In an Add-On Heat Pump application, the YorkGuard VI module uses its Outdoor Ambient Sensor and a field-installed Bonnet Sensor (mounted between the furnace & indoor coil) to control "Fossil Fuel" operation.

Qty	Possible Causes:
1	Gas Furnace not Operating
	YorkGuard Mis-Configured or Mis-Wired
	Thermostat Mis-Configured
	2-Stage Furnace not Running 2nd Stage
	Bad Ambient Sensor
	Gas Furnace Under-Sized

CHECKOUT:

1. YorkGuard VI - "Fossil Fuel" Sequence of Operation

For Fossil Fuel Operation, the following setting must be made on the YorkGuard:

FFUEL = Set to "On"
BP = Set for 45, 40 or 35 deg.
LTCO = Set for 20, 15 or 10 deg.
Bonnet Sensor installed & wired to "BS" and "BSG"

2. Outdoor ABOVE Balance Point (BP)

On a call for "Y1" the YorkGuard energizes the compressor for 1st Stage heating.
On a call for "Y2" the YorkGuard energizes the compressor unloading solenoid to put the compressor in full operation.
- The YorkGuard also energizes "Y2 Out" to tell the variable speed indoor fan to go to "High Heat" speed.
On a call for "W" (or "Aux") the YorkGuard will keep Aux Heat outputs "W1 Out" and "W2 Out" de-energized.
- If the heat pump goes into a Lockout condition, the YorkGuard will automatically energize "W1 Out" to satisfy heating demand.

3. Outdoor BELOW Balance Point (BP)

On a call for "Y1" the YorkGuard energizes the compressor for 1st Stage heating.
On a call for "Y2" the YorkGuard energizes the compressor unloading solenoid to put the compressor in full operation.
- The YorkGuard also energizes "Y2 Out" to tell the variable speed indoor fan to go to "High Heat" speed.
On a call for "W" (or "Aux") the YorkGuard will energize "W1 Out" to start the furnace while keeping the compressor operating.
- The compressor continues to operate until the Bonnet Sensor temperature reaches 90 deg.
  - If the furnace fails to operate the heat pump will continue to operate to try to maintain heating.

4. Outdoor BELOW LTCO

The YorkGuard basically enters Emergency Heat mode.
On a call for "Y1" the YorkGuard keeps the compressor off and energizes "W1 Out" to start the gas furnace.