GM a/c query

05 trailblazer. Dual zone heat/cooling. I think truck has rear a/c too. A/c works so-so on pass vents. Works less so on driver vents. I added 12oz of freon and pass side is noticeably colder but driver side is only a touch cooler/better. The receiver under hood is not cold at all. Inlet/ outlet lines are both warm. Compressor seems to be on 75% of time. Belt driven rad fan. I think receiver should feel cold if pass vent is cold? Recv lines are not sweating with 80f air temp

There are temperature/pressure charts to enable safely topping off an AC. And a good working knowledge of the AC system would be a great benefit. The television ads would have you think that the $20 can with a gauge and release valve will give the DIYer all that a professional has but that’s far from the truth.

Get a manifold gauge set and google for instructions for your vehicle. What you don’t know can make you dangerous.

Rear A/C vent from the console doesn’t necessarily mean you have a rear evaporator. Look under the hood for Freon capacity. About 2 lb means no rear evaporator; about 3 lb means you do have a rear evaporator. I’d be tempted to throw another can in it and see if the receiver gets cold.

Found out trailblazers are known for funky vent/dash elec actuators which are also used on hot/cold blend door functions. U disconnect battery and actuators basically adjust/calibrate and die. Driver side has 1 motor and pass side has 2nd. I think pass vent is 48f while driver vent is 60f. The receiver is warm. The receiver/accumulator pipes are warm.

After spending many hours at found it was common for an actuator to fail after a battery was disconnected. I always use a memory maintainer, of some sort or another when doing procedures that require disconnecting the battery.

I think most silverado/tahoes of this era use the same blend door scheme. I don’t own either so perhaps it is common for blend door issues when the battery is unhooked? Who knew? Vent controls die when u unhook battery.

I disagree with the theory that disonnecting the battery is the cause of blend door problems

We have hundreds of that era Silveradoes, Tahoes, etc. in our fleet

We have replaced no blend doors at all, as far as I know

But we’ve replaced plenty of batteries

My sample size is good

I agree wholeheartedly with Rod’s first paragraph, but I would suggest simply taking it to a shop that specializes in automotive A/C systems. The proper test equipment and knowledge is essential to getting an A/C system working properly. The system will probably have to be evacuated, tested for leaks, leaks repaired, and be recharged… as a minimum. A part may need replacement, but I’m guessing that won’t be the case.