I need a new valve that is air operated and is used for the heat in the vehicle. It is a three-way and is connected to the heater core tubing. What is the correct part name for this plastic valve?

Possibly plugged or inerporable heater core. Possibly heater core valve (this diverts hot air through your heater system) When you flushed the block, was there a lot of contaminant? 95% of the time, cold heat means thermostat. Also there are a lot of really cheap after market thermostats, you can buy one as low as $6.00. That being said, just because a thermo is new doesn't necessarily mean it opens/shuts when it should. You can look on You Tube on how to test one in your kitchen with boiling water,.

So three basic things affect interior heat temps. Thermostat, plugged heater core/.valve, and insufficient coolant or liquid to tranfser heat. If your interior coolant (engine temp) is working normally and your vehicle reaches operating tempature according to the needle, your thermosat is probably not the cause.

My bet is somehow, your heater core is plugged so that their is not enough "flow"

If the heater core (2 heater core tubes at firewall) is hot and the interior is cold, then the blend door is causing your problem. It is controlled by electrical and vacuum components.

Also, note that the heater core tubes have a valve that is replaced with the entire hose.

Also, the heater core, if plugged can be replaced as follows:
Heater Core REMOVAL & INSTALLATION

1. Disable the SIR system, as outlined in this section.
2. Disconnect the negative battery cable.
3. Properly drain the cooling system.
4. Raise and safely support the vehicle.
5. Detach the heater hoses from the heater core.
6. Carefully lower the vehicle.
7. Remove the instrument panel. For details, please refer to the procedure located in Section 10 of this manual.
8. Remove the DERM with the attaching bracket.
9. Detach the heater core cover.
10. Unfasten the heater core mounting clamps, then remove the heater core. Fig. 1: Exploded view of the heater core and related components
    To install:
    
11. Position the heater core, then secure with the mounting clamps.
12. Attach the heater core cover.
13. Install the DERM with the attaching bracket.
14. Install the instrument panel, as outlined in Section 10 of this manual.
15. Raise and safely support the vehicle.
16. Connect the heater hoses to the core.
17. Carefully lower the vehicle.
18. Properly refill the engine cooling system and check for leaks.
19. Enable the SIR system.
20. Connect the negative battery cable, then start the engine and check for proper system operation and/or leaks.

If it's not blowing out hot air, the blend door may be the problem on the 1990 Isuzu Trooper.

Heater Water Control Valve REMOVAL & INSTALLATION On early models the heater control valve was part of the heater core inlet. To replace the control valve, remove the heater core as outlined in this section. Remove the control valve from the heater core, being careful not to damage the core. Use new gaskets when installing new valves. The remainder of the vehicles are not equipped with heater water control valves. They use heater unit doors to regulate the amount of heat entering the vehicle. --- I would check that both tubes running to the heater core are getting hot. If they are, then there is a blend door problem. If both tubes are not getting hot, the heater core is blocked somewhere or the heater control valve, if so equipped, is in need of replacement. Good luck on this repair.

Check your coolant level. If your coolant level is good then look at your heater core. With the engine running touch both heater hoses that go through the firewall in your engine compartment. Both should be hot to the touch. If only one is hot, you have a blockage somewhere. Worst case scenario you'll need a new heater core.

what year? for 2000, there are no control valves. It mixes a/c air with heater core air to blend the right temp.

SECTION 412-02: Heating and Ventilation 2000 Expedition/Navigator Workshop Manual
DESCRIPTION AND OPERATION Heating/Defrosting The heating and defrosting system has the following features:

• Controls the temperature and, during A/C operation, reduces the relative humidity of the air inside the vehicle.
• Delivers heated or cooled air to maintain the vehicle interior temperature and comfort level.
• Controls the A/C blower motor speed.
• Cooling or heating can be adjusted to maintain the desired temperature.
• Uses a reheat method to provide conditioned air to the passenger compartment.
• The blower motor draws outside air through the A/C recirculating air duct, except for MAX A/C cooling, when recirculated air is used.
• All airflow from the blower motor passes through the A/C evaporator core.
• The temperature is then regulated by reheating a portion of the air and blending it with the remaining cool air to the desired temperature.
• The temperature blending is controlled by the temperature blend door, which regulates the amount of air that flows through and around the heater core, where it is then mixed and distributed.

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Removal & Installation
CAUTION When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

1. Disconnect the negative battery cable and drain the cooling system.
   
2. Raise and support the vehicle safely.
   
3. If equipped, remove the rear lateral transaxle strut mount.
   
4. Disconnect the drain tube from the heater case.
   
5. Detach the heater hoses from the heater core.
   
6. Carefully lower the vehicle.
   
7. Remove the right and left sound insulators.
   
8. Unfasten the steering column opening filler. Disconnect the heater outlet deflector (floor air outlet duct).
   

Disconnect the floor air outlet duct

Remove the heater core cover.


