Capacity Control Pressure Fig, Condenser Maintenance

CONTROL

SET POINT

ADJUSTMENT

NUT

POWER

HEAD

PRESSURE

DIFFERENTIAL

ADJUSTMENT

SCREW

VALVE BODY

BYPASS

PISTON RING

BYPASS PISTON-USED
WITH HOT GAS BYPASS	DIFFERENTIAL SCREW
TYPE OF UNLOADING ONLY.	DIFFERENTIAL SCREW
NOT REQUIRED WITH	SEALING CAP (CAP MUST
SUCTION CUTOFF TYPE	BE REPLACED TO PREVENT
UNLOADING.	REFRIGERANT LEAKAGE)

Fig. 7 — Capacity Control Valve

(Pressure Type)

Table 4 — Capacity Control Reduction Steps

			% Full Load Capacity
	NO. OF	100		67	49	32
UNIT 06D,07D	CONTR			% Full Load kW
	CYL	100		73	57	46
		100		73	57	46
		Number of Active Cylinders
ALL 4 CYLINDER	2	4		—	2	—
MODELS	2	4		—	2	—
MODELS
ALL 6 CYLINDER	4	6		4	—	2
MODELS	4	6		4	—	2
MODELS

Capacity Control Pressure (Fig. 8)

LOADED OPERATION — Pressure-operated control valve is controlled by suction pressure and actuated by discharge pressure. Each valve controls 2 cylinders (one bank). On start-up, controlled cylinders do not load up until differential between suction and discharge pressures is approximately 25 psi.

When suction pressure rises high enough to overcome control set point spring, the diaphragm snaps to the left and relieves pressure against the poppet valve. The drive spring

moves the poppet valve to left and it seats in the closed position.

With poppet valve closed, discharge gas is directed into the unloader-piston chamber and pressure builds up against the piston. When pressure against unloader piston is high enough to overcome the unloader valve spring, piston moves valve to the right, opening suction port. Suction gas can now be drawn into the cylinders and the bank is running fully loaded.

UNLOADED OPERATION — As suction pressure drops below set point, control spring expands, snapping diaphragm to right. This forces poppet valve open and allows gas from discharge manifold to vent through base of control valve to suction side. Loss of full discharge pressure against unloaded piston allows unloader valve spring to move valve left to closed position. The suction port is blocked, isolating the cylinder bank from the suction manifold. The cylinder bank is now unloaded.

CONDENSER MAINTENANCE

To inspect and clean condenser, drain water and remove condenser heads. To drain condenser, shut off water supply and disconnect inlet and outlet piping. Remove drain plugs and vent plug.

With condenser heads removed, inspect tubes for refrigerant leaks. (Refer to Carrier Refrigerant Service Techniques Manual.)

Clean condenser tubes with nylon brush (available from Carrier Service Department). Flush water through tubes while cleaning. If hard scale has formed, clean tubes chemically. Do not use brushes that will scrape or scratch tubes.

Because the condenser water circuit is usually an open system, the condenser tubes may be subject to contamination by foreign matter. Local water conditions may cause excessive fouling or pitting of tubes. Condenser tubes, therefore, should be cleaned at least once a year or more often if the water is contaminated.

Proper water treatment can minimize tube fouling and pitting. If such conditions are anticipated, water treatment analysis is recommended. Refer to the Carrier System Design Manual, Part 5, for general water conditioning information.

If hard scale has formed, clean the tubes chemically. Con- sult an experienced and reliable water-treatment firm in your area for treatment recommendations. Clean the condenser by gravity or by forced circulation as shown in Fig. 9 and 10.

IMPORTANT: If the ambient temperature is below 32 F during a shutdown period; protect the condenser from freezing by draining the water from the system or by add- ing antifreeze to the water.