Operational Checkout; System Balancing - Heatcraft Refrigeration Products II Installation & Operating Instructions Manual

Mccu condensing units

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After the system has been charged and has operated for at least 2 hours at normal operating conditions

without any indication of malfunction, it should be allowed to operate overnight on automatic controls. Then a

thorough re-check of the entire system operation should be made as follows:

(a) Check compressor discharge and suction pressures. If not within system design limits, determine why

and take corrective action.

(b) Check liquid line sight glass and expansion valve operation. If there are indications that more

refrigerant is required, leak test all connections and system components and repair any leaks before

adding refrigerant.

Voltage must be within 10% of that indicated on the condensing unit nameplate. If high or low voltage

is indicated, notify the power company. If amperage draw is excessive, immediately determine the

cause and take corrective action. On 3 phase motor compressors, check to see that a balanced load

is drawn by each phase.

(d) The maximum approved settings for high pressure controls on Heatcraft air cooled condensing

equipment is 400 psig. On air cooled systems, check as follows:

• Disconnect the fan motors or block the condenser inlet air.

• Watch high pressure gauge for cutout point.

• Re-check all safety & operating controls for proper operation and adjust if necessary.

(e) Check head pressure controls for pressure setting.

(f)

Check crankcase heater operation if used.

(g) Install instruction card and control system diagram for use of building manager or owner.

IMPORTANT: In order to obtain the maximum capacity from a system, and to

ensure trouble-free operation, it is essential to balance each and every system.

The critical value to be checked here is suction superheat at the compressor:

1. Measure the suction pressure at the suction service valve of the compressor and determine the saturation

temperature corresponding to this pressure from a "Temperature-Pressure" chart.

2. Measure the suction temperature of the suction line about one foot back from the compressor using an

accurate thermometer.

3. Subtract the saturated temperature from the actual suction line temperature. The difference is superheat.

Too low a suction superheat can result in liquid being returned to the compressor. This will cause dilution of

the oil and eventual failure of the bearings and rings or in the extreme case, valve failure or even "slugging" of

the compressor.

Too high a suction superheat will result in excessive discharge temperatures which causes a break down of

the oil and results in piston ring wear, piston and cylinder wall damage.

It should also be remembered that the system capacity decreases as the suction superheat increases. For

maximum system capacity, suction superheat should be kept as low as is practical. Copeland mandates a

minimum superheat of 20ºF and a maximum of 45ºF at the compressor. Heatcraft recommends a superheat

of 30ºF.

Adjust the superheat by changing the superheat setting on the board to increase or decrease as needed to

obtain desired superheat value at the compressor.