Safety monitoring
The control monitors the following values:
•
Outdoor, supply, and return air temperatures
•
The high and low pressure switch status on the independent refrigerant circuits
•
The voltage supplied to the unit. If the low voltage is due to a brown out, or some other
electrical issue occurs, the control protects the unit
Low ambient
With a low ambient damper kit or VFD on the condenser installed, an integrated low ambient
control allows units to operate in the cooling mode down to 0.0°F outdoor ambient. Optionally,
when the OAT is low and with the airside economizer option installed, the control board can be
programmed to lock out the compressors.
Anti-short cycle delay (ASCD) protection
To assist compressor life, the standard control incorporates an ACSD. The compressor reliability is
further ensured by programmable minimum runtimes.
Fan delays
Fan on and fan off delays are fully programmable. Furthermore, the heating and cooling fan delay
times are independent of one another. All units are programmed with default values based upon
their cooling or heating capacity configuration.
Nuisance trip protection and three strikes
To prevent nuisance calls, the control board has three soft faults before a hard lock out operation.
The high/low-pressure switch, anti-freeze protection, low voltage, or heating high limit must trip
three times within two hours before the unit control board locks out the associated compressor.
The LCD screen displays an alarm message.
Lead-lag
An integrated lead-lag option is available However, never enable it on DSH units. This option can be
selected on the unit control board. The default factory setup is always disabled.
Note:
Enabling lead-lag function affects logic of DSH unit and disables unit operation.
Condensate overflow switch
A condensate overflow fault occurs when the condensate overflow switch opens for the first time,
as the switch is connected to the onboard shutdown (SD) contact. The compressor is shut down
regardless of minimum runtime. The ASCD is initiated and the alarm is tripped. The fan continues
to operate in its current state. The compressor re-energizes once the condensate overflow switch
closes, the ASCD has been satisfied, and a call for cooling is still present.
Operation
Compressor operation
Compressor operation includes the following features:
1. Compressors are controlled by the Y1 through a maximum of Y4 thermostat inputs.
CAUTION
As lead-lag function must be turned OFF, Y1 input energizes the C1 output when the compressor #1
ACSD is at 0 and all refrigerant safety devices are closed (default 5 minutes).
Model DSH024C–120C Horizontal R-410A Air Conditioning Units C-Generation Smart Equipment Controller
46
Johnson Controls
