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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22636
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Have TDD100C Trane furnace and A/C that has blown 5 Amp fuse

Resolved Question:

Have TDD100C Trane furnace and A/C that has blown 5 Amp fuse when switching from A/C to heat. Works fine when set to A/C. What could be my problem? Jerry
Submitted: 7 years ago.
Category: HVAC
Expert:  BillyHvac replied 7 years ago.
That means there is a short in the white wire somewhere or a short in the furnace. Unhook the wire form W at the furnace and try again. If it does not blow the problem is in the thermostat wire. If it does blow the short is in the furnace.
Customer: replied 7 years ago.
Removed W wire and turned on furnace and fuse did not blow. Do not think problem is in wires because when Thermostat in Cooling mode the air condition works fine and blower motor is working in A/C mode. Please advise! Jerry
Expert:  BillyHvac replied 7 years ago.
with w removed at circuit board we can also jump r & w terminals and see if fuse blows.
Customer: replied 7 years ago.
I disconnected W wire at stat(hooked up W wire in furnace) and with stat in heating mode the red indicter light binked slowly – fuse did not blow. No heat. What next! Jerry
Expert:  BillyHvac replied 7 years ago.
Now take stat top off again and touch the white wire to Rh and see if fuse blows or furnace starts
Customer: replied 7 years ago.
Placed stat wire W to Rh and fuse blew! Only have 0ne fuse left!
Expert:  BillyHvac replied 7 years ago.
the short is in the furnace. You could possibly have a bad heat circuit in the circuit board or another damaged component. This may require a tech with a test meter to find
BillyHvac and 2 other HVAC Specialists are ready to help you
Customer: replied 7 years ago.
What are the numbers for the circuit board and heating elements? Might order parts on internet. If heating elements--How can I look at those elements for visible defect? Had main limit switch replaced in May at a cost of $214 and switch on internet sold for around $50 yet the repair person charged $150 for the part.
Customer: replied 7 years ago.
Found number for circuit board on internet for $131
Expert:  BillyHvac replied 7 years ago.
That is a good price. Let me know how it turns out
Customer: replied 7 years ago.
Ordered part - Thank You - will hit accept when part arrives in 4 days and part corrects the problem! is this ok!
Expert:  BillyHvac replied 7 years ago.
Thats the way it should be....I wish you luck
Customer: replied 7 years ago.
Billy - Circuit board replaced after purchase on internet and the problem did not go away. Today furnace guy here and he found short in the main limit switch. When he megged the switch the short did not show. But he claims the switch was the short problem. I had that switch replaced in April so never expected the switch to be the problem now. Bill $239, $24 more then last time they replaced the same switch. Tks! Jerry Will accept your service after your reply.
Expert:  BillyHvac replied 7 years ago.
I am very sorry you have had such unfortunate situations with the furnace. I take it very serious when I find I did not supply advice that helped or saved money. I apologize.