Air Conditioning/Thermostat Selection

POST the make and model # of thermostat

Is your thermostat such that you can access the wires connected to it while it is operational? you ought to slap a meter on there and figure out if the issue is with the thermostat not commanding the fan to be on or if it's in the furnace. If your furnace is like mine, the fan is controlled at different speeds for each of heat, cool, and manual fan on

- so at least in my case, if I were having your problem I'd be digging into the control board for the furnace not the thermostat. If however you have a single speed fan, it would likely be the thermostat. Which kind of setup do you have?

good luck

nate

Hi, Model of outside unit, furnace inside and your thermostat? Do you have a multimeter? How many wires are on the 'stat. When you are calling for cooling, you should see 24V AC between terminals on the 'stat R and G and again between R and Y(since outside fan runs you must see 24V AC here) If you don't see 24V AC between R and G 'stat is bad.

The first was an AprilAire 8363, the new one a Honeywell T87N

I'll do this test. However, the same problem has re-occured after replacing the thermostat. I can, however, access the wiring with the system in operation.

It sounds like a wiring problem somewhere. You already confirmed the fan and compressor are working, which is good. You just need to confirm if the wiring is correct. If it is, it could be a defective circuit board on your A/C unit.

Did this just suddenly happen to an existing installation, or was anything changed in the installation before the problem began, e.g. wiring, equipment, supporting electrical wiring, etc.

Furnace is Coleman 8.T and the AC unit is a Lennox HS18-411-5P.

If ( R ) on the indoor unit is connected to ( G ) on the thermostat and ( G ) on the indoor unit is connected to ( R ) thermostat then with the fan on it would connect G to R and with the cooling on R to ( Y ) with ( G ) OFF

Check the wire colour on the indoor Unit R - Y - W - G and make sure these are connected to the right thermostat terminals

By "Indoor Unit" I assume you mean the furnace blower?

yes, that is correct (or air handler if you have a heat pump)

nate

All of the wiring seems to be correct in accordance with the installation instructions. And still, when I turn the "Heat-Cool" switch "Off" and move the fan switch from "Auto" to "On" the fan comes on. If I put the fan switch on "Auto" and turn the AC to "Cool" the AC fan comes on and cold air enters the building, but wothout the fan, it does not move and the AC unit soon freezes up.

2- Check fan setting switch set to F

Will do. Thanks!

Mystery continues. I put the "G" wire on the "R" terminal, yes, the fan did operate without changing the switch position. However, as soon as I selected "Cool" the A/C came on and the fan in the house stopped again.

Cycling the system

Make up a jumper wire one foot long - bare a 1/4 inch at each end.

Will do. Thanks!

OK, will try it.

Hi, Sounds like you have bad 'stat/