1988 Camry Heater Cycles Between Heat & No Heat

[lashby]

I am new to this but don't know where else to go. '88 Camry LE, 4 cyl, auto, 194,000 miles. Heater/AC dash control panel has electric pushbutton controls. Few years ago heater began cycling between heat/no heat. Works good until car runs about 30 minutes, then begins putting out cold air. In AC mode, unit puts out cold air until car comes to a stop, then cold air stops. Took it to Toyota dealer and was referred to their contractor who takes care of those problems. After $350 still have same problem. System has been flushed/filled, thermostat changed, electric switch (small black plug-in box, maybe 2x4 inches, kind replaced. Took it to another place (non-dealer). By observation, the cable that runs to the heater control valve on the firewall will open/close by itself with dash heat selector in the heat position. Don't think it should do that. Mechanic installed a manual cable (manual choke cable) from the dash to the heater control valve in hopes that keeping the heater control valve open will keep the hot stuff flowing through the heater and keep the heat on. The cable does keep the valve open but the heat still cycles although you do get some residual heat from the hot fluids still flowing through the heater. Because everything under the dash is electric, the mechanic is at a loss of what to do but is determined to figure out a fix. Anyone have a similar problem or advice? Have had this car since new and it still runs great - just getting really frustrated with the heating system. Appreciate any info. P.S. This is my first time on the NT site so be gentle. Thanks.
Ran manual cable to

[davesmith76]

My '88 Camry 4cyl. auto has developed the same problem. The heat will stay on very steady for the first half hour or so. Then it will just randomly decide to switch off on me. It is a sudden shift, like someone was throwing a switch. I figure that one of the vent flaps is losing its seal and falling down, bypassing the heater core and letting in the cold air from outside. Has anyone had this problem and fixed it? How is it fixed?

Sometimes I can get it to come back on for a while if I push the button for outside venting real hard, or I can get it to come back on for a while by hitting the dashboard real hard a couple times,

Any ideas for a permanent fix? It is very cold in Michigan right now.

Thanks,

Dave

[davesmith76]

?

[celicastyle88]

I have the same problem on my '88 Celica. It cycles between hot and cold. I would really like to find a solution to this for Canadian winters. Any help?!? Sorry to bump such and old post...

[es250nut]

Had the same problem in my 87 with the electronic controls.

After much fighting with it, I discovered the sliding rheostat was the problem. It was leaving an open circuit and so the servo that opens and closes the door to the heater core stays closed, leaving whoever was in the car to freeze. I fixed it by re-soldering the contacts on the back of the board. About 2 years later it did it again. This time I went to the junkyard and purchased anoter control unit for $8.00 and It's worked fine ever since.

As for the A/C, if the idle of the car doesn't stay around 1000rpm while it's on the A/C will drop out. My car will usally drop to 700rpm at a stop and the A/C drops out unless I keep my foot on the gas and brake at the same time. I figure the idle kick up circuit/valve for the A/C needs to be looked into, but since it only happens when I'm at a stop I don't figure I need to worry too much about it yet.

[celicastyle88]

Originally posted by es250nut
Had the same problem in my 87 with the electronic controls.

After much fighting with it, I discovered the sliding rheostat was the problem. It was leaving an open circuit and so the servo that opens and closes the door to the heater core stays closed, leaving whoever was in the car to freeze. I fixed it by re-soldering the contacts on the back of the board. About 2 years later it did it again. This time I went to the junkyard and purchased anoter control unit for $8.00 and It's worked fine ever since.

I'm on my 3rd heater control panel that I've picked up from a junk yard. All have the same problem. I resoldered one of them, and it lasted about a month.
Where exactly did you resolder on the back of the board?

I have the same problem, you can hear the servo motor working and doing whatever the heck it pleases.

[es250nut]

Sorry about the delay... Had to go to work.

What you need:
Phillips screwdriver
Continuity tester or Ohm meter
Soldering Iron

First, pull your Climate Control out. Slide the heat control all the way to the Right/Hot setting. Using your Continuity tester check to see if the two pins circled in orange complete a circuit. If you slide the control over, the resitance of the circuit should get higher (bulb on tester will dim more as it moves to the left/cold) until there is an open circuit. If this works as I describe it, the problem is not with the Climate Control. Otherwise remove the circuit board from the plastic case and fold the connector board over so you can resolder the joints I've circled in orange. (You can also test the cicuit from these solder joints to see if the slider is still good.

You can also take a piece of wire, and with the ignition on, jump the corrisponding pins in the climate control plug of the cars wiring harness for the heat control. If you can hear the servo motor open the heater door then that part of the circuit is fine. If you can't get your slider control to work, you could put a seperate rheostat on that line to operate your heat control seperate of the Climate control. If you can't get the servo motor to work that way you will need to check your climate control fuses and servo itself.

Hope this helps, Let me know how it goes.

[celicastyle88]

Wow, thanks for the pics and explanation. Can't wait to try it. I'll post my results.

Another quick question. I purchased a used heater control panel from a junkyard. It is the same, except for this one has A/C on it and mine does not. Will the circuits be the same on the heater control panel, obviosly it will have the "extra" a/c button but other than that will it work fine with a car not equipped with A/C, or do I need to find a heater control panel without A/C?!?

Thanks.

[es250nut]

I don't think that should matter, just as long as the plugs are the same.

If your car doesn't have Air Conditioning then that button won't do anything. As far as that goes, there might even be a "blank" in your original control panel where an A/C button would normally be.

[MCTOY]

Hey es250nut,.......
Just wanted to say "GREAT JOB" in taking the time to post pics etc.
I was gonna post the same info you gave, but honestly don't think I would have done all you did to answer it. It is all to frequent that on all these sites that someone (or 6 someones) will just reply "Do a search!" Especially to newcomers. ATTABOY man!
MCTOY

[es250nut]

Thank You. I firmly believe in "You get what you give."

[es250nut]

Bump

It's getting cold, this thread is more relavent now...

[alex86]

uhm how do i get to that circuit and if i pull it out how would it get current if u pull out all the power cables nd such. im a noob at electrical for cars(more on computer stuff) but its basic knowledge. dont want to b an ass but when u pull out power cables no electrical current goes thro meaning no reading could b read so i dont really get the point in checking it with the tester.

if im wrong then dont mind me just scratching my head too much but ya just trying to find out where exactly i find that circuit board and hopefully i really wont need a soldering iron

[es250nut]

If you take the climate control panel out, the circuit board that you see in the picture is the one located in the back. A continuity tester has it's own power supply. If it's an Ohm Meter it will measure the resitance of the circuit. If it's just a simple light continuity tester it will probably have a AA battery and a flashlight bulb.

[alex86]

seems hard as hells with the soldering iron nd stuff but ill see what i can do thanks for clearing it up for me.

but good job on the help