1. Refrigerant Charge Procedures
July 2007
Cleaning, Vacuum &
Refrigerant Charge Procedures

2. Discharge temperature
Monitoring Operative Parameters
Suction pressure
at the compressor
Discharge pressure
at the compressor
Suction temperature
at the compressor
(total superheat);
Discharge temperature
at the compressor
Suction temperature
at the evaporator outlet
(evaporator superheat)
CONDENSER
Liquid temperature
at the expansion valve inlet
(liquid subcooling)
EVAPORATOR

3. Basic Instrumentation
A basic refrigerant recovery equipment is required:
A Digital Weighing Platform
used to avoid overfilling the Recovery Cylinder and ensuring that the exact amount of refrigerant charged into the system can be logged. This aids monitoring of consumption and leakage.
Refrigeration Storage Tank
with two connection ports to enable charging of liquid and extraction of vapour simultaneously
A Vacuum Pump
that removes moisture and non-condensable gases after the system has been opened for maintenance and repair.
Recovery Unit
with oil-free compressor and pressure manometers
Manifold
with pressure and suction gauges and connection hoses. This gives a full overview of system performance and visually monitoring the system during refrigerant recharging.
A Vacuum Gauge
used to determine if proper vacuum has been obtained. It will also help indicate if the system is not leak-tight.
An Electronic Leak Detector
can detect up to 5 ppm and features a six-segment visual leak size indicator and a variable frequency audible alarm.

4. Cleaning the Refrigerant Circuit
1) The circuit must be flushed with nitrogen in order to remove oil residues and other impurities.
2) Close the rotalocks connections.
3) Remove the filter drier and let both the low and high pressure sides opened.
4) Start flushing both sided with nitrogen at least 3 times.
REMOVE
NITROGEN
NITROGEN

5. Moisture in Refrigeration Systems
Visible Moisture
Water Droplets (uncommon, but it can occur)
Invisible Moisture
Water Vapor (found in all gases and solids)
Air in the piping
“Wet” Refrigerant
Leaks Under a Vacuum Condition
Copper and Brass Components
System components exposed to atmosphere during assembly

6. Moisture in Refrigeration Systems
Visible Moisture Problems
FREEZE
OBSTRUCTS THE PROPER FUNCTIONING OF THE COMPRESSOR
AND THE REFRIGERATION SYSTEM
ICE CRYSTAL FORMATION AT THE POINT OF EXPANSION
CAP TUBE BLOCKED
EXPANSION VALVE
Invisible Moisture Problems
MOISTURE + METALS = CORROSION
MOISTURE + REFRIGERANT = ACID
CFC & HCFC & HFC: Hydrolyze to form Hydrochloric Acid or Hydrofluoric Acid
Acid formation is accelerated by heat
Copper and brass will be attacked (hot surfaces and bearings)
MOISTURE + REFRIGERANT + OIL = SLUDGE
REDUCE SERVICE LIFE AND INCREASE CONDENSING PRESSURE
HIGH DISCHARGE PRESSURE AND TEMPERATURE
MECHANICAL AND ELECTRICAL COMPRESSOR FAILURE

7. Differential pressure Zero absolute pressure
Vacuum
How can we get the water out?
We must boil it
We can’t raise the system temperature to 100 °C.
We can lower the system pressure to a point that water boils at ambient temperatures (vacuum )
Measured pressure
Absolute pressure
Positive pressure
Atmospheric pressure
(0 barg or bara)
Differential pressure
Negative pressure
(vacuum)
Absolute vacuum
Zero absolute pressure

8. AS PRESSURE DECREASES, THE BOILING POINT DECREASES
Vacuum
Basic Physics:
AS PRESSURE DECREASES, THE BOILING POINT DECREASES
1.013 bara
0.98 bara
26 °C
100 °C

9. Vacuum Pump Two stage rotary vacuum pumps most common for service;
larger cubic meter per minute capacity;
slightly heavier than single stage of same capacity;
can achieve deeper vacuum than single stage because second stage takes over at the level first stage stops;
can pull to one micron of Mercury vacuum.
2nd stage
1st stage

