I have a '92 gmc k1500. On the heater control, the indicator for cold......hot flashes. I am aware of the a/c fashing light indicating low refrigerant. That is not the problem. When the a/c button is pushed, the compressor will run, it is not felt in the cab because the heat is on at the same time. Is the control assembly bad or is it something else? Could it be mechanical?

SOURCE: 1990 gmc 1500 heater motor does not turn on

The fan switch itself is a possibility, but there is also a resistor pack behind the glove compartment. Hi speed doesn't use the resistors, though, so if it doesn't run on hi, it narrows it down to the switch, the motor, the motor ground, or the blower relay, or any of the associated wire connectors.

dave smith

• 94 Answers
• Posted on Feb 25, 2009

SOURCE: heating problem

 more likely a bad blower motor relay.

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.

SOURCE: 96 gmc jimmy a/c

50psi on the low side is a little high. Sounds like the system is overcharged by about 10-15psi. Overcharging a system will cause a lack of performance just as much as undercharging with one exception, overcharging can damage the compressor. The compressor will engage with as little as 20psi although there's no 1 benchmark for all engines, 40-45psi is considered a full charge. Hope this answers your question.
Greg

Greg Bernett

• 2993 Answers
• Posted on Oct 02, 2009

SOURCE: how to replace the blower motor fan assembly in a

Blower Motor Removal & Installation Delphi
Blower Motor Replacement (Delphi)


To Remove:

1. Remove the instrument panel sound insulator panel (if equipped).
2. Disconnect the electrical connector from the blower motor.
3. Remove the blower motor insulating cover screws.
4. Remove the blower motor insulating cover.
5. Pull the retaining tab down and rotate blower motor counterclockwise to remove.

1. Position the blower motor and turn assembly clockwise until tab locks in place.
2. Install the blower motor insulating cover.
3. Connect the electrical connector to the blower motor.
4. Install the instrument panel sound insulator panel (if equipped).

1. Remove the instrument panel sound insulator panel (if equipped).
2. Disconnect the electrical connector from the blower motor.
3. Remove the blower motor screws.
4. Remove the blower motor from the HVAC module.

1. Position the blower motor and install mounting screws.
2. Connect the electrical connector to the blower motor.
3. Install the instrument panel sound insulator panel (if equipped).