Unfasten the retaining bolts, then remove the heater core cover

Detach the heater core retaining straps (clamps), then remove the heater core.


Detach the retaining clamps or straps, then remove the heater core


To install:

1. Install the heater core and retaining straps (clamps).
   
2. Install the heater core cover.
   
3. Reconnect the heater outlet deflector (floor air outlet duct).
   
4. Install the right and left sound insulators. Install the steering column opening filler.
   
5. Raise and support the vehicle safely.
   
6. Connect the heater hoses (use new heater hose clamps if necessary) to the heater core.
   
7. Connect the drain tube to heater case.
   
8. Connect the rear lateral transaxle strut mount, if equipped.
   
9. Lower the vehicle.
   
10. Fill the cooling system and check for leaks. Check heater system for proper operation.
    

the temp blend door may not be rotating from the a/c evaporator to the heater core opening.

Could be the motor on the blend door or the temp control knob.

Do you have manual a/c or electronic temp control?

If it's the a/c door electronic actuator motor, it's on top of the plenum. Have to remove the instrument panel for access.

Hope it's the temp knob on the control head.

top one is the circuit you are looking at

1991-95 Models

1. Disable the air bag system by disconnecting the negative battery cable.
2. Have the system discharged by a qualified professional mechanic using an approved recovery/recycling machine.
3. Drain the cooling system.
4. Remove the steering column cover and left and right side under panel silencers.
5. Remove the center bezel by unclipping it from the instrument panel.
6. Remove the accessory switch carrier and the heater/air conditioning control head.
7. Remove storage bin and lower right instrument panel.
8. Disconnect the blower motor lead under the right side of the instrument panel.
9. Remove the right side 40-way connector wiring bracket.
10. Remove the lower right reinforcement, body computer bracket and mid-to-lower reinforcement as an assembly.
11. Disconnect the vacuum lines at the brake booster and water valve.
12. Clamp off the heater hoses near the heater core and remove the hoses from the core tubes. Plug the hose ends and the core tubes to prevent spillage of coolant.
13. If equipped with air conditioning, remove the H-valve and condensation tube.
14. Disconnect the temperature control cable and vacuum harness at the connection at the top of the unit.
15. Remove the retaining nuts from the package mounting studs at the firewall. Disconnect the hanger strap from the package and rotate it aside.

To install:

1. Remove the temperature control door from the unit and clean the unit out with solvent. Lubricate the lower pivot rod and its well and install. Wrap the heater core and/or evaporator with foam tape and place in position. Secure with the screws.
2. Assemble the unit, making sure all vacuum tubes are properly routed.
3. Install the assembly to the vehicle and connect the vacuum harness. Install the nuts to the firewall and install the condensation tube. Fold the carpeting back into position.
4. Connect the hanger strap from the package and rotate it aside. Install the 2 brackets supporting the lower edge of the heater housing. Connect the blower motor wiring, resistor wiring and the temperature control cable.
5. Install the retaining screws from the right side to the steering column. Install the instrument panel trim covering and reinforcement.
6. Assemble the unit, making sure all vacuum tubes are properly routed.
7. Install the assembly to the vehicle and connect the vacuum harness. Install the nuts to the firewall and install the condensation tube. Fold the carpeting back into position.
8. Connect the hanger strap from the package and rotate it aside. Connect the blower motor wiring and temperature control cable.
9. Install the lower right reinforcement, body computer bracket and mid-to-lower reinforcement as an assembly.
10. Install the right side 40-way connector wiring bracket.
11. Install the lower right instrument panel and storage bin.
12. Install the heater/air conditioning control head and accessory switch carrier.
13. Install the center bezel to the instrument panel.
14. Install the under panel silencers and steering column cover.
15. Install the vacuum lines at the brake booster and water valve.
16. Connect the heater hoses to the core tubes.
17. Using new gaskets, install the H-valve and connect the refrigerant lines. Install the condensation tube.
18. Have the system evacuated and recharged by a qualified professional mechanic, utilizing the proper equipment. Add 2 fl. oz. (59 ml) of refrigerant oil during the recharge. Fill the cooling system.
19. Perform the Air Bag System Check procedures outlined in this section before connecting the negative battery cable.
20. Connect the negative battery cable and check the entire climate control system for proper operation and leaks.

