My house which was purchased from a bank (foreclosure) was originally wired with both central air and heater (forced air). But when the previous owner left, he took the air conditioning unit. The heating unit (a furnace forced air in the attic) stayed. No modification was made to the wiring as far as I know. Currently the existing thermostat has difficulty with some settings especially cool/fan (ends up blowing hot air) and heating up the house.
I am ready to switch the existing thermostat to Ecobee 3 lite and wonder if there is anything I should change in the thermostat wiring now that the AC unit is no longer connected.
Best Answer
For now the only wires that are needed are Rh, W and C. The G terminal operates the fan. It sounds like you don't want to be operating the fan. You can simply connect the G terminal and use the fan at your discretion. Leave the Y terminal disconnected. If and when you want A/C you simply pull the stat off the wall connect Y and reinitialize the ecobee. When they start they check what wires are connected, and if you have a wire connected to it that doesn't go anywhere it may cause minor problems for the ecobee.
In regards to the A/C replacement referring to Jim Stewart's comment. A new air conditioner will be using 410a refrigerant. You don't want to reuse the old copper lines because
Lines used on r22 are not compatible with 410a
If the old unit was 410a, the lines need to be sealed from atmosphere when disconnected.
Flush kits are available to clean the lines (I would never use one, I always replace the lines)
So the cost of replacing it would be very close to the cost of a new installation. The electrical has been run. But it may not be done right.