Good evening,
Recently I was servicing a MrCool Furnace that would not start up. I came to the conclusion this was due to a faulty control board. I’m fairly confident in my diagnosis, but I would like to get other opinions before I inform the customer that he needs a new control board.
Model #: MGM95SE070B3XA-2
Upon arrival I was told that the furnace had yet to run since turning it on for the season. The thermostat was set to 85 degrees and displayed as if the furnace were running in heat. When I got down to the furnace, I first checked continuity on both ends of the thermostat wire so that I could rule out the possibility of any short between the t-stat and the furnace. I did find to have continuity through each wire. I then measured and confirmed accurate high voltage readings of 120V inside the furnace. After that, I continued to follow my voltage until I came to a 3 AMP circuit breaker located in between the transformer and the incoming high voltage. That breaker was tripped, so I reset the breaker. After resetting, I could hear the humming of electricity coming from the transformer. After a few moments, the breaker tripped once again; so that is when I decided to bypass the circuit breaker so that I may try and get power to the control board.
After bypassing, I was able to read accurate voltage on both the high and low sides of the transformer. I checked all over the board and was unable to get any sort of reading whatsoever. Before diagnosing the control board being faulty, I wanted to try one last thing to be sure. So I removed the existing transformer and installed a new one identical to the original. After the new one was installed, I checked voltage and had accurate measurements on both ends…still no readings from the board.
Any opinions or suggestions would be greatly appreciated.
Thank you and have a great evening everyone!