Heater System - Trouble Shooting Cadillac Escalade GMT400

MODEL IDENTIFICATION

Models are identified by a letter which designates the vehicle series. See GENERAL MOTORS SERIES DESIGNATIONS table.

GENERAL MOTORS SERIES DESIGNATIONS

FUNCTIONAL TEST

1. Idle engine for about 20 minutes until warm or until thermostat opens. Ensure coolant temperature is about 194°F (90°C). Select vent mode. Move temperature lever to coldest temperature setting. Select high blower speed. Air should exit instrument panel outlets and should be about the same temperature as outside air. Air should not exit floor outlets, defrost nozzles, or side window defogger outlets.
2. Select heater mode. Move temperature lever to hottest temperature setting. Most air should exit floor outlets (should be hot), with remaining air exiting defrost and window defogger outlets. Air should not exit instrument panel outlets.
3. Select defrost mode. Most air should exit defrost and defogger outlets, with a low volume of air exiting floor outlets. Move temperature lever to coldest setting. Air temperature should decrease to about the same temperature as outside air.
4. Slowly turn blower motor speed control knob toward OFF position, stopping briefly at each intermediate position to check force of airflow exiting instrument panel center outlets to hear blower speed. Airflow and blower speed should decrease noticeably at each intermediate position.

HEATER OUTPUT TEMPERATURE CHECK

1. Remove radiator cap when engine is sufficiently cool. Select heater (floor) mode, high temperature setting and high blower speed. Idle engine until coolant can be seen flowing in radiator. Install radiator cap.
2. When engine is warm, after about 20 minutes, drive vehicle at 30 MPH (48 km/h). Measure ambient air temperature and floor outlet air temperature using a thermometer. If floor outlet air temperature exceeds minimum specification, heater output temperature is considered sufficient. See «HEATER OUTPUT MINIMUM TEMPERATURE SPECIFICATIONS»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting) table.

HEATER OUTPUT MINIMUM TEMPERATURE SPECIFICATIONS

INSUFFICIENT HEAT DIAGNOSIS

1. Perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) . Go to next step.
2. Common conditions for insufficient heating are as follows: A leak in the cooling system. A low coolant level. A loose or worn drive belt. A leaking or kinked heater hose. A cracked or missing radiator cap seal. Repair condition(s) as necessary and recheck heater operation. See «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) . If heater system operates normally, system is repaired. If heater system does not operate normally, go to next step.
3. Turn ignition switch to ON position. Set mode control to floor/heat position. Set blower speed to HI position. Set temperature control to full hot position. If airflow from floor outlet is high, go to next step. If airflow from floor outlet is not high, go to step 7) .
4. Move blower control through all positions. If blower speed changes, go to next step. If blower speed does not change, go to step 11) .
5. Perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) . If temperatures are as specified, go to next step. If temperatures are not as specified, go to step 12) .
6. Inspect following areas of vehicle for cold air leaks and repair as necessary: At cowl, below windshield. Inside heater case, at door seals. Inside outlet vent ducting. Perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .
7. Perform «FUNCTIONAL TEST»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__functional-test) . If system operates as specified, repairs are complete. If system does not operate as specified, go to next step.
8. Check airflow from instrument panel vent outlets. If airflow from vent outlets is high, go to next step. If airflow from vent outlets is not high, go to step 17) .
9. Move mode control to floor/heat position. A small amount of air should flow from defroster outlets. If airflow from defroster outlets is as specified, go to next step. If airflow from defroster outlets is not as specified, go to step 18) .
10. Remove floor air outlet and check for obstructions. Remove or repair obstructions as necessary. Move blower control through all positions. If blower speed changes, go to step 9) . If blower speed does not change, go to next step.
11. Check following components of blower motor controls and repair as necessary: Blower motor switch Blower motor resistor/relays Blower motor system wiring harness Perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) . If temperatures are as specified, go to step 6) . If temperatures are not as specified, go to next step.
12. Turn temperature control to full hot position. Check temperature valve position. If temperature valve is fully closed, go to next step. If temperature valve is not fully closed, go to step 22) .
13. With temperature control in full hot position, start engine and allow to idle. Check temperature of both inlet and outlet heater hoses. If temperature of air around each heater hose is about the same, 85°F (24°C), go to next step. If temperature of air around each heater hose is not the same, go to step 23) .
14. Remove heater hoses at heater core and check that heater hoses are connected properly. If hoses are properly installed, go to next step. If hoses were not properly installed, go to step 25) .
15. Backflush heater core and service cooling system. Reconnect heater hoses and refill cooling system. Start engine and bring it to normal operating temperature. Recheck temperature of both inlet and outlet heater hoses. If temperature of air around each heater hose is about the same, 85°F (24°C), go to next step. If temperature of air around each heater hose is not the same, go to step 23) .
16. Replace heater core. See appropriate removal and installation procedure in appropriate HEATER SYSTEMS article. After heater core replacement, perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .
17. Set mode control to defrost position. Check airflow from defroster outlet. If there is little or no airflow, go to next step. If airflow is okay, go to step 10) .
18. Move blower control through all positions. If blower speed changes, go to next step. If blower speed does not change, go to step 11) .
19. Check for obstructions at blower motor inlet and at plenum. Repair as necessary. If obstruction was found, go to «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) . If obstruction was not found, go to next step.
20. With blower motor set to HI position, move temperature control from full hot position to full cold position. If change in airflow is present, go to next step. If change in airflow is not present, go to step 26) .
21. Check for restrictions between heater case and instrument panel outlets. Repair as necessary. Go to «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .
22. Re-index cable or actuator. Inspect temperature valve, cables, and linkage adjustment. Repair or replace as necessary. After repairs, perform «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .
23. Check thermostat for proper installation. If thermostat is installed properly, go to step 27) . If thermostat is not installed properly, go to next step.
24. Reinstall thermostat properly and go to step 13) .
25. Reinstall hoses to proper positions and go to step 13) .
26. Inspect the following components and repair as necessary: Temperature valve Control assembly Blower motor wiring harness Go to «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .
27. Replace the thermostat. Go to «HEATER OUTPUT TEMPERATURE CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/heater/#heater-system-trouble-shooting__heater-output-temperature-check) .

See also:
• GENERAL MOTORS SERIES DESIGNATIONS
• HEATER OUTPUT TEMPERATURE CHECK
• FUNCTIONAL TEST