Good day. This is my first post here. I have been in the hvac/r field for about 6 years now. I have came across something that I have never incountered before. Here is the run down.
My brother-inlaws ac unit is an older coleman single stage electric/gas package unit. He had a new heat exchanger put in last year. Ran great during the winter months. Switched to cooling mode and got nothing. I showed up with meters in hand. I didnt have control voltage. Replaced the transformer. The control voltage is now back. I can get the indoor fan to run, the gaspack will run, but when you switch to cooling, you get nothing, but a blown transformer. Replaced the transformer, and put an inline fuse in to protect it. I can get the compressor to run by manually pushing in the contacts.
I put my meter on the red wire and the yellow and had continuity. Jumping the gun, I pulled a new wire thinking there was a dead short in the jacket. After new t-stat wire pulled, still have continuity between the two wires. Now, If I pull the moulex plug of the control board, I lose the continuity between the red and yellow wires. Also, if I remove any wire off of the contactor, I will lose the continuity also. I have replaced the contactors, the start/run caps. I have pulled the whole harness out, there is no chared or broken/skinned wires. My brother inlaw is limted on money. I pulled the boared, and checked it over. The board looks good, and works for everything, but the cooling. We also put on a new t-stat. Before I order a board, would anyone here know what might be my "gremlin".
Like I have typed above, I have never hit a bump like this. The only thing left in the cooling circuit that hasnt been renewed is the board. Any help would be greatly appreciated.