Air handler won't turn off when Cool setting is on with Auto fan. The compressor works fine and turns off correctly. Air handler works fine when heat setting is on, I.e. Turns on and off with heat. Curious what is different with cool setting.

Regular thermostat wiring - red, green, white and yellow.

 

Welcome to the forums.

See if the blower stays on with the thermostat disconnected.

The furnace controls the blower in heat mode.
The stat controls the blower when in cool mode.

Power on the green wire turns on the blower.

 

I turned it in cool setting and increased temperature. The compressor turned off but the blower kept running, as instructed I pulled out the thermostat completely to disconnect but the blower still kept running. Is this what you meant by disconnects?

Not sure if makes difference, the system is hydro duel zone (upstairs and downstairs) with two compressors and single oil furnace.

 

Not sure what you mean by hydro dual zone. I need to know EXACTLY what you have to help you.

It sounds like you are mixing two independent systems here.... an A/C system and an oil furnace.

Has this setup worked in the the past and now has a problem ?

 

Hi Pete,

Sorry for not being clear. The house has two zoned AC/Heat system with two thermostat and two air blowers, one for upstairs and one for downstairs.

For Cooling - There are two compressors that supply to upstairs and downstairs air blowers respectively.

For Heating - There is a single furnace that heats water that is supplied to both the air blowers. This is what I meant when I said hydro air.

The issue I am having is for upstairs air blower. It used to be working correctly for both, heat and cool cycle. But now, it works perfect for heat setting but when cool cycle is selected, the air handler won't turn off once the temperature is reached. I have to shut down the whole system from switch board.

I tried your suggestion this morning where the system was turned on cool and when the temperature was reached the compressor turned off but the blower kept on running. I pulled out the thermostat (is this what you meant by disconnect?) and the blower still kept on running. After few mins I replace the thermostat again and still no change. At that point I turned off the unit from switch board.

Any other test?

Thanks for helping..

Subhav

 

Make and model numbers would help.

 

That's not what I would call a "two zone" system. That is two systems.
One A/C system, hot water coil and stat for the first floor
One A/C system, hot water coil and stat for the second floor.

You've got some kind of specialized system. Your thermostat is controlling the air handler and it also needs to control some type of zone valve for the heat. Somewhere..... two systems.... A/C and heat are being combined..... it may be relays.

A make and model for the air handler is needed.
A picture of any stat wiring could be helpful too. http://www.doityourself.com/forum/el...-pictures.html

 

Sounds like an interesting system. I wonder if the problem could be a stuck relay inside the air handler cabinet? OP have you tried the smack test yet? Don't be skeered of it man give it a couple of good strong wacks "HIT IT LIKE YOU LIVE MAN" and report back soon

 

Air Handler - Trane TWE036C140A1
Relay - RIBU2C

Attached is picture of thermostat setting.

I gave the relay a whack and started the system. Still no change. I noticed that both both relay lights were off when the system was on, is that normal?