2 weeks ago my furnace wouldn't start. I checked and found corrosion on the main circuit board. When I pulled the board I found it was badly burned on the edge connector mainly around terminals 3 and 4. I replaced the board. The original board number was HH84AA021. The replacement is ICM 275. This is supposed to be a "Direct Replacement". I turned the furnace on and the inducer fan ran through it's cycle, I heard the igniter "clicking" and then there was a "Snap" and the 3 amp fuse on the new board blew. Then the blower fan turned on and ran. I pulled the new board out of the tin box it mounts in so I was sure it wasn't touching anything. I replaced the fuse and turned it on again. The fuse blew again. Problem is that the fuse on the original board was NOT blown....
I'm going to check thermostat wiring now.
Thanks in advance for any help........ It's starting to get pretty cold here in PA.........
Thanks for the quick reply Brian!
The installation instructions for the new board says that it is a direct replacement for my old board. When I installed the board I did it one wire at a time and the layout is identical. All terminals had the same designations. I do have alot of experience with multimeters. I checked all wiring on the 24 volt side and nothing is shorted to ground. I also checked the switches and found no problem. I'm starting to suspect the gas valve since everything works fine until there is a call for gas. That's when the fuse blows and all the wiring on the gas valve is 24v. Also the damage to the old board is at terminals 3 and 4. Terminal 3 goes directly to the gas valve. Terminal 4 goes to the inducer board. I removed the inducer board and saw no problem and the inducer motor works fine.
I removed the cover on the burner assembly and replaced the fuse again. I ran it through it's paces and the pilot lights and burnd for a while then the solenoid for the main gas valve clicks and a fraction of a second later the fuse blows. I think the valve is stuck causing excessive current draw blowing the fuse. Unfortunately I have to wait until Monday to get the part.
I'll let you know how it works out.
I replaced the gas valve and everything seems to work properly.