i have a 2000 blazer ls. when i turnto one of the3main a/c settings it struggles to get up to speed and seems to have little power, but is fine when the a/c is off. it also does it when i have the heat turned on one of those three settings. also the three setting i'm talking about are the a/c, max a/c, and having it on your face and legs. any ideas?

 

The AC makes sense to an extent because it's another strain on the motor to run it. Obviously, the more belts you start running off of that motor, the less power that is actually going to make it to the wheels. However,I thoughtthat the engine heat was vented for your HEAT controls. So, that wouldn't exactly coincide as an understanding to your problem.

Could you describe how much the truck is hurting for power while you're running the a/c?

 

You'd expect power drain to a certain extent. If it is significant power drain it means that you may have a bad bearing on your compressor,or else the A/C systemis low on oil; thusincreasing friction. Do you hear any kind of roaring or squealing noise when A/C is engaged?
All three settings, (A/C, Max A/C, and Bi-lev) you described are A/C settings and the compressor should engage when switched to those settings, even if the thermostat is turned all the way to heat.