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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Rheem Criterion II furnace that is about 16 years

Customer Question

I have a Rheem Criterion II furnace that is about 16 years old. It's been working problem-free for a long time. The last week ( with cold weather) the 3 amp fuse on the circuit board keeps blowing. I've replaced it a couple of times. It works fine for awhile then blows.
Submitted: 11 months ago.
Category: HVAC
Expert:  airheatman replied 11 months ago.

If fuse is blowing there is a short somewhere in control circuit Could be in thermostat, wiring between units ,furnace board or internal components. Is there any patter as to WHEN it blows? Examples

1. Only when turned to AC

2.As son as fan comes on

3.When gas valve opens

Customer: replied 11 months ago.
I haven't been able to catch the fuse actually blowing. Anew fuse was put in Thursday afternoon. It worked fine until last night. Before going to bed I noticed that the t-stat was blank. I put in a new fuse in then. The furnace is still working as I type this.
Expert:  airheatman replied 11 months ago.

Shots like this can be hard to find since not blowing every time not comes on.Even when blowing everytime often takes several fuses as we try different things to eliminate the short.The way to determine is first look for any nicked or chewed wires that may be touching in control circuit between units and thermostat. Then by disconnecting components until it no longer blows.My recommendation is to try to monitor it to see if there is a pattern that might indicate what is changing that would cause the short.

Customer: replied 11 months ago.
Ok - I'll monitor and look for a pattern. Thanks :-)
Expert:  airheatman replied 11 months ago.

Let me know and we will see if we can determine what is creating short.

Customer: replied 11 months ago.
the furnace fuse blew again today (Sunday). I opened up the furnace and installed a new fuse. When I pushed in the plunger-like safety switch (usually depressed by installing the furnace door panel) the fuse blew instantly. I installed another fuse. Before depressing the safety switch, I unplugged the two wires (solid orange and red with white stripe) (see furnace 2 image). these wires are near the top left of the furnace box, near small blower that pressurizes the vent stack (see furnace 1 image). I then depressed the safety switch, let it run for about 20 seconds, let go of the switch, plugged the two wires back in and closed up the furnace. It has been running all afternoon and evening.I included an image of the circuit board in the furnace (see furnace 3 image). the fuse is on the lower left part of the board, purple, with a white '3' on it.
Expert:  airheatman replied 11 months ago.

Do not see the furnace 2 image

Expert:  airheatman replied 11 months ago.

Only seeing image 1

Customer: replied 11 months ago.
here is furnace image 2
Customer: replied 11 months ago.
here is furnace image 3
Customer: replied 11 months ago.
let me know if you can see these - Thanks :-)
Expert:  airheatman replied 11 months ago.

Ok the one in image two is a high temperature limit switch.Disconnecting wires would just break circuit in the control wiring

Expert:  airheatman replied 11 months ago.

I honestly am suspecting you may have a control board going out.

Customer: replied 11 months ago.
is that a difficult item to replace? how would I find a replacement board?

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