Carrier 38APS025 Manual

Also see for 38APD115: Installation instructions

Carrier 38APS025 Manual Manual pdf 67 page image

67As the capacity requirement begins to decrease, the ma-chine controls will reduce the unit’s capacity to maintain theControl Point. If the unit is equipped with Minimum LoadControl, it will not be active until the unit is on its last stage ofcapacity.C.TYP = 3 (TSTAT MULTI) — This configuration willallow the MBB to monitor the thermostat inputs to make adetermination of supply air temperature. Unlike traditional2-stage thermostat control, the unit is allowed to perform VAVstyle operation using multiple stages of cooling capacity toattempt to meet the current Control Point (Run Sta-tusoVIEWoCTPT).Recommended Applications — This control scheme is rec-ommended for constant volume or 100% outdoor air applica-tions. It can be used with or without digital compressors. Thiscontrol method is recommended for 38APD,APS025-030 unitswith digital scroll option and 38APD,APS040-130 units withtwo-stage thermostat control. Minimum Load Control is sup-ported by this control scheme. Minimum Load Control anddigital compressor operation are not supported simultaneously.Hardware Requirements• supply air sensor• return air sensor or mixed air sensor• 2-stage thermostatThis control scheme requires a supply air sensor and a returnair sensor or mixed air sensor. In lieu of wiring sensors to the38AP unit, both values can be communicated via CCN to the38AP. For information on broadcasting values, see the sectionThermistors on page 28. ConfigurationoOPT1oRAT.T(RAT Thermistor Type) and ConfigurationoOPT1oSAT.T(SAT Thermistor Type) must be configured for either 0 (5 k:)or 1 (10 k:) type sensors whether they are hard wired or theirvalues are communicated to the controller.Required Configurations — Table 27 lists the configurationsrequired for proper operation.Recommended Settings — With this Control Type, CSP.2should be set to the design Supply Air Temperature. CSP.1will depend on the application. The difference between thedefault values for CSP.1 and CSP.2 is 5° F (2.8° C). In mostcases, the default differential is acceptable, but the applicationmay require a smaller or larger difference. For example, a facesplit coil may a larger differential. CSP.1 should be set to avalue that allows the unit to operate without rapid cycling.CSP.1 should be greater than CSP.2 to allow the unit toproduce a lower supply air temperature when Y2 is made, ifthe unit has the available capacity.Wiring— See Fig. 81.Sequence of Operation — The MBB monitors the thermostatinputs to make a determination of Active Set Point (Run Sta-tusoVIEWoSETP). The control will vary the Active SetPoint based on Y1 and Y2 inputs. When Y1 is closed CoolingSetpoint 1 (SetpointsoCOOLoCSP.1) will be used and whenY2 is closed Cooling Setpoint 2 (SetpointsoCOOLoCSP.2)will be used as the basis for the Active Set Point, SETP. Ther-mostat inputs can be monitored at the unit’s interface device,Y1Thermostat Input (InputsoGEN.IoY.1) and Y2 Thermo-stat Input (InputsoGEN.IoY.2). With this type of control,the MBB capacity control routine stages compressor capacityto attempt to meet the current Control Point (Run Sta-tusoVIEWoCTPT). The Control Point (Run Sta-tusoVIEWoCTPT) is the Active Set Point (SETP) adjustedfor any temperature reset that is applied. See TemperatureReset on page 129 for additional information.For mechanical cooling, the unit’s Control Method (Con-figurationoOPT2oCTRL) and inputs must allow the ma-chine to run. See Control Methods on page 60 for additionalinformation.Table 27 — C.TYP=3 (Tstat Multi) Required ConfigurationCONFIGURATION MODESUBMODE ITEM DISPLAY ITEM DESCRIPTION COMMENTOPT1RAT.T X RAT Thermistor TypeDefault: 0Range: 0 to 2Must be set for appropriate value:0 = 5 k:1 = 10 k:2 = NoneSAT.T X SAT Thermistor TypeDefault: 0Range: 0-2Must be set for appropriate value:0 = 5 k:1 = 10 k:2 = NoneOPT2 C.TYP X Machine Control Type Default: 4Range: 1 to 9Set Item to 3 (Tstat Multi)SETPOINTS MODECOOLCSP.1 XX.X Cooling Setpoint 1Range: 40.0 to 80.0 F (4.4 to 26.7 C)Default: 60.0 F (15.6 C)Set for desired Supply Air Temperaturewith Y1 input.CSP.2 XX.X Cooling Setpoint 2Range: 40.0 to 80.0 F (4.4 to 26.7 C)Default: 55.0 F (12.8 C)Set for desired Supply Air Temperaturewith Y2 input. Should be lower thanCSP.1