Operational Check Out
After the system has been charged and has operated for at least two hours at normal operating conditions without any indication of malfunction, it should be allowed to operate overnight on automatic controls. Then a thorough recheck 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.
c)Observe oil level in compressor crankcase sight glass. Add oil as necessary to bring level to bottom 1/4 of the sight glass.
d)Thermostatic expansion valves must be checked for proper superheat settings. Feeler bulbs must be in positive contact with the suction line and should be insulated. Valves set at high superheat will lower refrigeration capacity. Low superheat promotes liquid slugging and compressor bearing washout.
e)Using suitable instruments, carefully check line voltage and amperage at the compressor terminals. 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 three phase motor compressors, check to see that a balanced load is drawn
by each phase.
f)The maximum approved settings for high pressure controls on our air cooled condensing equipment is 425 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. Recheck all safety and operating controls for proper operation and adjust if necessary.
g)Check defrost controls for initiation and termination settings, and length of defrost period. Set fail safe at length of defrost + 25%.
Example: | 20 minute defrost + 5 minutes |
=25 minute fail safe
h)Check drain pan for proper drainage.
i)Check winter head pressure controls for pressure setting.
j)Check crankcase heater operation if used.
k)Install instruction card and control system diagram for use of building manager or owner.
System Balancing - Compressor Superheat
IMPORTANT:
In order to obtain the maximum capacity from a system, and to ensure
This is extremely important with any refrigeration system. The critical value which must be checked is suction superheat. Suction superheat should be checked at the compressor as follows:
1.Measure the suction pressure at the suction service valve of the compressor and determine the saturation temperature corresponding to this pressure from a
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.
Too high a suction superheat will result in excessive discharge temperatures which cause 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 20˚F at the compressor. We recommend that the superheat at the compressor be between 20˚F and 30˚F.
If adjustments to the suction superheat need to be made, the expansion valve at the evaporator should be adjusted.
NOTE:
All adjustable controls and valves must be field adjusted to meet desired operation. There are no factory preset controls or valve adjustments. This includes low pressure, high pressure, adjustable head pressure systems and expansion valves.
Table 9. Recommended Low Pressure Control Settings for Outdoor Air Cooled Condensing Units
*Minimum |
|
|
| |||
Temp. ˚F |
|
|
| |||
50 | 70 |
| 20 | 90 |
| 35 |
40 | 55 |
| 20 | 70 |
| 35 |
30 | 40 |
| 20 | 55 |
| 35 |
10 | 30 |
| 10 | 45 |
| 25 |
0 | 15 |
| 0 | 25 |
| 7 |
15 |
| 0 | 20 |
| 1 | |
10 |
| 0 | 12 |
| 1 | |
6 |
| 0 | 8 |
| 1"Hg. | |
*Minimum ambient or box temperature anticipated, high pressure control setting:
*The standard preset low pressure switch used for pumpdown is set for 15 PSI cut in / 4 PSI cut out and is a good setting for most pumpdown systems
*ZB Scroll compressors should be set for 25 PSI cut in / 17 PSI cut out
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