on my 04 ,monte when I put on floor heater the a/c clicks on..if its under 40..which its supposed to do it does not..I have the snowflake button and its off..a/c goes on with defrost..which its supposed to..why would floor heat cause compressor to click on?

When you turn to the "heat" position, the A/C clutch should not engage.....but in defrost it will turn on.....it will not turn on if the ambient air is below 40F.....

ok why is it going on above 40? any ideas?

I assume you have a manual system, and not an automatic one....

Do you have a button to activate the A/C? For example, when you have vent mode on,,,there should be no A/C....if you press the A/C on button it will come on? Does the A/C button light up when this happens?

If it does, does the light come on when you turn to floor/heat mode?

Also, depending on the year, if your recirc button is on, this may turn the A/C on also....

yea the snowflake button is off,its not on recirc its an 04 monte..the a/c works on vent mode..if I click the button one click to the left its like mix floor and vent the ac goes off..its like a in between position..

The PCM turns the A/C clutch on, as long as it is getting a good pressure signal from the pressure sensor(when temp drops below 40F, the pressure will also drop)....but it must get a Class II input from the A/C control head, to turn the clutch on......could be a control head problem....here is where a Tech II is invaluable.......it will tell you if the head is sending a request, when it should or shouldn't.....

will get scan tool on it tomorrow..