44
FORM 145.18-IOM2
ISSUE DATE: 06/17/2020
SECTION 2 - OPERATION
If a low pressure limit switch opens three times within
1 hour of operation, the microprocessor control board
locks out the compressor (a hard lockout) and flashes a
).
Freeze-Stat
If a freeze-stat opens, the microprocessor control de-
energizes the compressor and initiates the ASCD. If
a call for cooling or heating is still present after the
ASCD, the microprocessor control re-energizes the
halted compressor.
Condensate Overflow Switch
A condensate overflow fault occurs if the condensate
overflow switch opens continuously for 30 seconds.
The compressor shuts down regardless of the mini-
mum runtime, and alarm 15 sets. The fan continues
operating in its current state.
The microprocessor control logs the first incident per
compressor request. Lockout occurs on the second fault
occurrence within a request cycle, requiring reset or
power cycling. If the compressor request is removed,
the fault occurrence counter resets to zero. When lock-
outs are removed, the alarm resets.
Safety Controls
The microprocessor control monitors the following in-
puts:
1. A suction line freeze-stat to protect against low
leaving water temperatures (LWTs) (opens at
37.0°F and resets at 49.0°F).
2. A high pressure limit switch to protect against ex-
cessive discharge pressures (opens at 625 psig ±
25 psig).
3. A low pressure limit switch to protect against loss
of refrigerant charge (opens at 38 psig ± 5 psig).
4.
A condensate overflow switch to protect against
condensate overflow.
Coaxial Freeze Protection Setpoint
The field can select the coaxial freeze protection
setpoint. The unit uses a suction line freeze-stat factory
setpoint for compressor lockout when the LWT drops
below 37.0°F (resets at 49.0°F). To lower the setpoint
for low temperature heating applications with an ad-
equate water-antifreeze solution, unplug the freeze-
stat sensor located at P6 on the microprocessor control
board, and plug in the (pink) jumper attached to the
existing harness.
Installing the jumper bypasses the freeze-stat, enabling
heating operation with a leaving glycol fluid mixture
temperature below 35.0°F. Use the jumper only in gly-
col mixture applications with adequate antifreeze pro-
tection. Otherwise, damage can occur. The minimum
loop temperature for cooling is 30.0°F and 20.0°F for
heating.
Random Start
The random start function upon power up imposes
time delay of 4 minutes plus a random delay of 1–64
seconds. A combination of the following determine the
random number generator seed:
•
A fixed seed programmed at the factory
• The serial number
• The model number
• The hours of the unit's compressor runtime
