'01 Aurora A/C won't turn on!

[pwfootball]

I have just recharged my 3.5L Aurora with R-134a and had a mechanic look at my A/C system, the lines are cold and seem to be working properly. When I turn on the A/C inside the cabin I can hear the clutch engage on the compressor but the system only blows hot air. I believe the system is stuck on heat somehow because I cannot blow vent air either. What could the problem be? How can I fix this? Thank you

[RJPolds]

How did you recharge a/c without the a/c on in the first place?

[pwfootball]

The compressor works and the lines run cold but somehow the ventilation system does not switch to blow the cold air inside my cabin. There's something in the ventilation system that may not be working correctly, I checked all the fuses and they are good.

[RJPolds]

hmmm. i do heating and cooling for a living.

I need to know the answers to these to help ya better.

How much 134a did you put in it? How much does the car suggest.
What are your running pressures at?
Was the system completely dead before you added or was there still 134a still in it?
If it was completely dead before you added, did evacuate the lines with a vacuum pump?

There can be many varibles.

[pwfootball]

The system was completely out of 134a and my mechanic evacuated the lines and added a can which was enough to activate the compressor. I let this stay in my car for 4 days and the mechanic checked the psi to make sure nothing leaked over time. He then added two more cans (sorry I don't know the amount in ounces) which is what this particular system requires according to my mechanic and trusting his knowledge he confirmed to me that it was running at the correct psi. My mechanic couldn't figure out what was wrong with the A/C because everything worked except my ventilation only blows heated air and doesn't switch to vent or A/C. He thought it was someting electrical that should be looked at by someone specializing in this area.

[RJPolds]

Well all cans of 134a are 12 ounces. So he added 3 cans total, which equals 32 ounces. 16 ounces to a pound, so have 2 lbs. of 134a in it. Usually, a car only takes about a 1 1/2 pounds. Check under the hood. there should be a label that says how many pounds of 134a is needed.

An overcharged system will not blow cold air even if your lines are cold. That is why knowing the operating pressures on a nice warm 70-80 degree day is needed.

If this is not the problem, then I would say that, your right. Something electronically or something is not allowing to switch over. Your best bet would be to take it to a A/C specialized shop.

[95supreme]

Check the wires going to the compressor and make sure they aren't corroded. also, check the ground wire on the compressor too. GM made a mistake by making the ground wire too short, and not grounding properly. This can cause the AC to not turn on.

[RJPolds]

if his lines are getting cold, then his compressor is running.