Heat & A/C at the same time

[allseason]

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.

[kurt]

Vertically oriented townhouses are notorious (around here anyway) for having lousy AC at the upper floors.

Sounds like someone jackwired the system so they could control the AC at the upper floor stat.

[Marc]

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.

Marc

[Rob Amaral]

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..

[allseason]

I believe Kurt is correct. The tenent said that the upper t.stat was for the AC and the lower for the Heat. I told them it's wrong.