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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Open gh limit device on freedom 80 furnace. if I pull out

Customer Question

open high limit device on freedom 80 furnace. if I pull out electric block and put back in ,it will run for a few days.
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

what do you refer to as electric block?

Customer: replied 1 year ago.
the connecting block with about 9 pins on the circuit board.
Expert:  Phil replied 1 year ago.

Hello, this points to bad gang connector (the one with the 9 pins) or a bad printed circuit board.

Turn the power off to the system then unplug and replug the connecting block about 5 times, that will burnish the oxide off any corroded pins... then try it, if that works, you have solved the problem.

If not, then

Stress test the printed circuit card.

Use a hair drier to slowly and gently warm the card to 120F(warm to the touch but not hot and not over140F)... if you get any change in behavior that means the card is bad...

A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it.

Constant expansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out.

It is also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometimes solve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course.

We can go from there without a time limit.