.

imidazol97

I'd remove the fuse for the compressor at least for testing. You should be able to operate the system inside the vehicle and get heat, as well as to modulate the amount of heat. Otherwise you need to find a diagram of the HVAC box and start looking for the various control motors that move the vanes to change the air direction, mode door, change the blend door to vary the amount of heat, and change the air input source to get recycled air.

Is it possible the clicking you are hearing is one of those electric motors trying to operate inside the vehicle?

Is your compressor a variable compressor? I thought GM had gone to those in most applications. That might not include trucks...

As to the compressor, not knowing what has been done to the system and if something has contaminated the freon, I'd fall back on the info about the GM compressors which are usually variable. If you're getting unusual noises from the compressor and it occasionally seems to provide pressures that can give cooling, I wonder if the problem is in the control that changes the amplitude of the movement of the compressor pistons.

The variable compressors are very difficult for home guys to determine the state of charge even using the low and high sides. The best technique is to completely dry the system with the vacuum, and refill with the prescribed weight of freon. Then the charge level is known.

My next step were I you would be to take it to a quality shop that _knows_ AC for all models or take it to a GM dealer that has a specialist.

I don't know how to tell if your compressor is variable. An AC shop will likely know without looking. It may vary with the engine in the vehicle and the options such as dual auto control AC/heat.

Compressors are listed in rockauto and acdelco.com. It appears there were changes to the compressors used during the production year from what is given on the Acdelco site.

http://parts-catalog.acdelco.com/catalog/catalog_search.php

travlindude

I would like to add that for the first time the clicking as started with no HVAC running. I believe it's not related to the HVAC. My vehicle is a 07 chev Trailblazer with 112000 miles.

travlindude

Thanks, I appreciate your info, I have done what you suggested to the compressor, I've evacuated the system and refilled with the proper amount. I'm checking the damper doors for proper operation, and through this processor I pretty sure I have found a bad blower motor control module. Still working on this ac......