Form CP-MAPS-D12 with FX05, Page 10
Heating and
Cooling Control
Modes (cont’d)
Cooling Mode
(cont’d)
Cooling Staging
Upon a call for mechanical cooling to maintain the active discharge air setpoint,
the unit will enable a stage when the discharge air temperature is more than ½
of the cooling proportional band (CPP) above the setpoint. (Default CPP value
is 10ºF.)
Example: Active setpoint = 70ºF. The 1st stage enables when the dis-
charge air temperature is greater than 75ºF. Likewise if the discharge air
temperature is below 65ºF, an active stage of cooling is turned OFF.
The system has intra-stage time delays of 4.5 minutes. Thus, compressors
have a minimum ON and OFF time of 4.5 minutes. After the rst stage has
been turned ON and the discharge air temperature is still 5ºF greater than the
setpoint (½ CPP) and 4.5 minutes has passed, the unit will turn on stage 2
cooling. Because the unit has 33%, 66%, and 100% staging, compressor 1 will
turn OFF and compressor 2 will turn ON.
If after 4.5 minutes the same condition exists, stage 3 will be active and both
compressors 1 and 2 will be ON. If the discharge air temperature value is
between the cooling proportional band (CPP is 65ºF - 75ºF), the active stage
will remain ON. If the dAt falls 5ºF below the setpoint, the staging control will
act in reverse, turning OFF stages.
Cooling Mode Lockout
The unit is equipped with a manual reset high pressure switch and an auto-
reset low pressure switch for each compressor circuit. If any pressure switch
trips, that particular mechanical cooling circuit is disabled. Each circuit on the
evaporator coil has an auto-reset froststat which will disable the cooling circuit
if the temperature drops below 36ºF.
To reduce compressor cycling, the compressors are enabled to run based upon
outdoor dry bulb temperature and enthalpy settings. No mechanical cooling is
allowed to operate if the outside air temperature is below the cooling mode
lockout (oC1). Default oC1 setting is 68ºF; adjustable range is 58 to 130ºF. If
the compressors are enabled and the temperature falls below the oC1 setting,
the minimum run time will keep the compressors ON. ALL compressors will
immediately turn OFF after the current minimum run time expires; the unit does
not stage down.
If the unit is equipped with an outdoor air humidity sensor (Point AI-2), the
compressors are locked out until the outside air enthalpy value rises above the
lockout settings
Stage 1 compressor is locked out when the outdoor air
enthalpy is below EN1 settings.
Stage 2 compressor is locked out when the outdoor air
enthalpy is below EN2 setting.
Stage 3 compressors are locked out when the outdoor air
enthalpy is below EN3 settings.
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