Heatcraft Refrigeration Products none Fan Cycling, Discharge Gas Pulsation

Start-Up

Fan Cycling

Check for proper fan rotation. .Air is drawn through the coil on all units. .Be sure the fans turn freely...

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Rotation of the motors and blades should be in a “CW” direction looking at the unit from the blade side. .On three phase units, it may be necessary to reverse two of the three power leads to the unit..

NOTE:	The manifold assembly is not designed to
	support field piping. Any damages to the
	condenser due to excessive weight,
	pressure or vibration will not be covered
	by our standard warranty.

Discharge Gas Pulsation

Gas pulsations in a refrigeration system are most commonly associated with the compressor and connecting discharge piping. .Variations in the system piping configuration, line sizing, operating pressures and compressor and component mounting all contribute to the presence and magnitude of these pulsations...

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The vibration and movement of components caused by the pulsations may result in line breakage or damage to the condenser. .In order to eliminate discharge pulsations and the potential for related condenser damage, it is recommended that a discharge muffler be installed in the refrigeration piping. .In all cases, the recommendations of the compressor or muffler manufacturer must be followed when selecting these components..

Operation

Winter Operation Head Pressure Control

The capacity of an air-cooled condenser varies with the difference between the entering air dry bulb temperature and the condensing temperature of the refrigerant. .Since air temperature in some regions varies as much as 100° from summer to winter, some means must be employed to keep the condensing temperature sufficiently high to insure proper operation of the refrigerant expansion valve during low ambient operation, and also allow sufficient capacity so that excessively high condensing temperatures do not result during high ambient conditions...

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The low limit of the head pressure is dependent upon the required pressure drop across the thermostatic expansion valve. . For normal air conditioning applications, head pressure should be maintained above a condensing temperature corresponding to 90° F. .This, in effect, corresponds to a normal lower limit of about 60° F ambient air. .Since air conditioning is not normally required at these lower ambient temperatures, condenser head pressure control may not always be necessary. .However for those applications which are of such a nature that operation is required below 60° F ambient air temperature, additional head pressure control will be required..

A decrease in ambient air temperature results in a capacity increase in the air-cooled condenser. .This capacity increase is directly proportional to the temperature difference between the condensing temperature and the temperature of the ambient air entering the condenser. .Since air-cooled condensers are often required to operate over a wide range of ambient air temperatures and variable loading conditions, provisions must be made to maintain the overall system balance. .Any air-cooled condenser tends to run at a low head pressure when operating in

a low ambient air temperature. .Low head pressures could result in poor expansion valve operation and poor system operation...

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The cycling of condenser fans provides an automatic means of maintaining head pressure control, within reasonable limits, at lower ambient air temperatures. .A fan cycling control system allows fans to cycle in sequence by sensing either ambient temperature or condensing pressures. .However, care must be used by the engineer or installing contractor in making adjustments to prevent short cycling of the fan motors. .Short cycling is normally caused by too close a differential in the control settings or set points. .If flooding valves are used with fan cycling, they must be set to follow the fan cycling...

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Recommended differential settings for ambient sensing thermostats are 5° F and a minimum of 35 PSIG differential for pressure switches. .However, system or climate conditions vary and the controls may require further field adjustment to provide optimum system performance and prevent short cycling...

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Any fan cycle that is less than three minutes is considered short cycling, and could be detrimental to the system. .Adjust controls accordingly. .It is also recommended that the fan closest to the header end of the condenser be wired to run continuously, whenever the compressor(s) is (are) operational. .Cycling all of the fans off usually results in rapid, short cycling of the fans and erratic head pressure control...

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If additional head pressure control is necessary beyond letting the lead fan run, we recommend adding variable speed or flooding controls. .If cycling the header fan is necessary for adequate head pressure control, we recommend cycling on pressure. .Ambient sensing thermostats should never be used to cycle the lead fan...

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Fans must not cycle in multiples except on double wide single circuit condensers where they may cycle in pairs (one motor on each side). .Do not cycle more than two fans at a time on double wide condensers and only one fan at a time on single wide condensers..