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.

((had a new American Standard AC compressor and evaporator coil installed, keeping old gas heat system))

First step
Call the people who put your new equipment in. You paid them to do a job and they should be the first in since they were the last out.
Sounds like you have dirty sock syndrome
They will have to clean and use a special coating agent only available to professional HVAC mechanics to seal the new coil surfaces to further prevent the odor.