10. Vacuum Procedure
First of all, the compressor must be isolated from the system. It is essential to connect the vacuum pump to both the LP & HP side in order to avoid dead-ending parts of the system.
Pull down the refrigeration circuit under a vacuum of:
R407C, R410A  0.1 mbar (10 Pa, Torr)
R22  1 mbar (100 Pa, 0.75 Torr)
Low-pressure gauge
(B) High-pressure gauge
(C) Slowly open
(D) Vacuum pump turn on

11. Vacuum Procedure
3) When the correct vacuum level is reached, the circuit must be isolated from the pump.
4) Wait at least for 30 minutes.
5) If the pressure rapidly increases, then the circuit is not leak tight. Locate and repair leaks. Restart from step 1).
If the pressure slowly increases, then the circuit contains moisture. Break the vacuum with nitrogen gas and repeat steps 1), 2), 3).
Leakage
Moisture
Pressure [bar, Pa, Torr]
Vacuum level
Tight & dry
Time [min]
The vacuum level should be reached and maintained for at least 4 hours (it depends on the length and size of the circuit): it will guarantee that the circuit is both tight and fully dehydrated.

12. July 2007
Refrigerant Charge
Zeotropic refrigerant mixtures (i.e. not defined by a single pressure-temperature relationship) such as R407C must always be charged in liquid phase. For the initial charge, the compressor must be stopped and service valves must be closed.
Charge refrigerant as close to the nominal system charge as possible before starting the compressor; then, slowly add refrigerant in liquid phase on the low-pressure side, as far away as possible from the running compressor.
Connections size for R22-R407C-R410A: 1/4“

13. Refrigerant Ruler
The refrigerant ruler is used to calculate the pressure and temperature of refrigerants.
Set the cursor on the refrigerant pressure and read off the corresponding temperature.
The values are shown in metric and US units.

14. Tsat cond – Tliq = SBC ≈ 5 – 10 °C
Subcooling
Subcooling is defined as the difference between the refrigerant liquid temperature and its saturation temperature. It can be used to check the correct refrigerant charge.
Subcooling can be measured by:
placing a thermometer on the expansion valve inlet, reading the liquid temperature Tliq.
placing a pressure gauge on the inlet (or outlet) of the condenser coil, reading the condensing pressure pcond. This pressure is strictly linked to the saturation temperature of the refrigerant Tsat cond (bubble point temperature if zeotropic mixtures, like R407C).
Pressure gauge  pcond
Tsat cond
Thermometer  Tliq
Tsat cond – Tliq = SBC ≈ 5 – 10 °C

15. Superheat Tasp – Tsat evap = SPH ≈ 5 °C
Superheat is defined as the difference between the refrigerant vapor temperature and its saturation temperature. It can be used to monitor the functioning of the expansion valve.
Superheat can be measured by:
placing a thermometer on the evaporator outlet, reading the vapor temperature Tvap.
placing a pressure gauge on the evaporator outlet, reading the evaporating pressure pevap. This pressure is strictly linked to the saturation temperature of the refrigerant Tsat evap (dew point temperature if zeotropic mixture, as R407C).
pevap  Pressure gauge
Tsat evap
Tasp  Thermometer
Tasp – Tsat evap = SPH ≈ 5 °C

16. Subcooling & Superheat for R22

17. Subcooling & Superheat for R407C

18. Pump Down Procedure
When a leak is detected or a compressor replacement is required, it could be useful to perform a “pump down” procedure.
The term means the operation by which all the refrigerant inside the circuit is pumped on the high pressure side (i.e. on the condenser side), making it possible both to operate on the low pressure side and to recover the major amount of refrigerant.

19. Pump Down Procedure
Close the shut off valve placed after the liquid receiver at the output of the condenser coil.
Let the compressor run until the low-pressure manometer goes down to bar; the lower is this pressure, the minimum is the refrigerant loss.
bar
CLOSED ON

20. Pump Down Procedure 3) Switch the main circuit breaker off.
4) Close the rotalock on the discharge side of the compressor; if the compressor miss rotalocks, close the shut off valve on the high pressure side.
CLOSED
OFF

21. Removing Liquid Refrigerant
Remove the refrigerant from the HP side of the system through any connection or valve located on the liquid line by using a refrigerant recovery unit and storage tanks.
Make a note of the weight of refrigerant mass reclaimed.
OFF

