Question about 1991 GMC Sierra

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1991 sierra air cond. light is flashing on an off

Ac light on heater controls is flashing on and off

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6 Suggested Answers

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Posted on Jan 02, 2017

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matney68
  • 426 Answers

SOURCE: 1991 Sie rra GMC AC control problem

this will happen if the system senses low charge. This doesnt mean that is the problem the low pressure switch or cycling switch on the accumulator/dryer on passenger side firewall will also keep in from coming on. this can be checked by jumping the system there.If you jump it and it comes on and air is cold on both sides of cab this could definately be the problem.

Posted on Jun 29, 2009

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SOURCE: 1991 Sierra GMC AC control problem

The follwing is a cut and paste from a service bulletin:

Bulletin No.: 461202

Date: May, 1994

SUBJECT:
A/C CONTROL HEAD FLASHES OR ERRATIC OPERATION OF A/C CONTROLS (POLISH
TERMINALS)

MODELS:
1988-94 CHEVROLET AND GMC TRUCK C/K MODELS
1990-94 CHEVROLET AND GMC TRUCK TOPKICK/KODIAK MODELS WITH C60 OR C69 AIR
CONDITIONING

CONDITION:

A/C Control Head flashes, performs erratically or malfunctions.

CAUSE:

Light surface corrosion on the Control Head terminals.

CORRECTION:

Remove the A/C Control Head and while holding the unit with the terminal
cavity down (toward the floor) so no particles will fall inside on the
circuit boards, polish the terminals on both sides of the cavity with a lead
pencil pink eraser. Do not use an ink eraser or other abrasive such as a
small wire brush or sandpaper, etc. Doing so will remove the terminal
coating and degrade the contact surface.

Performing this procedure, in many cases, will make replacing the Control
Head unnecessary. Using this procedure in conjunction with the A/C circuit
diagnosis found in the Electrical Diagnosis Manual and especially before
replacing a Control Head for any reason is recommended.

After polishing the Control Head terminals, but before reconnecting, check
for proper terminal contact as described in the applicable electrical
diagnosis manual. If contact is good, apply dielectric grease (P/N 12345579)
to the harness connector terminals. Please do not apply grease to the
Control Head.

Posted on Jun 30, 2009

  • 6 Answers

SOURCE: 2000 gmc sierra 1500 5.3 v8. a/c heater control problem

your heat/cool and vent selection options are controlled by engine vacuum through small clear tubes attached to the rear of your climate control interface. Other vehicles have small steel pull wires that operate the desired changes. You might try removing the trim and any fasteners affiliated with the interface/console. GENTLY pull outward and look to see if any of these tubes are pulled off or cut/damaged. Did anyone recently install a new stereo in the vehicle? If so, the vacuum tubing and or pull wires that change your outlets could have been damaged when the stereo unit was pushed into place. Hope this helps

Posted on Sep 09, 2009

Testimonial: "Very good information. THANKS!"

  • 1509 Answers

SOURCE: 2004 gmc 1500 sierra heater control stuck on

Defrost is the default position. Is the control a autyomatic temperture control unit? ( you set the temp and select automatic) if it is the system is completely electronic. You push the buttons and the control still says defrost or can you select something else and the control shows it but it just keeps coming out the defrost? If the control changes and the air comes out the defrost anyway and the cheack engine light isn't on, then the problem can be blown fuses or an air door actoater not working. Does the dash emit a clicking sound? if it does with the covers off the bottom of the dash reach around touching the different pieces till you touch the idem that is clicking. this is an acutor motor, or blend door motor. they have gears in them that wear out and break the motors aren't repairable and you just replace the ofending motor. the door that is moves can be stuck. and may have to be freed up with blaster, WD40, or other rust buster till it moves easy. maybe after getting the door to move smoothly you can get the old motor to move the door wiithout having to install a new one.

Posted on Jan 06, 2010

  • 432 Answers

SOURCE: 93 Sierra - Cabin Heater Lights Flashing - Is that a warning?

Well this will tell you that the door that directs the air flow in not moving fully into position.Either the motor that moves the door is not working correctly or there is something obstructing the door.We had mice build a nest in the air ducts and would only do heat any other selection would make the arrow flash until we cleaned it out.Well hope this helped.

Posted on Mar 13, 2010

Testimonial: "Hey thanks! It wasn't mice but the spring had popped out and desengaged the arm from the servo motor, put it back together and she's fixed. Thanks!!!"

