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99'accord, heating controls broken

on my 99 accord (v4, lx) i am unable to change temperature
i.e no matter whether the knob is turned to cold or hot, it stays hot.
a/c doesnt work. fan still works.
defrost front/rear is not working…
its like the heating/ac controls are not working.
any tips/suggestions on things to try?

If it was my car…I would take the control panel out and head to the nearest salvage yard.

It depends on how the hvac is configured. On some vehicles this could be something simple. So it’s worth the time to take a look under the hood up at the firewall. Do you see two rubber hoses going through the firewall, about 1/2 to 3/4 inch in diameter? Next to each other? If so, one is likely the hot water hose going to the heater, and the other is the cool water hose coming from the heater? The amount of heat released into the passenger compartment is proportional to the amount of hot water flowing through that hose. The heat control is a valve which limits the flow. When the valve is 100% on, that’s max heat. When 50% on, that’s warm. And when off, that’s cold.

Do you see any mechanism in that area that moves when the heater control is moved from cold to hot? If so, you might can spot what is wrong. The cable has come loose, a small metal pin is bent or brokens, etc. If you don’t see anything like that, then that proportioning valve is probably under the dash, and you’ll need help from someone familiar w/the set-up, or refer to a repair manual specific for the car. It’s also possible this isn’t the valve that’s the problem, but a blend door that is stuck. Again, you need the specific info for the hvac configuration to decide what to do. But no harm done to look up underneath the dash and see if you can see something sticking while a helper moves the controls.

Edit: I should add that there was a thread here a while back about cheap fixes people do on older cars, and one poster, to fix this same problem on an older car, said he’d made a hole in the dash, ran those two aforementioned hoses through it, installed a water shut off valve like is on your house for the outside hose, and adjusted the heat using that valve.

Thanks @GeorgeSanJose for your detailed explanation. When I first read the post…I just assumed the controls were shot. Besides…I’ll use any excuse to get down to the salvage yard and poke around. That or a trip to the hardware store.

appreciate the helpful suggestions… i couldnt spot anything obvious.
car shop says i need a new control panel…
need to think what to do next…

Reminded me. On my 59 Pontiac, the guy before me had taken all the heater controls out of the heater box so that you couldn’t shut the heater off. In the summer I would just clamp off the heater hoses, and replace them again for the winter. Never thought about a shut-off valve.

The problem is the factory service manual or the equivalent is the only one that would have detailed schematics of the system and trouble shooting guides. As suggested, just have to start taking a look at all the controls and make sure your vacuum hoses are ok, the controls are hooked up and the doors work. There also could be an electrical/vacuum HVAC control under the dash somewhere that could be faulty.

OP could visit the local public library, they may have the HVAC configuration in a “Motor” manual in their car repair section, or they might subscribe to AllData database (technical info used by car mechanics, covers most make/model/years), which would have the diagrams and diagnosis and repair procedures. Also, OP can subscribe to a DIY’ers version of AllData themselves, specific to that particular car, for a small yearly fee.

here is a pic of the door motor drives

i searched and found this post at
see the 13th post in the thread…
i am thinking it should be worth a try!