CeilAir CW series Betreibershandbuch PDF herunterladen (Seite 32)

(©July, 2008)

CeilAiR OHS Series Installation, Operation & Maintenance Manual

ir Technology Systems, Inc.

2-21

CAUTION

POE oil is used in systems with R407C refrigerant.

POE oil quickly absorbs moisture when exposed to

air. High POE oil moisture levels react with refrigerant

to form acid, which results in system contamination.

Keep entire system sealed as much as possible and

minimize exposure of POE oil to outside air.

Familiarize yourself with the charging procedures

discussed in section 2.8.1 of this manual. Instead of

adding R22 vapor to the suction port as described

under “Preparing System for Charging”, the initial

charge will be performed by introducing R407C liquid

to the discharge side of the compressor. (See below)

PREPARING SYSTEM FOR CHARGING

1. With all the system piping connections made,

perform a dry nitrogen leak detection test on the

system. Using dry nitrogen only, pressurize the

system to 150 psig. Since there is no refrigerant

in the system to detect, leaks may be detected

by observing the standing pressure.

2. After ensuring there are no leaks, evacuate the

system to 50 microns and hold the vacuum for 2

hours.

3. Break the vacuum by supplying R407C liquid to

the discharge port near the compressor until the

pressure is raised to about 50 psig. This small

holding charge allows the low pressure switch to

“make” through the process of fine tuning the

system charge.

FINE TUNING THE SYSTEM CHARGE

4. Disconnect the refrigerant cylinder from the

discharge side of the compressor and connect it

to the suction side.

5. Start the system and use the microprocessor

controller to lower the temperature setpoint 3-5°F

below room temperature, ensuring cooling

remains on as the unit is charged.

6. Allow the discharge pressure to rise to 225-280

psig and hold it constant. On cool days it may be

necessary to restrict the airflow across the

condenser (or reduce the water glycol flow), to

raise the pressure.

7. Slowly meter R407C liquid refrigerant through the

suction side while watching for the sight glass to

clear of bubbles.

CAUTION

Add liquid refrigerant slowly to prevent the refrigerant

oil from “washing out” of the compressor.

8. Take a superheat reading near the feeler bulb from

the thermal expansion valve, ensuring the tem-

perature-measuring device is well insulated. The

ideal superheat temperature is 12-15°F. The

maximum allowable superheat temperature is

20°F.

9. While monitoring the sight glass, take a sub-

cooling temperature reading on the output side of

the condenser. The sub-cooling temperature

should be 10-20°F.

10. If necessary, add liquid refrigerant to maintain

adequate sub-cooling temperature.

2.8.2.1 Flooded Head Pressure Control Systems

In units with R407C refrigerant using flooded head

pressure control, a receiver is provided to store the

refrigerant during the time the condenser is not using

the extra refrigerant charge. Once a clear sight glass

has been achieved, additional refrigerant must be

added to the receiver.

A level indicator is located on the side of the receiver

to assist the service technician in charging the air

conditioning system. The proper charge can be

determined by viewing the position of the “float ball”

while the unit is running. If the “float ball” is positioned

at the bottom of the sight indicator, additional refriger-

ant charge is needed. When the “float ball” reaches

the top of the indicator, the unit is fully charged.

2.9 System Settings and Adjustments

2.9.1 Low/High Pressure Limit Switch

Air conditioning systems utilizing thermal expansion

valves are equipped with hermetically sealed high-

pressure and low-pressure switches. These switches

are pre-set by the manufacturer and cannot be ad-

justed. The high-pressure switch opens at 410 psig and

has a manual reset. The low-pressure switch opens at

10 psig (± 4) and closes at 32 psig (± 5) and has an

automatic reset.

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