A/C - Reduced Heater Performance
88chevy25GMC NUMBER: 88-T-177
GROUP: 1A - Heating and Ventilation
DATE: November, 1988
CORPORATE
NUMBER: 861105
SUBJECT: REDUCED HEATER PERFORMANCE
MODELS: 1988 C/K EOUIPPED WITH EITHER DELUXE/HEAVY DUTY HEATER (C42) OR AIR CONDITIONING (C60)
Some 1988 C/K trucks may experience reduced heater performance due to a missing separator in the heater core. If a vehicle exhibits this condition and the VIN of the vehicle is within the breakpoints listed below, the following diagnostic procedure should be used:
1. Run the vehicle until the thermostat opens. The vehicle must be at normal operating temperature.
NOTE: This may be accomplished by (a) physically driving the vehicle to achieve operating temperature or (b) letting the vehicle idle in the service area and visually monitor the coolant flow or record the coolant temperature using a thermometer via the radiator cap opening. If method (b) is used, it may be necessary to block off the radiator to restrict air flow to aid in achieving operating temperature.
2. The remaining procedure must be conducted at 60~-80~ Fahrenheit ambient temperature in order to properly diagnose the heater core performance.
NOTE: Conducting this test at 60~-80~ Fahrenheit, will insure proper performance of the heater core in cooler ambience.
3. Set control to HEATER mode.
4. Set fan speed on HIGH.
5. Engine speed at IDLE.
6. Check the vehicle heater outlet temperature for several minutes with a thermometer.
NOTE: The outlet temperature should be a minimum of 50~ Fahrenheit higher than the ambient temperature.
If outlet temperature is less than 50~ Fahrenheit above ambient, the heater core should be replaced with P/N 3091316. Vehicles built between the following VIN breakpoints may be affected by this condition.
Fort Wayne JZ559713 To JZ560949
Oshawa J1583737 To J1584197
Pontiac East JE536922 To JE537614
Parts are currently available from GMSPO.
For vehicles repaired under warranty use:
Labor Op: T7765 Check heater performance (includes measuring air temperature at beater outlet). .5 Hr.
Add: If necessary to replace heater core:
Gas vehicles with A/C .7 Hr.
Diesel vehicles with A/C (incl. charge A/C system) .9 Hr. Gas/Diesel vehicles without
A/C 1.0 Hr.