Hummer H1 (2006+). Manual - part 319

11-10 Heating/Ventilation/Air Conditioning (HVAC)

______________________

 Water Valve Does Not Operate

Step Action

Value(s)

Yes

No

1

Actuate the water valve lever by hand, does it 
move freely, and does spring pressure re-open the 
valve when you release it.?

go to step 3.

go to step 2.

2

Replace the tie strap securing the water valve to 
the body. Does the valve move freely now?

Problem is cor-

rected.

Replace the water 

valve.

3

Using a hand vacuum pump J–35555, apply 18” 
Hg to the water valve vacuum motor. Does the 
valve close and hold vacuum for at least 1 minute.

18” Hg

go to step 4.

Replace the water 

valve.

4

Release the vacuum on the water valve, does the 
valve return to the open position?

go to step 5.

Replace the water 

valve.

5

Attach J–35555 to the vacuum supply line for the 
water valve. Turn the ignition key to the on posi-
tion. Rotate the temperature control dial to the 
cold position. Is sufficient vacuum present?

18” Hg

go to step 6.

go to step7.

6

With J–35555 still attached to water valve vac-

uum supply line, rotate the temperature control 
dial to the hot position. Does atmosphere vent in?

0” Hg

System is working 

correctly.

go to step 8.

7

Check for kinks, breaks and blockages in the vac-
uum harness between the water valve and the 
HVAC control head. Are any found?

Repair or replace 

the vacuum har-

ness as necessary.

go to step 9.

8

With J–35555 still attached to the water valve 
vacuum supply line, disconnect the HVAC control 
head 2 hose blk/wht connector. Does atmosphere 
vent in?

0” Hg

Replace the con-

trol head.

Remove the 

blockage in the 

white vacuum 

line to the water 

valve.

9

Disconnect the 2 hose blk/wht connector at the 
HVAC control head. Install J–35555 onto the blk 
hose. Turn the ignition key to the on position. Is 
sufficient vacuum present?

18” Hg

Replace the con-

trol head.

go to step 10.

10

Locate vacuum connection on rear of vacuum 
pump. Install J–35555 onto connection and start 
and idle engine. Is sufficient vacuum present?

18” Hg

Locate and repair 

the blockage/

breakage in vac-

uum harness 

between the vac-

uum pump and the 

HVAC control 

head.

Replace the vac-

uum pump.

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 Heating/Ventilation/Air Conditioning (HVAC)  11-11

Heater Diagnosis

Condition

Possible Cause

Correction

Inadequate or No Heat

1.

Heat control knob not set in heat mode or 
engine not warmed up.

1.

Advise owner/driver.

2.

Low engine coolant level.

2.

Add coolant as needed and check for leaks.

3.

Air the in coolant system. Usually occurs 
after coolant drain and refill.

3.

Bleed air from the cooling system.

4.

Thermostat faulty.

4.

Replace thermostat(s) if stuck closed or
remains open continuously.

5.

Kinked or collapsed radiator hose or heater 
hose.

5.

Replace the hose.

6.

Water pump failure.

6.

Replace the pump.

7.

Heater core plugged or leaking.

8.

Replace the core.

9.

Blower motor fault.

10. Check circuit fuse and wiring. Replace the 

motor if at fault.

11. Outside air leaking into the heater core 

section of the plenum.

12. Seal the plenum or realign as needed.

13. Water control valve or vacuum motor fault.

14. Replace the valve if stuck closed or par-

tially open. Replace motor if open or 
shorted.

15. Blend air door stuck or misadjusted.

16. Repair as needed.

Inadequate Defrost

1.

Duct restricted or connecting hose is loose.

1.

Repair as needed.

2.

Defroster nozzle misaligned or damaged 
(bent, cracked, partially closed).

2.

Repair as needed.

3.

Insufficient heat.

3.

Check for low coolant level, coolant leaks,
air in the system, faulty thermostat or
water valve, collapsed hose, plugged
heater core, binding air door in main unit.

4.

Blower motor fault.

4.

Check circuit fuse and wiring. Replace the
motor if open or shorted.

NOTE: Improperly adjusted or binding mode door linkage can also cause low, poor or no airflow to any location. 

11-12 Heating/Ventilation/Air Conditioning (HVAC)

______________________

Air Flow Diagnosis

Condition

Possible Cause

Correction

No Air Flow from Outlets

1.

Blower motor fuse blown.

1.

Replace the fuse.

2.

Blower motor harness damage (short, 
open, loose connection).

2.

