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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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5a fuse blows on heat only.....works fine in AC mode
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Customer Question

Customer: 5a fuse blows on heat only.....works fine in AC mode
JA: Thanks. Can you give me any more details about your issue?
Customer: Condo unit...Armstrong Air Ultra V Tech 80 unit
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Submitted: 11 months ago.
Category: HVAC
Expert:  Tim H. replied 11 months ago.

Hi, I'm Tim and I'm an HVAC expert here to help answer your question(s). Please provide all the information I ask for since I'm not onsite. At the end of our dialog you will be asked to rate my service, but please wait until then and all your question(s) have been answered satisfactorily. Thanks for your business!

Try taking all the thermostat wires off at the board (after marking their locations), and run a jumper wire from R to W at the board, then power back up. See if fuse still blows.