GM Service Manual Online
For 1990-2009 cars only

Inspect the heat output of the heater system with the following procedure:

Preparation

With the engine sufficiently cool, remove the radiator cap, start the engine, and allow the engine to idle. Set the heater controls to HTR mode, full Red (Hot) temperature, and HI blower speed. When coolant flow in the radiator is visible through the filler neck, install the radiator cap.

Temperature Check

When the engine is warmed up (after approximately 20 minutes of operation), drive the vehicle. Use an accurate thermometer in order to determine the outside air temperature and the temperature of the air discharged at the floor outlets with the vehicle being driven at 48 km/h (30 mph). Minimum acceptable heater output temperatures at four different outside air temperatures are shown in the table below.

Outside Air Temperature

Heater Air Temperature

-18°C (0°F)

54°C (130°F)

-4°C (25°F)

59°C (139°F)

10°C (50°F)

64°C (147°F)

24°C (75°F)

68°C (155°F)

Minimum acceptable heater output temperatures for outside air temperatures other than those shown can be approximated by using the Fahrenheit scale and rounding off the outside air temperature to the nearest 5°. For every additional 5° of outside temperature, an additional 1.8° of heater output temperature should be allowed when the outside temperature is below 50°. An additional 1.6° of heater output temperature should be allowed for every 5° of outside temperature when the outside temperature is above 50°.