Daikin IM 830-6, Installation And Maintenance Manual

www.DaikinApplied.com 41 

IM 830-6

Split Systems Guidelines

The following provides basic guidelines that will provide proper 

system cooling and operation of an R-410A commercial DX/hot 

water system for school applications. DX system components 

must be matched and sized correctly (not oversized) for the load.
The DX system 

must

 incorporate the following, provided by 

others, for proper operation:
• 

Size piping per ASHRAE Refrigeration Handbook (correct 

refrigerant and compressor oil flow), see 

Table 36 on page 42

.

• 

Use clean sealed refrigerant grade piping (prevent system 

contamination)

• 

Install Liquid Line Filter Dryer (clean/dry system to prevent 

damage of operating components), see 

Figure 77 on page 42

.

• 

Install Liquid Line Sight Glass (indicates refrigerant 

dryness and if liquid in liquid line - do not use the sight 

glass to determine when refrigerant system is charged 

correctly), see 

Figure 77 on page 42

.

• 

Install pressure taps on the unit ventilator's liquid line and 

suction lines for subcooling and superheat measurements 

at the unit ventilator, see 

Figure 77 on page 42

.

• 

Install High Pressure Switch at condensing unit wired 

in condenser control system (protects compressor and 

refrigerant system from excessive pressures - condenser 

fan failure or overcharging), see 

Figure 78 on page 42

.

• 

Install Low Pressure Switch at condensing unit wired in 

the condenser control system (low refrigerant pressure 

switch protects the system under low refrigerant suction 

conditions), see 

Figure 78 on page 42

.

• 

Install Low Ambient Temperature Switch at condensing 

unit wired in the condenser control system (locks out 

mechanical cooling below 60°F - proper system operation 

and free economizer usage), see 

Figure 78 on page 42

.

Figure 75: Typical Piping and Wiring for Split System

• 

Incorporate Compressor Time Delay (5 minute) in 

condensing unit control system (reduces excessive 

compressor cycling), see 

Figure 78 on page 42

.

• 

Single phase compressors - consider hard start kits to 

overcome non-equalized pressure in refrigerant lines.

• 

Incorporate Low Refrigerant Temperature Sensor (T4) in 

condensing unit control system (T4 protects the system 

under low refrigerant suction conditions) see 

Figure 78 on 

page 42

.

• 

 UV fans must continue to run upon Low Refrigerant 

Temperature trip of T4 (controls by others) or ICT 

(MicroTech) (evaporator air flow dissipates residual low 

coil surface temperatures - suction pressures raised, coil 

frosting reduced), see 

Figure 78 on page 42

.

• 

UV fans must continue to run for set time period during 

unoccupied mode after satisfaction of the space 

sensor (dissipates residual low evaporator coil surface 

temperatures - reducing coil frosting).

• 

Lock the Face and Bypass Damper (actuator spring return 

to full face when de-energized) in the full face position during 

mechanical cooling (full air through evaporator coil reduces 

low refrigerant suction conditions, potential coil frosting)

• 

When Brazing bleed Nitrogen through piping (reduced 

oxides and blockage in piping/TXV)

• 

Use Heat Sink when brazing to prevent overheating the 

TXV valve body and bulb (avoid valve damage and erratic 

operation).

• 

Verify the TXV bulb securely attached at 2 or 10 o’clock 

for 7/8" and smaller diameter suction line piping (proper 

suction gas sensing and reduced hunting) See 

Figure 74 

on page 40

.

• 

Insulate the TXV bulb (reacts to refrigerant temperatures 

and not ambient), see 

Figure 76 on page 42

.

• 

Insulate the suction line piping (minimum heat pickup), see 

Figure 75

 & 

Figure 76

.

• 

Evacuate and properly charge the refrigerant system, see 

Figure 77 on page 42

.

• 

Charge to subcooling at the condensing unit per the 

condensing unit manufacturer’s instructions, typically 15°F 

to 16°F at the unit ventilator, subcooling at 95°F outdoor 

ambient (results in correct refrigerant distribution at the coil 

to prevent low suction temperatures)

• 

Adjust TXV for correct superheat to eliminate/minimize 

hunting, see 

Figure 79 on page 43

.

• 

Set superheat to 5°F to 7°F at the UV coil suction line when 

95°F outdoor ambient (proper system superheat for optimum 

performance). Allow system to settle for 20 to 30 minutes to 

reach stable steady state conditions and then recheck/adjust 

superheat if necessary, see 

Table 38 on page 43

.

• 

Compensate both subcooling and superheat for actual 

outdoor ambient and indoor air temperatures

• 

In windy areas, add wind baffles to condensing unit or 

build a parapet (eliminate wind effect on condensing unit 

coil for proper TXV refrigerant flow at lower ambient)

• 

For lower ambient conditions install variable speed 

condenser fan head pressure control to maintain head 

pressures between 180psig and 280psig (for proper TXV 

refrigerant flow at lower ambient).