I have a PTAC unit in the room above my garage (Amana PTH123A35AC) that I’m trying to connect a thermostat (Honeywell 50018270-001) to. These are my current connections:

PTAC Thermostat
B B
C C
GL G
R R
W2 W
Y/W1 Y
GH Unused
Unused O
Unused Rc

The only thing that’s not working is the cool setting. Heat and the fan are working fine. I have tried connecting R to Rc and B to O, but neither worked. I’m fairly certain I have something incorrectly wired here, but I’m just not sure which connection.

PTAC Serial Number Decoded:

  • PTH: Standard Heat Pump PTHP
  • 12: 12,000 BTU/h, 60Hz
  • 3: 230/208V, 60Hz, 1 Phase
  • A: First Design Series
  • 35: 3.5 kW (230/208V)
  • AC: Standard Model

Does anyone have any ideas as to why the cool setting isn’t working?