Ruud RP13, Installation Instructions Manual

34

With an accurate scale (+/– 1 oz. [28.3 g]) or 

volumetric charging device, adjust charge 

difference between that shown on the unit data 

plate and that calculated for the new system 

installation. If the entire system has been 

evacuated, add the total calculated charge.

IMPORTANT:

 Charging by weight is 

not always accurate since the application can 

affect the optimum refrigerant charge. Charging by 

weight is considered a starting point ONLY. Always 

check the charge by using the Charging Chart 

and adjust as necessary. CHARGING BY LIQUID 

SUBCOOLING MUST BE USED FOR FINAL 

CHARGE ADJUSTMENT.

With thermostat in the “Off” position, turn on the 

power to the furnace or air handler and the heat 

pump. Start the heat pump and the furnace or air 

handler with the thermostat. Verify that the outdoor 

unit is operating in second stage and the indoor 

air mover is delivering the correct airflow for the 

system size.

Gross Charging by Pressures

1. Following airflow verification and charge weigh-

in, run the unit for a minimum of 15 minutes 

prior to noting pressures and temperature.

IMPORTANT:

 Indoor conditions 

as measured at the indoor coil must be within 

2°F [1.1°C] of the following during gross charge 

(pressure) evaluation:

Cooling Mode: 80°F [26.7°C] Dry Bulb
Heating Mode: 70°F [21.1°C] Dry Bulb

NOTICE:

 If the Indoor temperature is above 

or below this range, run the system to bring the 

temperature down or run the electric heat/furnace 

to bring the temperature within this range. System 

pressure values provided in the Charging Chart for 

outdoor dry bulbs corresponding to conditions outside 

of these ranges are provided as reference ONLY. 

2. Note the Outdoor Dry Bulb Temperature, 

ODDB° = _____°F [_____°C]. Unit charging is 

recommended under the following outdoor 

conditions ONLY:
Cooling Mode ONLY: 55°F [12.8°C] outdoor dry 

bulb and above
Heating Mode ONLY: Between 40°F [4.4°C] and 

60°F [15.6°C] outdoor dry bulb

3. Locate and note the design pressures. The 

correct liquid and vapor pressures are found at 

the intersection of the installed system and the 

outdoor ambient temperature on the Charging 

Chart located inside the access panel cover. 
Liquid Pressure: = ______psig; Vapor Pressure = 

______psig

NOTICE:

 The refrigerant pressures provided 

are for gross charge check ONLY. These pressure 

values are typical, but may vary due to application. 

Evaporator load (indoor coil in cooling mode/outdoor 

coil in heating mode) will cause pressures to deviate. 

Note that all systems have unique pressure curves. 

The variation in the slope and value is determined 

by the component selection for that indoor/outdoor 

matched system. The variation from system to 

system seen in the table is normal. The values listed 

are for the applicable indoor coil match ONLY!
4. If the measured liquid pressure is below the 

listed requirement for the given outdoor and 

indoor conditions, add charge. If the measured 

liquid pressure is above the listed requirement 

for the given outdoor and indoor conditions, 

remove charge. 

Final Charge by Subcooling

1. After gross charging, note the designed 

subcooling value. The correct subcooling value 

is found at the intersection of the installed 

system and the outdoor ambient temperature 

on the Charging Chart located inside the access 

panel cover. 
SC° from Charging Chart = _____°F [_____°C].

IMPORTANT:

 Indoor conditions as 

measured at the indoor coil are required to be 

between 70°F [21.1°C] and 80°F [26.7°C] dry 

bulb for fine-tuned unit charge adjustment. Unit 

charging is recommended under the following 

outdoor conditions ONLY:

Cooling Mode ONLY: 55°F [12.8°C] outdoor dry 

bulb and above
Heating Mode ONLY: Between 40°F [4.4°C] and 

60°F [15.6°C] outdoor dry bulb

START-UP

Checking Refrigerant Charge (cont.)

Refrigerant