REMOVAL

WARNING:

• ON VEHICLES EQUIPPED WITH AIRBAGS, DISABLE THE AIRBAG SYSTEM BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE, THEN WAIT TWO MINUTES FOR THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE BEFORE PERFORMING FURTHER DIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN AN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.
• REVIEW THE WARNINGS AND CAUTIONS IN THE FRONT OF THIS SECTION BEFORE PERFORMING THE FOLLOWING OPERATION. See: Heating and Air Conditioning\Service Precautions

1. Remove the HVAC housing from the vehicle. See: Heating and Air Conditioning\Housing Assembly HVAC\Service and Repair
2. Remove the foam gasket surrounding the core tubes. NOTE: Notice the orientation of the irregularly shaped gasket on the tubes. The gasket must be placed correctly to ensure proper sealing against the body during reinstallation
   1. Remove the screws and retainers that secure the heater core and tubes to the HVAC housing.
   2. Remove the mode door actuator if necessary for clearance to remove the core.
      1. Lift the heater core straight up and out of the HVAC housing.
      2. When replacing individual tubes, loosen and remove the round tube-to-core clamp, and pull tube from core.
      INSTALLATION
      
      WARNING: REVIEW THE WARNINGS AND CAUTIONS IN THE FRONT OF THIS SECTION BEFORE PERFORMING THE FOLLOWING OPERATION. See: Heating and Air Conditioning\Service Precautions
      
      Any kinks or sharp bends in the refrigerant plumbing will reduce the capacity of the entire air conditioning system. Kinks and sharp bends reduce the flow of refrigerant in the system. A good rule for the flexible hose refrigerant lines is to keep the radius of all bends at least ten times the diameter of the hose. In addition, the flexible hose refrigerant lines should be routed so they are at least 80 millimeters (3 inches) from the exhaust manifold.
      
      High pressures are produced in the refrigerant system when the air conditioning compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.
      
      
      
      1. When installing individual tubes, insert tube into core ensuring that tube O-ring is seated in core and not pinched. Hold tube in seated position while installing the round tube-to-core clamp. NOTE: The round tube-to-heater-core clamp should be left loose enough to turn the tube in the core. Position the core in the housing, and then tighten the tube-to-heater-core clamp after orienting the tubes to the molded HVAC housing.
      2. Lower the heater core into the HVAC housing.
      3. Install the mode door actuator, if removed from housing for core removal.
      4. Position the retainers over the heater core tubes. Install and tighten the screws that secure the heater core and retainers to the HVAC housing. Tighten the screws to 2.2 Nm (20 in. lbs.) . NOTE: The grounding strap is to be attached to the lower heater core tube retainer.
      5. Reinstall the HVAC housing to the vehicle. See: Heating and Air Conditioning\Housing Assembly HVAC\Service and Repair

1. Position the HVAC housing to the dash panel. Be certain that the evaporator condensate drain tube and the housing mounting studs are inserted into their correct mounting holes.
2. Install the HVAC housing mounting nuts to the studs on the passenger compartment side of the dash panel. Tighten the nuts to 4.5 Nm (40 in. lbs.) .
3. Connect the HVAC housing wire harness connectors.
4. Reinstall the rear floor heat ducts to the center floor heat duct outlets.
5. Install and tighten the nuts onto the HVAC housing mounting studs on the engine compartment side of the dash panel. Tighten the nuts to 7 Nm (60 in. lbs.) .
6. Reinstall the PCM to the passenger side dash panel in the engine compartment. See: Powertrain Management\Computers and Control Systems\Engine Control Module\Service and Repair
7. Reinstall the coolant reserve/overflow bottle to the passenger side inner fender shield. See: Engine, Cooling and Exhaust\Cooling System\Coolant Reservoir
8. If the vehicle is equipped with the manual temperature control system, connect the HVAC system vacuum supply line connector to the tee fitting near the heater core tubes.
9. Unclamp/unplug the heater core hoses and tubes. Connect the heater hoses to the heater core tubes and fill the engine cooling system. See: Engine, Cooling and Exhaust\Cooling System\Service and Repair
10. Unplug or remove the tape from the suction line and the evaporator outlet tube fittings. Connect the suction line to the evaporator outlet tube. Tighten retaining nut to 28 Nm (250 in. lbs.) .
11. Unplug or remove the tape from the liquid line and the evaporator inlet tube fittings. Connect the liquid line to the evaporator inlet tube. Tighten retaining nut to 28 Nm (250 in. lbs.) .
12. Evacuate the refrigerant system. See: Refrigerant\Service and Repair
13. Charge the refrigerant system. See: Refrigerant\Service and Repair
14. Install the instrument panel in the vehicle. Refer to: Body and Frame, Interior Trim, Dashboard/Instrument Panel, Service and Repair, Instrument Panel Service Procedures, Instrument Panel Assembly Replacement, See: Body and Frame\Interior Moulding / Trim\Dashboard / Instrument Panel\Service and Repair\Procedures\Instrument Panel Assembly Replacement
15. Connect the battery negative cable.
16. Start the engine and check for proper operation of the heating and air conditioning systems.
    

The heater-A/C housing assembly must be removed from the vehicle and the two halves of the housing separated for service access of the heater core, evaporator coil, blend-air door, and each of the various mode control doors.