Check the harness continuity with an
ohmmeter and repair as needed.

3.

Blower motor fault.

3.

Run a 12V jumper directly to the motor.
The motor should run at high speed. If the
motor fails to run, replace it. If the motor
runs, check the resistor.

4.

Blower motor resistor fault.

4.

Replace the resistor if the motor runs when
the resistor is bypassed or if the blower
runs at high speed setting but will not run
at one or all of the lower settings.

Air Flows from Incorrect 
Outlets

1.

Actuator motor or linkage fault.

1.

Remove the passenger side trim to expose 
both the actuator motors and observe the 
linkage operation. Adjust the linkage if 
required. Replace the motor and/or linkage 
if inoperative.

Low-Weak Air Flow from 
Outlets

1.

Restriction in air ducts.

1.

 Repair as needed.

2.

Restriction in intake hose into main unit.

2.

 Repair as needed.

3.

Blower motor fault.

3.

Replace the motor or the resistor if either
is inoperative.

4.

Misadjusted or binding mode door linkage. 

4.

 Adjust as necessary. 

 A/C System Diagnosis 

Condition

Possible Cause

Correction

Water on the Passenger 
Side Floor

1.

Evaporator drain hose plugged or installed 
incorrectly.

1.

Open the hose with utility knife or trim end 
off hose. Make sure routing of the hose is to 
the outside of the passenger compartment.

2.

Coolant leak from the heater core.

2.

Replace  the  core  if  leaking.  Replace
clamps or hoses if leaking at the heater
core connections.

3.

Road splash entering the compartment 
through the evaporator/heater core open-
ing, or through the intake air inlet area.

3.

Water test and seal off as needed.

4.

Water leaking into the passenger compartment.

4.

Water test and correct the leaks.

Musty Smell

1.

Water leaking into the passenger compartment.

1.

Water test and correct the leaks.

2.

Evaporator drain partially or fully plugged.

2.

Open or trim off the drain hose with a utility
knife. Correct the routing if necessary.

3.

Mold-Mildew development on the evapora-
tor surface, coils, fins.

3.

Clean the evaporator with a mild disinfectant
soap or replace the evaporator as necessary.

_____________________

 Heating/Ventilation/Air Conditioning (HVAC)  11-13

A/C Pressure Test Diagnosis 

Condition

Possible Cause

Correction

Low Side High
High Side High
(Discharge Air Warm - 
Discharge Line Warm to 
Hot)

1.

Condenser fins obstructed or distorted.

1.

Clear the obstruction with water spray and 
compressed air. Straighten distorted fins 
with tool J–36847 or equivalent.

2.

System overcharged.

2.

Recover excess charge with A/C service
cart J–39500-A.

3.

Air in the system.

3.

Evacuate and recharge the system.

4.

Expansion valve failed.

4.

Replace the valve.

5.

Condenser 

restricted.

5.

Replace the condenser. Evacuate and
recharge the system.

6.

Compressor 

drive 

belt 

slipping.

6.

Replace the belt or belt tensioner as
needed.

Low Side High
High Side High
(Discharge Air Slightly 
Cool - Discharge Line 
Cool)

1.

Air and moisture in the system.

1.

Discharge the system. Replace the 
receiver/dryer and evacuate - recharge the 
system.

2.

Leak at A/C line of 1/2 ounce or less.

2.

Locate  with  J–41995  leak  detector.
Recharge the system and verify proper
operation.

Low Side Low
High Side Low

1.

System low on refrigerant.

1.

Add refrigerant and leak test the system. 
Correct the leak source and recharge as 
needed.
NOTE: If leak was large, check the com-
pressor oil level also and correct as 
needed.

2.

Expansion valve failed.

3.

Replace the valve, then evacuate and 
recharge the system.

Low Side High
High Side Low

1.

Internal leak in compressor

1.

Replace the compressor and evacuate - 
recharge the system.

2.

Expansion valve failure.

2.

Discharge the system. Replace the valve
and recharge the system.

3.

Drive belt slip.

3.

Replace the belt.

Low Side Low
High Side High

1.

Expansion valve failed.

1.

Discharge the system. Replace the valve 
and recharge.

2.

A/C hose constricted, plugged.

2.

Check the hose for kinks. Replace the hose
if plugged and evacuate - recharge the
system.

3.

Receiver/Dryer restricted or has failed.

3.

Evacuate the system. Replace the receiver/
dryer and recharge the system.

4.

Condenser 

problem 

(blocked, 

damaged).

4.

Evacuate the system. Replace the
condenser and recharge the system.