I have a 2004 gmc envoy and when you connect the battery back and turn on the ac or heater the car turns off.do you have to reset something...it will go away but after a while..

You probably unhooked the battery recently if this just started. Classic dirty throttle body syndrome. Unhook the battery, yank the throttle body off (only 4 bolts) and clean with a product like a sensor safe Seafoam and a rag, do not use wire brush or something abrasive, will damage the aluminum. Can re-use the hard plastic O-ring many times over. Hook the battery back up and drive around for 15 minutes or so. This is THE most popular problem with Envoys and Trailblazers. After the original battery was unhooked, the computer thought the throttle body was clean, which it is not, so you will have idle problems when the A/C or Defrost is on. Before you unhook the battery for cleaning, make sure you turn OFF all HVAC including AC or Defrost, or you the vent actuators can go bad on you.

Throttle body needs to be cleaned front and back. Disconnect battery while doing the cleaning to force PCM relearn.

sound to me like a manifold vacume problem. your enviroment control is ran by vac and vac leak or low vac will create a stall condition. ck vac. at switch at heater core box. you will notice a vac line that moves the flap to cover core,for ac, or open for heat
,if no vac, ck firewall in engine compartment. you will see a vac line that travels thru the fire wall .trace back to source checking for cracks and breaks.

Bad Compressor bogs down engine and stalls

The throttle body needs to be cleaned, make sure to clean both the front side and back side, this means that the throttle body needs to be removed from the intake. Also, disconnect the battery while cleaning, this will reset the computer and allow it to relearn to the cleaned throttle body.

You need to have the throttle body cleaned. Make sure that both the front and rear sides are cleaned thoroughly. Also, the battery should be disconnected while the cleaning is done, this will reset the computer and allow it to relearn to the cleaned throttle body.

2004 Envoy xuv 6 cyl when I turn on the A/C the truck stalls but as long as I keep my foot on the gas it will continue to run

Sounds like ac compressor is dragging.It might be that rpm is to low also.Step on the accelarator and if you have a tach bring rpm up to 700 to 800 in drive which is were it should run with ac on. With ac off rpm should read around 600 in drive.

problem with ac compessor most likley when in defrost mode ac compressor will be working creating a major load on engine and cause it to stall

The way to fix this is by changing the blower motor resistor.
I paid $138.00 at the dealership for a new one and it solved the problem.