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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Lennox LZP-4 control panel, I changes a thermostat and now

Customer Question

Lennox LZP-4 control panel, I changes a thermostat and now the control panel is not powering the new or the old thermostat, completely dark. There control panel still working in other part of the house and is controlling the second unit fine. Green displaying on control panel power, but one red led is glowing when cover is removed by the "B" terminal, any thoughts as to what might have gone wrong? Thankyou
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Expert:  gotoman for ac replied 1 year ago.

Attach picture of the wiring at thermostat. Russ

Customer: replied 1 year ago.
Here you go. I tried to move the brown wire in differs open slots after the system would not turn on.
Expert:  gotoman for ac replied 1 year ago.

Do you have picture of old thermostat terminal board. Russ

Customer: replied 1 year ago.
The pictures are of the old thermostat.
Expert:  gotoman for ac replied 1 year ago.

Just sounds like a blown fuse in air handler. There may be a small breaker on transformer in air handler. Turn off power before checking fuse.Open panel of air handler and check the fuse in the low voltage line. If you have a voltmeter check the voltage between R and any terminals to see if you re getting voltage. The board may be powered externally from thermostat. The fuse is in the line from transformer. The transformer is a square component that has high voltage wires on one side and low voltage on the other side. It is labeled 24 volts one side. Russ