I had a new American Standard AC compressor and evaporator coil installed, keeping old gas heat system. When I switch from heat to AC a foul odor (like burnt hair) is so strong that I turn off the AC and open windows to air out the house for a couple of hours. Then AC works fine. When I switch back to heat, then switch to AC, the foul odor happens again. Both Heat and AC systems seem to work fine except for the foul odor smell. Any ideas what may be the problem. Thanks.