Operation Errors; Safety Controls - Johnson Controls VB09 Installation, Operation And Maintenance Manual

FORM 145.18-IOM1
ISSUE DATE: 8/30/2018
If the unit must be reset more than twice
on consecutive operating cycles, check
the unit for a dirty filter, abnormal EWT,
inadequate or excessive water flow, or
refrigerant circuit malfunction. If the
unit continues to cutout, contact a trained
service technician.

Operation Errors

Each refrigerant system is monitored for operation out-
side of the intended parameters. Errors are handled as
described below. All system errors override minimum
runtimes for compressors.
High Pressure Limit Switch
If a high pressure limit switch opens, the microproces-
sor control de-energizes the compressor, initiates the
ASCD, and stops the unit fans (soft lockout). If a call
for cooling or heating is still present at the conclusion
of the ASCD, the microprocessor control re-energizes
the compressor and unit fan.
If a high pressure limit switch opens three times within
2 hours of operation, the microprocessor control per-
manently locks out the system compressor, requiring a
manual reset of the system (a hard lockout). To manu-
ally reset, either de-energize the 24-volt power to the
unit or turn the room thermostat to OFF, then back to
either HEAT or COOL as required. The microproces-
sor control flashes a fault code indicating the high pres-
sure lockout (see Table 13 on page 42).
Low Pressure Limit Switch
The microprocessor does not monitor the low pressure
limit switch during the initial 30 seconds of compressor
operation. For the following 30 seconds, the micropro-
cessor control monitors the low pressure limit switch
to ensure it closes. If the low pressure limit switch fails
to close after the 30 second monitoring phase, the mi-
croprocessor control de-energizes the compressor, ini-
tiates the ASCD, and stops the fan (a soft lockout).
Once the low pressure limit switch is proven (closes
during the 30 second monitor period), the microproces-
sor control monitors the low pressure limit switch for
any openings. If the low pressure limit switch opens
for more than 5 seconds, the microprocessor control
de-energizes the compressor, initiates the ASCD, and
stops the compressor (a soft lockout).
If the call for cooling is still present after the ASCD,
the microprocessor control re-energizes the compres-
sor.
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
fault code (see Table 13 on page 42).
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
34.0°F and resets at 48.0°F).
2. A high pressure limit switch to protect against ex-
cessive discharge pressures (opens at 600 psig ±
25 psig).
3. A low pressure limit switch to protect against loss
of refrigerant charge (opens at 55 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 35.0°F (resets at 48.0°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.
SECTION 2 - OPERATION
2
41