We have a ground source heat pump which heats and cools our house. We notice a very distinct smell of "grease" when the air conditioner runs. It cools so we have been assured that the problem is not in the condenser. We do not notice this smell when it is in the heating mode. Any ideas?. JudyNTom in Montana

Since you only smell this odor in the cooling mode I might suggest you check for proper drainage of the drain line and condensate pan in the air handler . I say this because the big difference between the air conditioning and heating is that there is only condensate during the air conditioning mode and none during the heating mode. I would suggest washing the evaporator coil and check the drain pan for proper pitch to insure that it does not hold water, this could be a mildew odor, hope this helps . Mike