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I have a Rheem RHPL-HM2421JC air handler, a Rheem 1.5 ton heat pump condensing unit, and a comfort control thermostat.
The heat and fan worked well over winter. I can also turn the fan mode to "on" and the fan will run. However, if the system is in cool mode and the fan is set to 'auto', nothing happens. I swapped out the circuit board, but the same problem persist. All the wires in the thermostat seem connected, so i am at a lost for the cause. Any suggestions?
Usually A/C, heat, and fan run the blower at different speeds. It's possible that the speed the A/C uses is dead.
Any easy test, is to swap the motor speed wires connected to HEAT and COOL on the board. Then see if the blower starts with the A/C. If it does, that means the speed used by A/C is dead. Depending on the system, you might have to replace the blower, or simply run it at a different speed for A/C.
WARNING: Don't run the A/C with the wrong blower speed for long, as it could damage the system.
If it's an ECM motor, there may not be a way to select/change the speed manually. Or the speed selection might be adjustable using dip switches, or jumpers.