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1 Answer

1991 gmc sierra 1500 p/u-can not locate blower motor speed control resistor. I've looked under dash, pulled out glove compartment, looked on firewall, I give up.


If its not near the blower motor, it may be on the hvac box on the firewall in the engine compartment. It depends on if it has ac or not.
They are usually behind the glove box mounted in the side of the heater box.

Sep 26, 2013 | 1991 GMC Sierra

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1999 GMC air cond. AC clutch wont engage. system is charged. relay, fuze,and low pressure switch are replaced.


ac compressor clutch coil open or short. wire cut or open to ac clutch.2 wires one is ground the other power, remove connector ac compressor then probe with test light between the two wire

Aug 05, 2013 | 2003 GMC Sierra 1500

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Does my heater coil work off a vacum system to switch from air cond, to heat


Sounds like it could be a faulty heater control valve.

Feb 01, 2012 | 1998 GMC Sierra

1 Answer

Heater blowing cold air. like air cond. on. i changed thermostat


If the car is otherwise running fine, then the thermostat is almost never an issue. you need to take a look at the heater core and any heater valve stuck in a heater hose, that is where most of those issues are resolved.

Nov 18, 2010 | 1999 GMC Sierra

3 Answers

Air conditioner problem


Sounds like a problem with the censor or a bad pig tail, try unplugging the pig tail and sticking a paper clip in both sides and then turn the ac on, that will tell you which it is

Jun 17, 2010 | 1992 GMC Sierra

3 Answers

1991 Sierra GMC AC control problem


The follwing is a cut and paste from a service bulletin:

Bulletin No.: 461202

Date: May, 1994

SUBJECT:
A/C CONTROL HEAD FLASHES OR ERRATIC OPERATION OF A/C CONTROLS (POLISH
TERMINALS)

MODELS:
1988-94 CHEVROLET AND GMC TRUCK C/K MODELS
1990-94 CHEVROLET AND GMC TRUCK TOPKICK/KODIAK MODELS WITH C60 OR C69 AIR
CONDITIONING

CONDITION:

A/C Control Head flashes, performs erratically or malfunctions.

CAUSE:

Light surface corrosion on the Control Head terminals.

CORRECTION:

Remove the A/C Control Head and while holding the unit with the terminal
cavity down (toward the floor) so no particles will fall inside on the
circuit boards, polish the terminals on both sides of the cavity with a lead
pencil pink eraser. Do not use an ink eraser or other abrasive such as a
small wire brush or sandpaper, etc. Doing so will remove the terminal
coating and degrade the contact surface.

Performing this procedure, in many cases, will make replacing the Control
Head unnecessary. Using this procedure in conjunction with the A/C circuit
diagnosis found in the Electrical Diagnosis Manual and especially before
replacing a Control Head for any reason is recommended.

After polishing the Control Head terminals, but before reconnecting, check
for proper terminal contact as described in the applicable electrical
diagnosis manual. If contact is good, apply dielectric grease (P/N 12345579)
to the harness connector terminals. Please do not apply grease to the
Control Head.

Jun 29, 2009 | 1991 GMC Sierra

1 Answer

1991 Sie rra GMC AC control problem


this will happen if the system senses low charge. This doesnt mean that is the problem the low pressure switch or cycling switch on the accumulator/dryer on passenger side firewall will also keep in from coming on. this can be checked by jumping the system there.If you jump it and it comes on and air is cold on both sides of cab this could definately be the problem.

Jun 29, 2009 | 1991 GMC Sierra

2 Answers

FUSE BOX DETAILS


left to right...
1. empty
2. e flashers
3.horn, brake lights
4.clock, trunk light, inside light, radio
5. rad. cooling fan relay (AC only)
6. right side running lights
7. left side running lights
8. right high beam and indicator
9. left high beam and indicator
10. right low beam
11. left low beam
12. reverse,turn signal and inst panel
13. main and transfer fuel pumps, auxiliary air reg., ox sensor heater
14. license plate and glove box light
15. wipers
16. rear defogger
17. heater blower (no AC)
18. cig lighter
19. rad cooling fan (no AC)
20. Heater blower (AC)
21. rad cooling fan (AC only)
22. empty
23. Ox sensor, idle stabilizer,seat belt warning relay, (Digifant only, control unit, idle boost control, idle boost valve)
24. inst panel lights, heater control lights
25. reading lamps
26. empty
27. empty
28. empty

Hope this helps...;-)

Apr 17, 2009 | 1992 Volkswagen Fox

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