[GMC Jim]

GM used 2 different motors with their heater and air conditioning systems... The heater only system used a blower; specs are:-13.5 volts; 8.25 amps max; RPM 2550-2950 max. The blower used with heater/air conditioning system; specs are:-12 volts; 16.5 amps max; 3700 RPM minimum. The air cond systems used a relay which controls the blower high speed selectiom. This relay is located inside the firewall; near the top right rear of the glove box. If this relay is not operating, there be no high blower speed. This can be checked by jumping a wire from the postive battery terminal to the blower wire which should be accessible near the blower on the engine side of the firewall. If the speed ( and output) imcreases as compared to the high blower switch position on the air cond. control in the cab; then the relay is not operating. Check for proper grouinding of the relay as this is a fairly common cause for malfunction