WARNING: On vehicles equipped with airbags, refer to Airbag Systems Safety Information and Procedures. Before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Failure to take the proper precautions could result in accidental airbag deployment and possible personal injury. See: Restraint Systems\Air Bag Systems\Service Precautions

REMOVAL

1. Disconnect and isolate the battery negative cable.
2. Remove the instrument panel from the vehicle. Refer to: Body and Frame, Interior Trim, Dashboard / Instrument Panel, Service and Repair, Instrument Panel Service Procedures, Instrument Panel Assembly Replacement, See: Body and Frame\Interior Moulding / Trim\Dashboard / Instrument Panel\Service and Repair\Instrument Panel Assembly
3. If the vehicle is not equipped with air conditioning, go to Step 6. If the vehicle is equipped with air conditioning, recover the refrigerant from the refrigerant system. Refer to: Heating and Air Conditioning, Service and Repair, Procedures, Refrigerant System Recovery, See: Service and Repair\Refrigerant System Recovery
4. Disconnect the liquid line refrigerant line fitting from the evaporator inlet tube.

• Install plugs in, or tape over all of the opened refrigerant line fittings.

1. Disconnect the accumulator inlet tube refrigerant line fitting from the evaporator outlet tube. See Refrigerant Line Coupler for the procedures.

• Install plugs in, or tape over all of the opened refrigerant line fittings.

1. Drain the engine cooling system.
2. Disconnect the heater hoses from the heater core tubes. Install plugs in, or tape over the opened heater core tubes.
3. Unplug the heater-A/C system vacuum supply line connector from the tee fitting near the heater core tubes.
4. Unplug the heater-A/C unit wire harness connector, which is fastened to the heater-A/C housing next to the blower motor relay.
   1. Remove the five nuts from the heater-A/C housing mounting studs on the engine compartment side of the dash panel. Remove or reposition the evaporation canister for additional access, if required.
   2. Pull the heater-A/C housing rearward far enough for the mounting studs and the evaporator condensate drain tube to clear the dash panel holes.
   3. Remove the heater-A/C housing from the vehicle.
   INSTALLATION
   
   1. Position the heater-A/C housing to the dash panel. Be certain that the evaporator condensate drain tube and the housing mounting studs are inserted into their correct mounting holes.
   2. Install and tighten the five nuts onto the heater-A/C housing mounting studs on the engine compartment side of the dash panel. Tighten the nuts to 6.2 Nm (55 in. lbs.) .
   3. If the evaporation canister was repositioned during the removal procedure, reinstall it to its proper position.
   4. Connect the Heater-A/C system vacuum supply line connector to the tee fitting near the heater core tubes.
   5. Unplug or remove the tape from the heater core tubes. Connect the heater hoses to the heater core tubes and fill the engine cooling system.
   6. If the vehicle is not equipped with air conditioning, go to Step 10. If the vehicle is equipped with air conditioning, unplug or remove the tape from the accumulator inlet tube and the evaporator outlet tube fittings. Connect the accumulator inlet tube coupler to the evaporator outlet tube.
   7. Unplug or remove the tape from the liquid line and the evaporator inlet tube fittings. Connect the liquid line coupler to the evaporator inlet tube.
   8. Evacuate the refrigerant system. Refer to: Heating and Air Conditioning, Service and Repair, Procedures, Refrigerant System Evacuate, See: Service and Repair\Refrigerant System Evacuate
   9. Charge the refrigerant system. Refer to: Heating and Air Conditioning, Service and Repair, Procedures, Refrigerant System Charge, See: Service and Repair\Refrigerant System Charge
   10. Install the instrument panel in the vehicle. Refer to: Body and Frame, Interior Trim, Dashboard / Instrument Panel, Service and Repair, Instrument Panel Service Procedures, Instrument Panel Assembly Replacement, See: Body and Frame\Interior Moulding / Trim\Dashboard / Instrument Panel\Service and Repair\Instrument Panel Assembly
   11. Connect the battery negative cable.
   12. Start the engine and check for proper operation of the heating and air conditioning systems.

REMOVAL AND INSTALLATION

WARNING: On vehicles equipped with airbags, refer to Airbag Systems Safety Information and Procedures. Before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Failure to take the proper precautions could result in accidental airbag deployment and possible personal injury. See: Restraint Systems\Air Bag Systems\Service Precautions

1. Remove and disassemble the heater-A/C housing. Refer to: Heating and Air Conditioning, Housing Assembly HVAC, Service and Repair, See: Heating and Air Conditioning\Housing Assembly HVAC\Service and Repair
2. Lift the heater core out of the lower half of the heater-A/C housing.
3. Reverse the removal procedures to install. Be certain that the heater core foam insulator is reinstalled