Troubleshooting guide

Page 8 of 28 / OM 931-3
Control Outputs {A and IV/PR (H8)}
The control outputs are Alarm Fault (A) and Isolation Valve
/ Pump Request {IV/PR (H8)}. The operation of the control
outputs during occupied mode is as follows:
• Alarm Fault (A): energized (no fault).
• Isolation Valve / Pump Request {IV/PR (H8)}: is
selectable to be energized when the compressor is off
(normally closed), or when the compressor is on (normally
open), by moving the wire lead to the appropriate
terminal.
Figure 3: H8 Terminals on MicroTech III Board
Fan Operation
The G terminal controls continuous fan operation. The fan
runs continuously when the G terminal is energized. When the
G terminal is de-energized, the fan cycles with the compressor.
Cooling Mode
The Y1 terminal controls the Cooling Mode of operation.
When the Y1 terminal is energized (24VAC), the following
occurs:
1. The fan energizes.
2. The IV/PR (H8) control output de-energizes or energizes
depending on the H8 terminal wiring (refer to Table 1 on
page 4 & Figure 1 on page 5).
3. The compressor energizes after 30 seconds.
4. If the reversing valve output is energized, the reversing
valve out put will be de-energize within 5 to 20 seconds
of the compressor being energized, depending on the
conguration of jumpers JP7 and JP8.
When the Y1 terminal is de-energized, the following occurs:
1. The compressor de-energizes.
2. The fan de-energizes, unless the G terminal is energized
(24VAC).
3. The IV/PR (H8) control output energizes or deenergizes
depending on the H8 terminal wiring (refer to Table 1 on
page 4 & Figure 1 on page 5).
4. The reversing valve output remains de-energized.
Note: To prevent compressor cycling, the required minimum
on/off time default is 180 seconds. This may cause
the compressor time delay to be longer than indicated
above.
Heating Mode
The W1 terminal controls the occupied Heating Mode of
operation. When the W1 terminal is energized, the following
occurs:
1. The fan energizes
2. The IV/PR (H8) control output de-energizes or energizes
depending on the H8 terminal wiring (refer to Table 1 on
page 4 & Figure 1 on page 5).
3. The compressor energizes after 30 seconds.
4. If the reversing valve output is de-energized, the reversing
valve output will be energize within 5 to 20 seconds
of the compressor being energized, depending on the
conguration of jumpers JP7 and JP8.
When the W1 terminal is de-energized, the following occurs:
1. The compressor de-energizes.
2.The fan de-energizes, unless the G terminal is energized.
3. The IV/PR (H8) control output energizes or deenergizes
depending on H8 terminal wiring (refer to Table 1 on page
4 & Figure 1 on page 5).
4. The reversing valve output remains energized.
Note: To prevent compressor cycling, the required minimum
on/off time default is 180 seconds. This may cause
the compressor time delay to be longer than indicated
above.
Unoccupied Operation – Stand Alone
Thermostat Control
The board will be in unoccupied mode if the unoccupied
terminal (U) is grounded.
Board LED Status – Unoccupied
Y
ellow
Green
Red
On
On
Of
f
Thermostat Inputs (G, Y1, Y2, W1, and W2)
The only thermostat input used during unoccupied operation
is W2, which when energized will activate Heating Mode.
Inputs G, Y1, Y2 and W1 have no effect during unoccupied
mode.
Figure 4: Terminal "U" - Grounded for Unoccupied