Mechanics

HOW TO FIX THE MIXING DOORS ON

1999 Cadillac STS • 170,000 miles

I have no heat on the passenger side and need to know how to fix the mixing doors
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Old-sarge
January 3, 2012.



HVAC SYSTEM - MANUAL - TROUBLESHOOTING -1999 Cadillac Seville STS
Page 1 of 1
HEATER OUTPUT TEMPERATURE CHECK

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Question: Heat only on right side
Tech1
1.
Select heater (floor) mode, high temperature setting and high blower speed. Idle engine for about 20 minutes or until engine reaches normal operating temperature.
Drive vehicle at 30 MPH (48 KM/H). Measure ambient air temperature and floor outlet air temperature. If floor outlet air temperature exceeds minimum specification, heater output
temperature is considered sufficient. See HEATER OUTPUT TEMPERATURE MINIMUM SPECIFICATIONS table.
2.
HEATER OUTPUT TEMPERATURE MINIMUM SPECIFICATIONS
Ambient Air Temp. °F (°C) 0 (-18)
25 (-4) 50 (10)
75 (24)
Floor Outlet Air Temp. °F (°C) 110 (43)
125 (50) 140 (60)
150 (66)

HVAC SYSTEM - MANUAL - TROUBLESHOOTING -1999 Cadillac Seville STS
Page 1 of 1
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 bi-level mode. Move temperature lever to coldest
temperature setting. Select high blower speed. Air should exit all outlets and should be about the same temperature as outside air.
2. Select vent mode. Air should exit vent outlets and should be about the same temperature as outside air. Air should not exit floor, defrost, or window defogger outlets.
3. Select heater (floor) mode. Most air should exit floor outlets, with remaining air exiting defrost and window defogger outlets. Air should not exit vent outlets. Air should be about the same
temperature as outside air.
4. Select blend (floor-defrost) mode. An equal volume of air should exit defrost and floor outlets, with some air exiting side window defogger outlets.
5. Select defrost mode. Most air should exit defrost outlets, with a low volume of air exiting floor outlets.
6. Select bi-level mode. Move temperature lever to maximum hot setting. Air should exit vent outlets and its temperature should rapidly increase to about 131°F (55°C) or greater. For more precise
heater output temperature check, see HEATER OUTPUT TEMPERATURE CHECK. Defrost nozzle airflow volume should diminish and floor outlet airflow volume may increase slightly.
Move temperature lever to maximum cold setting. Air temperature should decrease to about the same temperature as outside air.
Slowly turn blower motor speed control **** toward OFF position, stopping briefly at each intermediate position to check force of airflow exiting instrument panel center outlets to hear
blower noise. Airflow and blower noise should decrease noticeably at each intermediate position.

HVAC SYSTEM - MANUAL - TROUBLESHOOTING -1999 Cadillac Seville STS
Page 1 of 2
INSUFFICIENT HEATING

Insufficient heating may be caused by any of the following conditions: ? Low coolant level.
? Loose or worn coolant pump drive belt.
? Partially or fully clogged heater core or heater hose. ? Obstruction to air circulation.
? An air leak into passenger compartment.
1.
Inspect cooling system and components for any of the conditions listed above. Repair as necessary. If no system faults are detected at this time, go to next step.
2. Place heater controls to heat mode. Place blower speed control to highest setting. Place temperature control to full warm position. Start engine and allow to idle. Inspect floor air outlet. If
there is a high airflow, go to next step. If there is not a high airflow, go to step 15.
Inspect blower speed for airflow change with changes in blower speed switch. If airflow changes in relation to blower switch change, system is okay at this time. If airflow does not change with
changes in blower speed switch position, go to next step.
4. Inspect blower speed switch and/or blower motor resistor. Repair or replace as necessary. Check for heater output. See HEATER OUTPUT TEMPERATURE CHECK. If heater output check
is okay, go to next step. If heater output is not correct, go to step 6.
Inspect vehicle for air leaks at the cowl, heater case, and vents. Inspect under the seat for obstructions.
Turn ignition on. Place blower on low speed setting. Place temperature control to mid-position. Rapidly move temperature control to full hot position. Listen for slam of temperature door. If slam
of door is not heard, go to next step. If temperature door slam is heard, go to step 8.
Inspect temperature control cable for correct adjustment. See appropriate ADJUSTMENTS article. Adjust, repair or replace as necessary.
Place temperature to full warm position. Start vehicle. Check temperature of heater inlet and outlet hoses by feel. If inlet hose is warmer than outlet hose, go to step 12. If inlet hose is not warmer
than outlet hose, go to next step.
Back flush heater core. Drain and refill cooling system. Retest heater system operation. See HEATER OUTPUT TEMPERATURE CHECK.
Repeat heater test. See HEATER OUTPUT TEMPERATURE
exist, go to next step. Replace heater core.
Check thermostat for proper installation and seating. If thermostat is properly installed, go to step 14.
Replace thermostat.
Remove, inspect, and install thermostat properly. Perform functional check. See FUNCTIONAL CHECK
Inspect airflow from defroster and vent outlets. If airflow from these outlets is good, go to next step. If airflow from these outlets is poor, go to step 18.
Inspect vacuum system of A/C-heater system. Repair as necessary.
3.
5.
6.
7.
8.
9.
CHECK
10.
. If symptoms still
11. 12.
13. 14.
15. 16.
.
17.

1/2/2012
HVAC SYSTEM - MANUAL - TROUBLESHOOTING -1999 Cadillac Seville STS
Page 2 of 2
18.
Place mode control to defrost position. If airflow is coming from defroster outlets, go to next step. If airflow is not coming from defroster outlets, go to step 20.
Inspect floor air outlet for obstructions.
Check for changes in airflow velocity, in relation to changes in blower speed setting.
Inspect blower inlet for obstructions. Repair as necessary. If no obstructions exist, go to next step. Place blower on high speed setting. Move temperature control from full warm to full cold
position, while listening for change in airflow. If there is a change in speed of airflow, go to next step. If there is no change in airflow speed, go to step 24.
Inspect for obstruction between blower and system outlets. Repair as necessary.
Inspect temperature control valve, temperature control cable, and other temperature control components. Repair as necessary.
19. 20. 21.
22.
23. 24.

Rivermikerat
Jan 3, 2012.


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