RECHARGING TECHNIQUES
Refrigerant is added through the lowest access point on the system, the evaporator charging valve. However, intro‐
ducing liquid refrigerant into a deep vacuum will cause the refrigerant to boil and may lower temperatures enough to
freeze water in the tubes. Therefore, initial charging is in the vapor phase. Before charging with liquid, an R‐11 refrig‐
eration system requires a vapor pressure of 16.9” hg. vacuum, or a saturation temperature of 36
°
F.
RECOVERY REQUIREMENTS
Refrigerant Recovery and/or Recycling equipment manufactured after November 15, 1993, must be certified and la‐
beled by an EPA approved equipment testing organization to meet EPA standards. All equipment must have low loss
fittings to minimize refrigerant loss when hoses are disconnected.
The following is a list of the required levels of evacuation for Low Pressure appliances:
Using recovery or recycling equipment manufactured or imported before Nov. 15, 1993
25 inches Hg
Using recovery or recycling equipment manufactured or imported on or after Nov. 15, 1993
25 mm Hg absolute
Once the required vacuum has been achieved, the technician should wait for a few minutes and monitor the system pres‐
sure. If the pressure rises, indicating that there is refrigerant remaining in the system, recovery must be repeated. When
leaks in an appliance make evacuation to the prescribed level unattainable, the appliance should be evacuated to the
lowest attainable level prior to a major repair.
REFRIGERATION NOTES
(Review vapor / compression system in introduction)
The use of a large vacuum pump could cause trapped water to freeze. During evacuation of systems with large
amounts of water, it may be necessary to increase pressure by introducing nitrogen to counteract freezing.
If a strong odor is detected during the recovery process, a compressor burn‐out may have occurred. When recovering re‐
frigerant from a system that experienced a compressor burn‐out, watch for signs of contamination in the oil.
Because chillers using refrigerants such as CFC‐11 and HCFC‐123 operate below atmospheric pressure, they require a
purge unit. The primary purpose of a purge unit is to remove non‐condensables from the system. A centrifugal
chiller's purge condensing unit takes its suction from the top of the condenser, removes air and other non‐
condensables from the system, and returns refrigerant to the evaporator. Although a high efficiency purge unit dis‐
charges a low percentage of refrigerant with the air they remove, frequent purging and subsequent refrigerant loss can
indicate that a leak is allowing air into the system. High discharge pressure is also an indication of air in the system. Ex‐
cessive moisture collection in the purge unit can indicate tube leakage.
To protect the system from over‐pressurization, low‐pressure chillers typically use a rupture disc mounted on the
evaporator housing. The typical design burst pressure for a rupture disc is 15 psig.
SAFETY
(Additional Safety and shipping information is covered in the core section of this manual.)
ASHRAE standard 15 requires a refrigerant monitor that will sound an alarm and automatically start a ventilation sys‐
tem in equipment rooms before the refrigerant concentration reaches the TLV‐TWA, (threshold limit value‐time
weighted average).
A refrigerant monitor is required for all ASHRAE refrigerant safety groups.
CFC‐12, CFC‐11, and HFC‐134a are code grouped as A‐1. R‐123 is code grouped as B‐1.
All refrigeration systems must be protected by a pressure relief valve(s) (must not be installed in series).
Additional Safety and shipping information is covered in the core section of this manual.
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