RUUD blowing fuse

[emmerat]

Hello,

I have a RUUD UGGD - 12 ERCMS gas furnace with a 4PRL-060JEZ Heat Pump. It has been off for a few weeks....haven't needed the A/C just yet. Anyway, in March, the 3 amp fuse on the internal board in the furnace blew....the system was installed 2 years ago, and I didn't hink much of it. I replaced it and everything worked fine. So, I went to start it yesterday, and nothing. I checked the fuse, and sure enough, its blown. I replaced it and it blew again immediately. Where should I start my search? Thanks for the help.

James

[dkpd1581]

Check for shorts to ground or wire to wire shorts in the t-stat wiring.  Look for abraded insulation where the t-stat wire penetrates anything sharp or metal.  Check to make sure you don't have a defective contactor that is sticking open and causing high amp draw because it cannot close. 

With the t-stat turned off, try and run the fan first.  If it doesn't blow the fuse, the run the heat, if nothing then run the AC.  Where ever it blows that is the circuit to start checking first.

[emmerat]

Hey DKPD,

I ran new wire when we installed the units, and everything looks okay...no obvious shorts. I pulled the t-stat head off inside the house, and inserted a new fuse. Without putting the blower door on, I can press the blower door safety switch (makes sure the door is in place), and the fuse pops. Is this the contactor you're referring to?

Thanks,

James

[dkpd1581]

You have a couple of options:

1.  You still have a short to ground or wire to wire short

2.  You have low voltage wiring miss wired to the board or t-stat

3.  You have a defective board

4.  You have a defective t-stat

Remove all the low volt wiring to the board and check to see if it blows - if so #3

Ohm out the t-stat wiring to ground then wire to wire  if any continuity then #1

With all t-stat wires off board and t- stat jumper wire (one by one in this order) R to G on the board, then continue with R to Y, then R to W1-W2-W3 etc.  Where it blows is the circuit to check further.  Then #3.

If the issue happens on the Y1 test, check the condensing unit contactor as part of the system check.

Attach only the R and C terminals to the board and t-stat and check if it blows.  If so then #1, #4

Attach (in this order) and test each individually G, Y1, W1.  If it blows then #4