I have a 2003 Chevy Trailblazer and it with AC issues!

Smart man using a scanner for the actual temp. Assuming you're not losing coolant....2 things I'd look at here, 1st is you may have air in the system, make sure to purge all the air. 2nd is your fan clutch, I've replaced a few fan clutches in my own Trailblazer. Have had them bad right out of the box brand new. Have had bad brand new fan clutches on 2 of my last Trailblazers. You should hear it engaging especially in stop and go traffic.

The throttle body needs to be cleaned, grime in this area prevents the throttle plate from closing completely and allowing air to enter, making the air/fuel mixture lean. Make sure to clean the front and back sides of the throttle body. Also, disconnect the battery during the cleaning process to allow the computer to reset and relearn to the cleaned throttle body.

think you have damaged the heating control computer from the sound of it

Hi. There happens to be a common problem with these trailblazers inside the ducting box located under the dashboard. The mode actuator door motor stops working due to a faulty motor itself and the default position is defrost only. As far as the Air Conditioning not working, there maybe another problem to diagnose there. Could be low refrigerant, or electrical problems to the compressor, or faulty fan clutch(another very common problem with these trucks). Type in mode actuator door and 2005 trailblazer in your search engine online i.e. Google or Yahoo and you will find many posts about this problem. I think there may even be a Youtube video about replacing it. Let me know you need more help. Thanks.

most likel blend actuator if ur temperature gsuge is hitting up

The first thing you need to do is clean the throttle body. This area of the air intake gets dirty and gummed up and prevents proper air passage. While the cleaning is taking place, make sure the battery is disconnected so that the computer will be reset and be able to relearn with a clean air intake.
Next, you need to have the AC refrigerant checked, it may low. OR, the low idle speed because of dirty throttle body just does not allow the compressor to produce enough pressure.

It is probably just your air conditioning. If you have your defrost on it also runs your ac pump. So if you have your ac or defrost on and you shut the vehicle off you will hear a hissing noise for about 10 seconds or so which is normal.

{: ) Check first the fuse labeled HVAC1 10A at the rear fuseblock. If okay, the mode actuator could be faulty. You can try this: turn ignition switch and a/c off for a minute. Then turn ignition on, wait forty seconds. Afterwards, start the engine, and check your a/c again.

Could be your main blower motor resistor, mine would still run the fan even after shutting off the vehicle.(safari van) Had to unplug the resistor to stop the fan,it was near the blower under the hood. Bought a new one for about $45 bucks. Replaced it and all is fine. Might want to check relays first, sometimes they stick and need replacing.
Good luck.

sounds like you have shorted the a/c cycle switch. when you do this it wont cut the clutch on the compressor this is located on the a/c drier on the fire wall hope this helps you and good luck !!!!