Carrier 60 Service Manual download pdf (Page 25)

2-4

T--295

The unloaders are used to control suction pressure and

thereby prevent coil frosting:

1 C ompressor UnloaderUV1 Relay.

When the suction

pressure decreases below 26 psig (1.77 bar), unload-

er UV1 is energized unloading a cylinder bank (two

cylinders); this output will remain energized until

the pressure increases to above 34 psig (2.31 bar).

2 C ompressor Unloader UV2 Relay.

When suction

pressure decreases below 23 psig (1.56 bar) [on a

GR60], unloader UV2 is energized unloading the

second compressor cylinder bank; this output will

remain energized until the pressure increases to

above 31 psig (2.11 bar).

c. Discharge Pressure

Discharge pressure is also controlled by the unloaders:

1 C ompressor Unloader UV1 Relay.

When the dis-

charge pressure increases above 275 psig (18.71

bar), unloader UV1 is energized; this output will re-

main energized until the pressure decreases below

220 psig (14.97 bar). Staging is ignored during dis-

charge pressure override.

2 C ompressor Unloader UV2 Relay.

When the dis-

charge pressure increases above 285 psig (19.39

bar),unloader UV2 is energized; t his output will re-

main energized until the pressure decreases below

225 psig(15.31 bar).

2.3.8 Evaporator Fan Speed Selection

Temperat ure control is the primary method of

determining the fan speed selection. The following

table indicat es relay operational status for the various

fan motor states while Figure 2-1 provides LogicBoard

speed selections at various deviations form set point..

Table 2 -1. Evaporator Fan Speed Relay Operation

STATE

HIGH

SPEED

RELAYS

EVAP FAN

RELAY

Of f Off Of f

Low Of f On

High On On

2.3.9 Condenser Fan Control

The condenser fans are energized when the compressor

clutch output is energized. The fans are started in low

speed and will remain in low speed until the discharge

pressure increases to 225 psig (15.31 bar). The fans will

remain in high speed until discharge pressure decreases

below 190 psig (12.93 bar). The fans will also be

activated if a high pressure alarm has been activated and

operation has not been locked out (refer to Table 3-3).

2.3.10 Compressor Clutch Control

A belt driven electric clutch is employed to transmit

engine power to the air conditioning compressor.

De-energizing the clutch electric coil disengages the

clutch and removes power from the compressor. The

clutch will be engaged when in cooling and disengaged

whenthesystem isoff,in heatingorduring high andlow

pressure conditions.

The clutch coil is prevented from engagement when the

ambient t emperature is below 45F (7.2C).

The clutch coil will be de-energized if the discharge

pressure rises to the 300 psig (20.41 bar) cutout setting

of the compressor mounted high pressure switch. The

clutch coil will energize when the discharge pressure

falls to 200 psig (13.61 bar).

The clutch coil will be de-energized if the suction

pressure decreases below 10 psig (0.68 bar).

2.3.11 Alarm Description

Alarm descriptions and troubleshooting procedures are

provided i n section 3.

2.3.12 Hour Meters

Hour meterreadings are available in the parameter code

list of the Micromate. The hour meters record the

compressor run time and the total time the evaporator

fans are on. The maximum hours is 999,999. Refer to

paragraph 2.4.3 for instructions on reading parameter

codes.

2.4 MICROPROCESSOR DIAGNOSTICS

The Micromate allows the user to interface with the

microprocessor based control. This allows system

parameters, alarms and settings to be viewed and

modified. On systems with OEM supplied operating

switches, a Micromate may be connected as a service

tool using a special harness. The following instructions

supplement those provided in paragraph 2.1.2. Once a

Micromate is connected as a service tool, the following

instructions are applicable.

2.4.1 Connecting

Connect the Micromate harness to the service port

locatedin thereturnairsectionofthe A/C system.When

the Micromate is connect ed, the panel lights will be

energized and the currently stored setpoint will be

displayed. If any alarm is active, the reading will be

A##, where A indicates that the alarm is active and ##

indicates the alarm number.

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Carrier 60 Service Manual Page 25

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