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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7791
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Our house is a relatively recent (5 year) rebuild with all

Customer Question

Our house is a relatively recent (5 year) rebuild with all new hvac components. Never any issues - 2 zones, excellent cooling/ac in summer and excellent heat in winter. Last night the system started blowing heat when the setting was on cooling (room temp 73, cool setting 68). I replaced batteries and toggled thermostat (Honeywell) and cooling came on. About 2 hours later system was blowing heat again. Is this a thermostat issue, air handler unit issue or other. Very strange given great performance history of system. Thank you.
Submitted: 6 months ago.
Category: HVAC
Expert:  airheatman replied 6 months ago.

Issue could be a number f things.Lets start by getting me model on units so I know what type of system we are dealing with.

Customer: replied 6 months ago.
Does this help. Not currently at home.
Customer: replied 6 months ago.
Expert:  airheatman replied 6 months ago.

It helps some. It tells me you have a conventional non heat pump system, Do you know if the furnace is gas or electric?

Customer: replied 6 months ago.
We have a large air handler unit for each zone, so I suspect electric. Plus the air handler plugs into the wall.
Expert:  airheatman replied 6 months ago.

OK if electric the issue could be a heat sequencer somehow getting energized.

THe next time it does this, disconnect the thermostat wires at the air handler and see if it stops.If so issue is external such as thermostat if it continues to blow hot, issue is from a sequencer or something in air handler.We can go from there diagnosing.We would need a meter to troubleshoot. If you have a meter let me know .If not you can get an inexpensive one at Walmart for about 15 bucks if you would like to troubleshoot and I would be happy to guide you.

Customer: replied 6 months ago.
Ok. I'll get back to you by tomorrow (hoping I can try as you suggest tonight). Thank you.
Expert:  airheatman replied 6 months ago.

Sounds good.