Heater ,defrost, relay

those trucks have a relay that operates the flap that closes the floor heater to operate the defrost the switch is inside the dash by the heater box you will have to check to make sure the wires to the flap are still getting power if not locate the owners manual or a service manual to find the fuse that operates that relay

It can be issue with faulty motor or its faulty fan control relay.
Bother are to be inspected.Test volt at fan relay and fan motor.-------------
For more help,i suggest you to go through the troubleshooting links mentioned below:-----Click the link below:------

How to replace Cooling Fan on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-cooling-fan-on-acura-car.html
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OBD Code P1490 low speed fan relay ckt open-short
http://schematicsdiagram.blogspot.com/2012/11/obd-code-p1490-low-speed-fan-relay-ckt.html
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Engine cooling components working?

http://repairhelpcenter.blogspot.com/2011/11/engine-cooling-components-working.html

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How does Vehicles Engine cooling system works?

http://repairhelpcenter.blogspot.com/2011/11/how-does-vehicles-engine-cooling-system.html

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Hyundai Sonata cooling fan not working

http://schematicsdiagram.blogspot.in/2012/02/hyundai-sonata-cooling-fan-not-working.html

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Fuel pump relay and cooling fan relay troubleshooting on 1997 ford thunderbird?

http://repairhelpcenter.blogspot.com/2011/10/fuel-pump-relay-and-cooling-fan-relay.html
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Fan belt routing diagram for 2004 Volkswagen Jetta?

http://carbeltrouting.blogspot.com/2011/12/fan-belt-routing-diagram-for-2004.html
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Timing belt, drive belt, serpentine belt, accessory belt, fan belt, engine belt routing diagrams for all types of car models?

http://carbeltrouting.blogspot.in/2012/02/timing-beltdrive-beltserpentine.html
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A/C, heater, defroster fan, not working?

http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html
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Blower fan not running on Isuzu trooper?

http://technoanswers.blogspot.in/2012/02/blower-fan-not-running-on-isuzu-trooper.html
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How to replace blower motor fan assembly on 2000 GMC Yukon?

http://repairhelpcenter.blogspot.com/2012/01/how-to-replace-blower-motor-fan.html
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Heater AC or defroster fan not working on KIA?

http://technoanswers.blogspot.in/2012/02/heater-ac-or-defroster-fan-not-working.html
------------These will help.Thanks.

It can be issue with relay or wiring of the fan causing the problem.
Check the help links.Click the link below:---
A/C, heater, defroster fan, not working? http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html

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Heater AC or defroster fan not working on KIA? http://technoanswers.blogspot.in/2012/02/heater-ac-or-defroster-fan-not-working.html

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Where is A/C CONDENSER FAN MOTOR RELAY Located? http://repairhelpcenter.blogspot.com/2011/11/where-is-ac-condenser-fan-motor-relay.html

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How to Remove Fan Clutch ?

http://technoanswers.blogspot.in/2012/04/how-to-remove-fan-clutch-on-2005-gmc.html

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This will help.
Thanks.

For this 1998 chevy cavaleir , the heater blower relay is located in the engine compartment inside the fuse/relay compartment, this box is located on the driverside near fender, i will enclose a picture of its location and also the location of each relay and fuse, you will see the heater relay. good day. hope this helps you.

If the blower isn't working check the fuse/circuit breaker, and relay if one is used. If the blower is working, and if in the defrost mode warm air is produced then it is likely a problem with a vacuum actuator that diverts airflow in the duct system. Some vehicles have a valve that controls hot engine coolant flow to the heater core, if your vehicle has one it will be located where the heater hoses pass through the firewall check to make sure it is functioning correctly.

Please rate this solution.

Could be faulting acutar motor for the hot air door. (1) Heater Core Cover (2) Heater Core (3) A/C Defroster Seal (4) Upper HVAC Module Case (5) Dash Seal (6) A/C Valve (7) Heater/Defroster Valve (8) Temperature Valve (9) A/C Valve Lever (10) Mode Valve Actuator (11) Heater/Defroster Valve Lever (12) Mode Valve Cam (13) Lower HVAC Module Case (14) Rear Heater Duct Seal (15) Temperature Valve Actuator Screw (16) Temperature Valve Actuator (17) HVAC Module Wiring Harness (18) Blower Motor Resistor/Relay Assembly (19) Blower Motor Acoustic Insulator (20) Blower Motor (21) Blower Motor Fan (22) Passenger Compartment Air Filter Access Door (23) Dash Seal (24) Evaporator Block Seal (25) Evaporator Core (26) Passenger Compartment Air Filters (27) Air Inlet Valve (28) Air Inlet Housing (29) Air Inlet Housing Seal (30) Air Inlet Actuator (31) Heater Core Pipe Seal

Heater Core REMOVAL & INSTALLATION For the removal of the heater core, which is located inside the heater-A/C unit assembly, first remove the heater-A/C unit assembly from the vehicle as described later in this section. Once the unit has been removed, use the following procedure to extract the heater core:

1. Place the heater-A/C unit on a suitable work surface.
2. Locate and remove one retaining nut from the blend-air door pivot shaft.
3. To remove the top cover from the heater-A/C case, the crank arm must be removed.
4. Disconnect the vacuum lines from the defroster and panel mode vacuum actuators and position them out of the way.
5. Remove the 3 heater-A/C unit cover attaching screws, fastened upward at the defroster outlet chamber.
6. Remove the 2 heater-A/C unit cover attaching screws, fastened upward at the air inlet plenum.
7. Remove the 11 heater-A/C unit cover attaching screws, fastened downward into the housing. Then lift the cover from the heater-A/C unit.
8. Remove the old heater core from the case. To install:
   
9. Install the new heater core into the heater-A/C unit case in the same position as the old one.
10. Place the cover onto the case and secure in place with the 11 retaining screws.
11. Install the 2 heater-A/C unit cover attaching screws in the air inlet plenum.
12. Install the 3 heater-A/C unit cover attaching screws in the defroster outlet chamber.
13. Attach the vacuum lines from the defroster and panel mode vacuum actuators to the heater-A/C unit case.
14. Install the crank arm and the retaining nut on the blend-air door pivot shaft.
15. Install the heater-A/C unit assembly into the vehicle.

check blower motor.. give it a tap when you start the vehicle and turn on the heat.. if it come on then you would have to replace the blower motor..if it does not check for fuse..

on the right side of steering colum there is a plug. there is a wire that gets warm and loses connection. check by moving plug. my heater and ac would not work and caused the vacume swith to stay open.

There are 3 fuses that control the rear defogger, and 1 relay

The fuses are: 10 amp HEATER, 10 amp MIRROR-HEATER; under the dash
The 30 amp DEF fuse is in the fuse box under the hood
The relay is the DEFOGGER relay, which is on the back side of the fuse panel under the dash

Also, check for a loose wire on the defroster grid (on the back glass), this is the most common problem.