Heatcraft Refrigeration Products Air-Cooled Condensers none User Manual download pdf (Page 8)

Start-Up

Check for proper fan rotation. Air is drawn through the coil on all

units. Be sure the fans turn freely.

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 eld 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 conguration, line sizing,

operating pressures and compressor and component mounting

all contribute to the presence and magnitude of these pulsations.

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 muer be installed in the refrigeration

piping. In all cases, the recommendations of the compressor or

muer manufacturer must be followed when selecting these

components.

Fan Cycling

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 dierence 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.

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 dierential in the control

settings or set points. If ooding valves are used with fan cycling,

they must be set to follow the fan cycling.

Recommended dierential settings for ambient sensing

thermostats are 5° F and a minimum of 35 PSIG dierential for

pressure switches. However, system or climate conditions vary

and the controls may require further eld adjustment to provide

optimum system performance and prevent short cycling.

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 o usually results in rapid, short cycling of the fans and

erratic head pressure control.

If additional head pressure control is necessary beyond letting the

lead fan run, we recommend adding variable speed or ooding

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.

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.

Operation

Winter Operation Head Pressure Control

The capacity of an air-cooled condenser varies with the dierence

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 suciently high to insure proper operation of the

refrigerant expansion valve during low ambient operation, and

also allow sucient capacity so that excessively high condensing

temperatures do not result during high ambient conditions.

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 eect, 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.

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Heatcraft Refrigeration Products Air-Cooled Condensers none User Manual Page 8

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