Toyota Repair: Check Engine light Code 51 and Heat, vacuum hoses, toyota celica

Question
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Followup To
Question -
I've got a couple questions but they may be related to the same problem.  I have a 1988 toyota celica convertible.  3SFE engine 5 speed manual transmission.  I have an Engine Light Code of 51.  In my manual it basically says take it to a mechanic to diagnose.  It also talks about the A/C switch or amplifier being the possible problem.  I also have a heat problem.  I have heat but then when I moved the thermostat to cold and back to heat I don't get the heat back.  I disconnected the battery and reconnected it and got the heat back.  Then again when I moved the thermostat to cold and back to heat I don't have heat.  That sure sounds like an electrical problem and maybe has something to do with A/C switch issue which would explain code 51.  If you can shed some light on any of these issues it would be appreciated.  Thanks again.


Answer -
Does this model celica have the push button A/C Heater controls and is it auto climate control(auto a/c) or does it have the manual knobs that you move to control the heat and A/C and manual climate control.


It has push buttons to turn on the A/C heater controls.  Then there is one lever that you slide back and forth from left to right to adjust the temperature of the air coming out of the vents.  

Thanks.

Answer
A very common problem with the push button controls was the in dash control unit itself, this is a kind of complicated system and is controlled by a small computer in the dash control,the controls on the heater/a/c are controlled by servomotors which are controlled by vacuum signals being input from the control panel.The most common repair was to replace the in dash control unit which is very expensive( about $800) however there are other possible causes such as a vacuum leak in any of the vacuum hoses or one of the servomotors.
In any case repairing this will be very expensive.
The best advise I could give is to pay the toyota dealer the diagnostic fee to tell you what they recommend to repair this and then go from there.