a/c comes on with heat
 

Hi everyone new here,

I have a 99 sable that the a/c comes on with the heat. When I turn the control to defrost, floor, defrost/floor etc. with the knob turned to hot the a/c compressor and radiator fan turns on. If I turn the control to the cool side everything cools down correctly. But if I turn it back to hot it blows out luck warm air because both the a/c and heat are working. If I turn it to just the vent position and hot I get good warm air. So my question is why is the a/c coming on with the heat. I can here the door open and close under the dash so that seems to be working.
I did just change the metal line under the hood next to the fire wall that connects to the heater core they had a hole through them. Those lines are nice and hot so the heater core isn't plugged. I don't know if this was already there because it's my wifes car and I don't drive it all the time. Any help would be appreciated.

Tony

The AC compressor should be on for defrost and mix but off for floor. There is probably a relay sticking or some such nonsense. Do you have the manual temp system or the automatic temp system (sounds like you have the manual one). I'm not sure how the controls tell the compressor to engage or not for a certain setting, but it sounds like it's not working right on the heat side of things.

I believe it's the manual control, has three knobs.

is he right or is he right

I do have the manual controls. I haven't drove the car since I replaced the heater hoses. The wife tells me everything seems to be working correctly. I guess I will wait for colder weather.