Hello, Hopefully someone here can shed some light on what might be happening with my system(s). Here is the chain of events that led up to the problem. I have a dual zone setup in my house . A 3-ton heat pump on the second floor (Lennox Merit series installed circa 1999) with CB29M41 air handler in the attic and a 3.5-ton on the first floor (gas backup) . For the first time this year we needed AC with outside temps above 85. So Saturday evening I switched the upstairs unit from heat to cooling mode. Instantaniously, the digital thermostat (Lennox 31M55) went dark. I removed the thermostat housing and 0 volts at red wire. I climbed into the attic, removed the cover from the air handler control box and reset 3.5 amp the fuse on the secondary low voltage side of the transformer. Replaced cover on thermostat and now it has power. I am able to energize the blower in the air handler from the thermostat but setting it to heat or cooling will not start the outside compressor. The thermostat just flashes heat or cooling and the fan runs. I checked the outside condenser and it is getting 28 vac at red wire on defrost board. The contactor and capacitor are new and tested fine. If I remove the thermostat and jumper R and Y , the outside unit comes on but in heating mode. Great...I thought, bad thermostat. I have the exact same model stat on the 3.5 ton system (the ac works fine on the first floor). I swap this stat on the second floor with the same results (still doesn't work). I take the stat off and put it back on the first floor system and voila the ac no longer works on the first level. No heat or collong just the cliking of the blower relay. WTF! Spent a total of 16 hours debugging this issue over the weekend. Now I have 2 systems that are inoperative. I reset both stats to factory default using he reset button. No luck. Running out of things to try. Please help and sorry for the length of the post.

Hello, I’m trying to figure out which wiring process I would use for the following setup and which system type I would define in the thermostat. A bit long…. I have a Lennox G61 2 stage furnace. I do NOT have a heat pump or AC installed. I am looking in to using the Honeywell TH8320U_1008 thermostat. I want to use the 2 stages of the furnace as well as be able to use and program the fan for regular air circulation. I know it’s a bit more of a thermostat then I need right now but in a couple of years I do plan on having AC installed so figured I would go with a tstat that could do it all now and be set for the future, as much as one can be anyway. I see there are the following wiring hookups on the furnace: W1 – Heat Demand from 1st Stage tstat W2 – Heat Demand from 2nd Stage tstat G – Manual Fan from TSTAT Y2 – Tstat 2nd Stage Cooling signal Y1 – Tstat 1st Stage Cooling Signal C – Thermostat Signal Ground connected to transformer and chasis ground R – Class 2 Voltage to tstat 1 – Error Code recall H – 24V Humidifier Output L – Lennox System Operation Monitor 0 – Tstat signal to Heat Pump reversing valve The Thermostat has the above with similar labels/designations and adds the following: RC – Cooling Transformer hookup jumpered with R by factory E – Emergency Heat Relay Aux – Auxiliary heat Realy L – Heat pump reset / System monitor O/B Changeover valve for heatpumps S1 - Optional Outdoor/Remote sensor S2 - Optional Outdoor/Remote sensor My concern is that I see several tstat options like 1h/1c 2h/2c 2h/1c etc as I do not have AC I am looking for something along the lines of 2h/0c what option on the thermostat do I use? Or do I have to basically just wire it up as heat only tstat? Tstat Options available: 1. 1 heat/1 cool conventional 2. 1 heat/1 cool heat pump (no aux heat) 3. Heat only 2 wire 4. Heat only with Fan 5. Hot Water Series 6. 6 Cool only 7. 2 heat/1 cool heat pump (with aux heat) 8. 2 heat/2 cool multistage conventional 9. 2 heat/1 cool multistage conventional 10. 1 heat/2 cool multistage conventional 11. 2 heat/2 cool heat pump(no aux heat) 12. 3 heat/2 cool heat pump(with aux heat) Do I wire the tstat & furnace up as 1. Heat only with fan(an use the furnace jumpers to run in a handicapped 2 stage mode), (tstat option 4) 2. 2 heat/1 cool (tstat option 9) I thought of adding the outdoor sensor as well. Would I gain anything with it or no? Even though I don’t have a heat pump or AC installed would having it help the tstat configure proper heating/blower use?