Any HVAC guys in here ??

[CaptNemo]

I'm having trouble with one of the Heat pump / gas furnace / AC units in the house. The numbskulls that installed them several years ago decided to use me as a guinea pig for a Lennox "Fuel Master 21" control unit. Apparently, this unit wiped out one of my printed circuit boards and the A/C is out in Mobile, AL. I have another PCB on order, but I want to ditch the Fuel Master and will need to do a little bit of re-wiring of the control circuits.

 

[CaptNemo]

Thanks !!

 

[rickairmedic]

Captnemo if you can get me model numbers off your furnace and air conditioner I can get some wiring schematics and try to give you some help rewiring that system .They dont call me the airmedic cause I like to fly around saving peaple .


Rick

 

[CaptNemo]

Ok, the new board is in and all of the connections EXCEPT the thermostat wiring.
I want to isolate / eliminate the Fuel Master Board but I see that the new PCB doesn't have the number of connections that the Heat pump and thermostat have. I realize that some of the wires will be doubled up on the terminal block, but it doesn't look like there is a Reversing Valve wire on the PCB. Is this done in the thermostat ?

Model of the furnace is a 8OUHG five ton Heat pump with nat gas piggyback furnace.
The thermostat is a Lenox 21J7201 There are 6 wires in the cable running from the T-stat to the airhandler unit.
The Fuel Master 21 is a FM21

 

[rickairmedic]

Ok, the new board is in and all of the connections EXCEPT the thermostat wiring.
I want to isolate / eliminate the Fuel Master Board but I see that the new PCB doesn't have the number of connections that the Heat pump and thermostat have. I realize that some of the wires will be doubled up on the terminal block, but it doesn't look like there is a Reversing Valve wire on the PCB. Is this done in the thermostat ?

Model of the furnace is a 8OUHG five ton Heat pump with nat gas piggyback furnace.
The thermostat is a Lenox 21J7201 There are 6 wires in the cable running from the T-stat to the airhandler unit.
The Fuel Master 21 is a FM21

CaptNemo the reversing valve wire should be orange and gets tied together at the furnace one orange from the stat and one from the heat pump on the PCb itself you should have red ( 24volts hot ) white ( heat) green ( fan ) yellow ( AC ) and Blue or black ( 24 volts neutral ) hope this helps if not let me know and I will pull up a schematic on your units.

Rick

 

[CaptNemo]

I got it up and temporarily working yesterday, it looks like the PCB in the outdoor unit wnt kaput as well. I had to run the coil on the reversing valve off of the 24 volt terminals on the contactor, but it's working now. I'll need to order the outside PCB this next week, I wanted to be sure I didn't need the FM21 before I ordered the PCB to get them both at the same time to save on shipping.

 

[CaptNemo]

A big Thank You to Rickairmedic for helping me out on this.

 

[rickairmedic]

A big Thank You to Rickairmedic for helping me out on this.

No Problemo there Capt just hope I can help out Luke as well I feel a need to chew some tail end and I think his dealer might just get to hear me chewin .


Rick

 

[thehotrod11]

Problem with FuelMaster 21 Heatpump module

I know this thread is old, but I found it through Google, and I have the exact same setup in Kansas City. I wanted to upgrade my thermostat so bought a digital one for heat pumps. After hooking it up, my heat pump would not run, so I put my lennox thermo back and it still will not run. Only the nat. gas furnace runs.

When I tilt the thermo so the only the first mercury switch (for the heat pump) is tripped, the nat gas furnace automatically engages. I checked the voltages. At thermo, there was power to R (power), Y1 (1st stage heat), and W1 (2nd Stage heat), no power at O (reversing valve) or E (emergency heat). The same voltages were found on the input side of the FM21 module. But there was no voltage found on the Heatpump/output side of the FM21. Only voltage going to furnace.

So I pulled the W1 wire from the FM21 to see if the thermostat or thermostat wire had a short. I moved thermostat to engage only the 1st stage heating. Checked voltage at Thermostat and power only at R, and Y1. Voltage at input side of FM21 was still R, Y1, and W1.

I flipped the emergency heat switch and it appeared to operate correctly.

So it appears something in the FM21 is causing or forcing the secondary heat routine to run no matter what. What can I check now? I couldn't find any fuses that might have blown. It's been in the 50s around here, so I'm fairly confident the heat pump should be running. I hope someone can offer some good troubleshooting advice for me. Thanks in advance.

 

[mhoffm911]

Rickairmedic is still a frequent visitor to these forums, so he will probably chime in soon. You may be able to find his contact information from other posts or PM him.