1988 Camry 4cy AllTrac intermitent heat

My '88 Camry 4-cyl. 5-SP ALL-TRAC with PUSH BUTTON HEAT and AC CONTROLS puts out heat intermittently. Most of the time it does not. The HVAC computers turn the heater valve on or off for unknown reasons without tracking the heater lever setting. :screwy: Whenever the computer turn the heater valve on there is heat coming out of the vents. Since it does work whenever it feels like it I suspect it could be a grounding problem. However I cannot find a grounding point for the HVAC I can clean and tighten. Does anyone have any idea where the grounding point might be? Is it in under the dash or under the hood?
I am in denial that it could be one of the control modules. They are usually rugged. Or the dash control unit itself. Both are way too expensive! The shop manual has no trouble shooting procedure to determine which one it might be for heat problems. Only the AC has a trouble shooting procedure. I do not even want to go there for the moment. The modules are about $200 each and the dash control unit is $600. Buying on a hunch could get very expensive! :shakehead

The coolant is fine and the thermostat was replaced about 10,000 miles ago. The car has only 95,000 miles and has practically no body or fastener rust.
All Visible grounding points have been NO-CO coated (the red battery terminal protector/conducting stuff) or have had electrical grease applied to prevent corrosion of connectors. With winter coming it will get rough here in NH for anyone in my family to drive the car. Help!

Identicle to the problem on my 87. In my case I can push up or down on the temp control slider switch and get all the heat I want. Let go and I freeze. I can hear and see the blend door actuator activate on its own. Bad switch in the control panel. I plan on pulling the panel apart and attempting to fix the switch...when I get motivated.

RIP,
Very interesting! In a denial mode this is not what I wanted to hear. From what you are leading to my options are:

A) fork over $600 to Toyota for a new control panel and wrestle with the R/R of the panel.:shakehead
B) Find a used panel - would be the first used part installed on this vehicle. Some used part are priced just as outrageously if bought removed from the vehicle. In a wheel chair now I cannot remove them myself anymore.:nono:
C) Remove the panel covers and try to use contact cleaner. I have already tried this but without removing the panels I could not tell if I hit the right spot. If this fails remove the control panel and try to surgically replace the switch. Finding a suitable replacement is the problem.
D) Add a separate control cable and bypass the control panel circuitry. Not a real clean solution for a near showroom vehicle.:eek:

Hard to tell at this time but the switch you refer to is either a digital switch or an old fashioned potentiometer. From the schematics in the shop manual it appears to be the latter. It seems to be analog and not digital.

Unlike Toyota to leave out key debugging info from an otherwise excellent repair manual. The best I have ever had. Murphy's Law at work I guess.

Thanks RIP.
Radar24

On my '88 Camry 4-cyl. 5-SP ALL-TRAC with PUSH BUTTON HEAT and AC CONTROLS, A second appeal: Does anyone have any idea where the grounding point might be for the HVAC and the Audio in general? Are they under the dash, under the hood or under the center console? Or is it in all three locations? Any info would be extremely appreciated.

Toyota must have this info somewhere. Possibly in Technical Service Bulletins. I have no access to Toyota TSBs. It is not in my ’88 or ’89 Toyota written factory shop manuals.

Not as well written or as user friendly, my 97 S-10 shop manual shows most grounding points and their location in several diagrams. Toyota must have the equivalent grounding point and component location info somewhere.

HELP! Winter is finally coming to New Hampshire.

I found several cracked solder joints in the connector that has the Heat Control Switch pins. It sits on the small circuit card of the Heat/AC Control Unit or Module. The connector pin solder cracks can be seen with a magnifying glass on the part Toyota currently wants $600 for list. A lot of force is required to remove the connector and It seems removing the connector is cracking the joints.

It fortunately works now. It is going to be in the forties tomorrow and going lower.

This fix also stopped the AC led flicker. I found 7 pins with bad or suspect solder joints out of 12 populated pins in an 18 pin connector .