in my 2000 gmc jimmy, I have noticed that when i turn my "Heater controls" to anything other than off the engine has a hesitation while accelerating. If i put it on A/C then i would understand cause of the extra load from the compresor. But when i use the heater weather it be on the floor, vent or defrost, the engine hesitates while accelerating, and i have to freeze my butt off till i hit highway speed. and this happens weather the engine is cold or at temp.

And i dont know if this is related to my problem, but when i do have it off i notice air is coming out of the floor vents. The faster my speed the harder the air blows out of it. Noticed it one day on my way back from work when my foot flet like it was on fire, lol.

I know theres other threds about hesitaion, but i havent noticed any being because of the heater use.

 

Check and clean all grounds !!!

 

Possibly a vacuum leak as well, I had an issue that when I had my ac/heat on it would go through all vents... Found that 2 separate hoses were disconnected one on the drivers side and one on the passengers side.

I too had a slight hesitation, but it was nothing major. Just noticed that it would almost skip a beat.

How bad is yours?

 

plus most functions mix in a/c if you look close at the dial. the compressor will be on with ant defrost or a/c mode to dry the air, it annoys me too. +1 on weak vac but the a/c compressor eats some ponies

 

You can eliminate the compressor by pulling connector off the accumulator bottle.

Airflow is supposed to stop in off position. Blend door cant stop airflow from the cowl
What happens when you switch to max ac?

Most likely you have a leak in an actuator diaphragm or a line that's loose.

Under dash, engine running, listen for hiss in all positions.

 

I would think you would hear the vacuum leak !! but not sure !! i did hear my heat/ac control leaking and i replaced that ,it sounded like a hissing noise