Limit Switches

[shopforeman]

Coleman Evcon Model #DGAT075BDD has blower staying on at all times and will not light gas furnace. Local repair man helped me out yesterday and sent me a new lower limit switch after diagnosing over phone for flash code 4. Replaced it and still flashing 4 so bypassed upper limit switch and it will still run fan at all times but gas furnace will light and run for one cycle then gas shuts off and fan will continue to run and will not shut off. I can turn unit off and back on and fan comes back on and after 30 seconds will fire up gas furnace and heat up until thermostat shuts off gas valve then fan continues to run all the time until I shut off (blowing cold air) rocker switch. Its Sunday so no one is open to get another switch but I did notice that the button was tripped on the upper switch but still would not turn on heater when reset. Still flashing 4 after first cycle of gas valve.

[Robert]

Hi,

You may have a bad integrated control board. It controls the blower motor and signal to gas valve.


It could also give a false code if faulty.



It should have 120vac and 24vac input and output with a call for heat.

It should have same input, but no output with a no call for heat and t-stat satisfied.



Thanks,
Robert