I replaced an old mechanical thermostat with a Honeywell CT8602 programmable one a few years back. The airhandler portion of the system is a Trane TWV024B140 and is connected to an outside A/C unit (and a heat exchanger for the hot water tank but that is another post at a later date). The A/C system and air handler have been working fine and since I am is south Florida I never checked the heat before or after thermostat change. It has gotten a little cool here in the past few days so I did a little checking and there is a heating unit inside the air handler but the thermostat will not control heat. The terminals on the airhandler are W1, Y, W2, B, T, O, G, R. The terminals on the thermostat are R, Rc, O, W, Y, G with R and Rc connected together. The connections between the airhandler and (thermostat) are R (R), W1 (W), G (G), and Y(Y). The Honeywell instructions are pretty clear and from what I have been able to figure out it is installed correctly. I have searched the Trane site and discovered this airhandler is a commercial unit and I am unable to obtain manual or wiring diagram to verify installation. Any help would be appreciated.

 

Not sure just what you have there for heat. Is this a heat pump with strip heaters in it,are just electric heat?? That air handler when you say it has a R G O T B W1 W2 Y

R is power G is fan relay O is cooling changs over B is

for a heat change over

T dont know here W1 first stage heat W2 auxiliary heat relay
Y compressor
Id find the old tstat and see what you have on it

Like you can have an OT for outside temp you dont use and on a heat pump you can only use O or B not both of them. That hot water recovery tank for hot water dont have any thing to do with this. If thats what it is. Post back in samee postwith more info on the units and we can help Hey it did get cold down here in FL didnt it 38o here

ED

 

The heat is an electric unit (Trane BAY96X1405) inside the air handler. After further investigation the problem seems to be the fan control. With the A/C on (thermostat set to cool) and the fan set to auto the fan comes on when the thermostat senses a high temp. The wiring that appears to connect to the outside A/C is Red (on Y term of airhandler) and White (on B terminal of air handler). When I select heat on the thermostat with the fan on auto nothing happens except a relay in the thermostat energizes when the temp goes below the setting. I have since turned the fan to on and the heating works. I suspect the heating element will not turn on with out airflow but do not know why the fan does not turn on when the temp drops below setting. There are two cables connected externally to the air handler. One apperas to go to the A/C unit with two conductors Red on the Y terminal and White on the B terminal. The second cable with 5 conductors to the thermostat are connected to W1 (White), Y (Blue), G (Green), and R (Red). The yellow wire is not connected and has an open (suspect the blue was substituted vice run new cable). There is also a set of conductors (both brown) that are internal to the air handler and go to the heating unit. The are connected to the R and B terminals. The W2, T and O terminals on the airhandler are not connected to anything. The R and Rc connections in the thermostat are jumped. I suspect that the outside A/C unit causes the airhandler to move air but without prior experiance with A/C units I don't know the other end of the circuit. I moved from up north many years ago in part to avoid having to deal with heating systems so 36 degrees here was not cold it was cooler than I would have liked. I know the heat exchanger for hot water is not related to this problem but it has been disabled and will likely be the subject of a later post when the weather warms up some and I can get a better look at it.

Thanks,
Bob