OER Parts offers a wide selection of Air Conditioning and Heater Parts for your 1978 GMC Truck. OER Parts offers 1978 GMC Truck AC Parts, 1978 GMC Truck AC Systems, 1978 GMC Truck AC and Heater Controls, 1978 GMC Truck Heater Parts, 1978 GMC Truck Air Conditioning and Heater Hoses and Parts, 1978 GMC Truck Air Conditioning and Heater Vents.