Need AC Help

[Monkeyman2500]

Ok I'm pretty mechanically inclined so need a little DIY help. Unit is a Bryant model FB4ANF036. The blower will not shut off and heat coils come on in cool mode. The 2 pole switch to the cools has been replaced and I have replaced the circuit board. It was running fine till last month. I'm stumped. Any advice would be very appreciated.

[RED333]

Check the thermostat wires

Yellow wire is for AC

White is for heat

Green is for the in door blower

Red is power to the thermostat

 

Sounds like the wires got crossed some where

Edited July 30, 2015 by RED333

[peejman]

This just spontaneously happened? Running normally one day, then blower motor and heat coils acting screwy? If that's the case, makes me think something internal melted and caused the crossed connections.

[bersaguy]

MY unit did same thing or very similar about 3 weeks ago. Land Lord put in a new thermostat and problem was solved. Old thermostat was send false messages to the unit causing the blower to run constantly and heat and a/c was alternating back and forth........ :2cents: 

[Monkeyman2500]

Yea just happened out of the blue. I disconnected the heat coils to solve that for now. The blower will run normal for a while after I shut power to it for a while. Then gets stuck on run after a while. I'm starting to suspect the thermostat too Bersa I don't really know what else to replace. It's an older unit so pretty simple compared to the new ones.

[Monkeyman2500]

Also as far as I know the only thing inside the unit that controls the fan coming on and off is the circuit board.

[peejman]

If you replaced the circuit board and are certain you got the correct board and installed it correctly.... the only other thing that comes to mind is the t-stat.  I'd at least remove it and check it out for damage. 

 

If you replace the t-stat, check out the programmable ones.  They cost a bit more, but are nice and can save you a few bucks in energy costs. 

[Monkeyman2500]

Yes the board is correct one and installed properly. At this point it could only be three other things. Limit switch, transformer, or thermostat. I may just replace all three. I'm actually still not sure where the limit switch is though. For its age this unit is still in great shape and I figure putting a couple bucks into it can't hurt in the long run.