Carrier 48MA/50ME016-040 Compressor Capacity Control Unloaders, Head Pressure Control, LOW Charge

TO ADD OR REMOVE OIL

1.Close liquid line and hot gas bypass shutoff valves. See Fig. 31.

2.Pump down compressor and close suction and discharge service valves. Recover remaining refrigerant in compressor.

3.Add oil through oil ®ller plug.

4.To remove oil, remove crankcase oil drain plug, and drain only as much oil as is required.

Compressor Capacity Control Unloader(s)

(Fig. 36) Ð Unloader(s) on compressor no. 1 are suction- pressure actuated to load or unload compressor at factory settings indicated in Table 1. If necessary, unloader(s) may be ®eld adjusted or reset as follows:

CONTROL SET POINT (Cylinder Load Point) Ð This un- loader set point is adjustable from 0 to 85 psig. To adjust, turn control set point adjustment nut clockwise to its bottom stop. In this position, load point is 85 psig. Turn adjustment nut counterclockwise to desired load point. Each full turn counterclockwise decreases load point by 7.5 psig.

PRESSURE DIFFERENTIAL (Difference Between Cylin- der Load and Unload Points) Ð This unloader set point is adjustable from 6 to 22 psig. To adjust, remove differential adjustment screw sealing cap to expose pressure differential adjustment screw. Turn adjustment screw counterclockwise to its backstop position. In this position pressure differential is 6 psig. Turn adjustment clockwise to desired pressure dif- ferential. Each full turn clockwise increases differential by 1.5 psig.

Fig. 36 Ð Compressor Capacity Control

Unloader

Crankcase Heater(s) Ð One heater for each compres- sor keeps oil free of refrigerant while compressor is off. Crank- case heater(s) is automatically deenergized when the com- pressor(s) is in operation.

If unit power is shut off for longer than a few hours, make sure power is on and that crankcase heater(s) has been on for at least 24 hours prior to start-up. This will ensure that re- frigerant has been driven out of compressor crankcase(s). To prevent start-up during this warm-up period, set control cir- cuit service switch at OFF position.

Refrigerant Charge Ð Quantity and type of refriger- ant is shown on unit nameplate and in Table 1. Add refrig- erant as follows:

NO CHARGE Ð Evacuate refrigerant system and add re- frigerant quantity speci®ed or add 15 lb of refrigerant vapor to system and then refer to Low Charge section below.

LOW CHARGE

1.Set control circuit service switch at OFF position.

2.Disconnect evaporator-fan contactor.

3.Manually close air¯ow switch (AFS1) on evaporator fan housing (Fig. 34 and 35) with a piece of tape.

4.Remove MH jumper (or master heating relay, MHR, if remote control panel accessory is used) from zone con- trol board to lock out heating.

5.Remove all cooling relays (CR) except CR8, from zone control board.

6.Add jumper on terminals R-Y on module 8.

7.Reset control circuit service switch to ON position.

8.Operate unit for about 5 minutes.

9.Add refrigerant vapor at no. 1 compressor suction serv- ice valve ®tting at a rate of one lb per minute.

10.Check liquid level in accumulator sight glass. Use ac- cumulator no. 1 on 040 units (adjacent to compressor no. 1). Add refrigerant until sight glass is 1¤2 full. If sight glass appears clear (no bubbles) but a ®lm of refrigerant shows at bottom of sight glass, refrigerant level is be- low sight glass. Continue adding refrigerant until sight glass is 1¤2 full. If sight glass appears clear, but bubbles can be seen, refrigerant level is above top of glass. Re- frigerant system is overcharged. Recover refrigerant un- til sight glass is 1¤2 full.

11.When correct refrigerant charge has been achieved, re- store unit to normal operation (reverse Steps 2-7).

12.Be sure air¯ow switch (AFS1) functions normally and control circuit service is set at ON position.

Head Pressure Control

MOTORMASTER HEAD PRESSURE CONTROL DEVICE Ð Outdoor (condenser) fan motor no. 1 (OFM1) is a 208/230-v motor operated by a Motormaster device ther- mistor (a thermally sensitive resistor) located on the con- denser coil as shown in Fig. 37. The function of this control is to maintain proper saturated condensing temperature at low outdoor ambient temperatures. The control does this by modulating OFM1 speed in response to the saturated con- densing temperature sensed by the thermistor. Control is fac- tory set and cannot be adjusted or serviced. However, ther- mistor or control may be replaced if necessary.

FAN CYCLING PRESSURESTAT Ð Outdoor (condenser) fan motor no. 2 (OFM2), and no. 3 on 3-fan units (OFM3) is controlled by a nonadjustable pressurestat connected to compressor no. 1.

Fan(s) shuts off at 86 F saturated condensing temperature (160 psig), restarts at 118 F (approximately 255 psig).

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