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Heat & A/C at the same time


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At a town house today with a 2013 Lennox cat I furnace with a/c on top. 2013 Lennox comp/cond. Two thermostats, one on the third floor, one on the second floor. I turn on the a/c on the third floor, get cold air on all three floors. While that's running I turn on the heat on the second floor thermostat, furnace lights up. No zone dampers, only one unit. I run outside and the comp/cond is running at the same time the burner is firing. Looks like multiple thermostat wires to the board. If one thermo. is hooked to the a/c and the other to the furnace can both run at one time? First time for me. I turned off both thermostats as that's where they were when I started.

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Mis-wire in the control circuitry, defective thermostat control card for multi-unit systems, or some humidity control feature particular to that system model.

Definitely call it out for further eval by an HVAC guy familiar with that make/model system, just to be safe.


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Short story: 1940 house expanded into huge capt-of-industry castle. I inspect while workers are still completing many items, including HVAC, etc. Could not test HVAC. 6 zones of Cooling/Heating (Forced-Air/gas, electric split ducted systems).

1 year later.. Capt's wife calls me with dire problem: "We are going crazy trying to control the cooling/heating.. too hot, too cold,"

I tell them to turn all zones off nite before I go and let me go through house.

I survey all units, name them, name all t-stats, compressors, furnaces.

Then I just turn one on... and go find the furnace/compressor.

They had miswired the entire place... little bedroom thermostats were connected to systems meant to condition huge family room and vice versa..

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