22. Refrigerant Charge Overview
R407C – R410A 1
Open any shut-off valves present in the machine to ensure that all of the components will be evacuated; 2
Connect a pump to empty the schrader connections efficiently, or to the 1/4" SAE connections present on the intake and delivery sides of the compressors; 3
Connect the refrigerant cylinder to the loading connections; 4
Create a vacuum within the lines while maintaining the pressure below 100 Pa absolute (0,7 mm Hg) for a long time in order to evacuate the air as well as any traces of humidity. It is preferable that the vacuum is reached slowly and maintained for a long period of time;
Create a vacuum within the lines whilst maintaining the pressure below 10 Pa absolute (0,07 mm Hg) for a long time in order to evacuate the air as well as any trace of humidity. It is preferable that the vacuum is reached slowly and maintained for a long period of time; 5
Wait for a build up period of 100 seconds and check that the pressure has not exceeded 200 Pa absolute. Generally, in the case of suspicion of strong hydration of the circuit or an extremely extensive system, it will be necessary to break the vacuum with anhydrous nitrogen and then repeat the evacuation procedure as described; 6
Break the vacuum by performing a preload from the R22 coolant cylinder;
Break the vacuum by performing a preload in liquid phase from the R407C or R410A coolant cylinder;

23. Refrigerant Charge Overview
R407C – R410A 7
After having started the compressor, slowly complete the loading phase until the pressure within the lines has been stabilized and the gaseous bubbles have disappeared from the flow sight glass; 8
The loading process must be controlled in environmental conditions with a delivery pressure of approximately 18 bar (equivalent to a saturated temperature of 48°C); in the case of units with ON/OFF condensation controls, avoid switching the condenser fan on and off, which may partially obstruct the intake surface. It is wise to check that the sub-cooling of the liquid at the entry of the thermostatic valve is between 3 and 5°C below the condensation temperature read on the scale of the pressure gauge and that the overheating of the vapour at the exit of the evaporator is equal to 5-8°C.
The loading process must be controlled in environmental conditions with a delivery pressure of approximately 18 bar (equivalent to a dew temperature of 48 °C and a bubble temperature of 43°C); in the case of units with ON/OFF condensation controls, avoid switching the condenser fan on and off, which may partially obstruct the intake surface. It is wise to check that the sub-cooling of the liquid at the entry of the thermostatic valve is between 3 and 5 °C below the condensation temperature read on the scale of the pressure gauge and that the overheating of the vapour at the exit of the evaporator is equal to 5-8°C.

24. Lubrication & Oil Adjustment
Compressor oil drain
• Open the suction port, or the sight glass port (when fitted);
• Move the compressor slowly to a horizontal position and recover the oil through the compressor suction connection port, or from the oil sight glass opening.
• Note: the large scroll compressor is equipped with an oil drain connection and can therefore be drained of its lubricant in a vertical position. In this case, pressurize the LP side of the compressor (by using dry nitrogen).
• Pick an oil sample for analysis if needed (i.e. operational installation).
• Before re-installing the compressor, or replacing the sight glass, replace the gaskets by new ones (suction & discharge ports, sight glass gasket). Check the old lubricant for acid content using an acid test kit.
• Install a new filter drier. An anti-acid type cartridge has to be used if the acid test is positive. The anti-acid filter drier has to be replaced by a standard cartridge after a few days when the system is acid free.
Oil drain

25. Lubrication & Oil Adjustment

26. Lubrication & Oil Adjustment
It is not required to add oil whenever the refrigerant lines don’t exceed 30 meters.
When the lines exceed 30 meters, and vertical lines are also present, it is advisable to add oil according to the number of siphons along the gas line.
Fill in with water one siphon, pour it in a graduate cup and multiply this quantity for the number of siphons: this is the amount of oil to add to the system. NO
OK! NO

27. Additional recommendations
Lubrication & Oil Adjustment
Additional recommendations
• After adding oil, allow the compressor to run fully loaded for 20 minutes and re-check the level in the oil sight glass. This level should be between 2/4 and 3/4.
• Be careful not to add more oil than necessary. The following adverse conditions can occur if excessive oil is present:
- Failure of valves and pistons or scroll involutes due to oil slugging.
- Excessive carry over of oil loss of evaporator performance due to oil level built-up in the low side of the system.