heatcraft-refrigeration-p h-im-fl1a User Manual

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  

 

 

“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.
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. Heatcraft Refrigeration Products 

recommends that the superheat at the compressor be 

between 30˚F and 45˚F.
If adjustments to the suction superheat need to be made,  

the expansion valve at the evaporator should be adjusted.

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)  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. 

 

(d)  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.  

 

(e)  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.   

 

 

Recheck all safety and operating controls for proper    

 

 

operation and adjust if necessary.  

 

(f)  Check winter head pressure controls for pressure  

 

 

setting.

 

(g)  Check crankcase heater operation if used. 

 

(h)  Install instruction card and control system diagram for   

 

 

use of building manager or owner.