Type III Certification

Maintaining, servicing, repairing, or disposing of low pressure appliances

Because a low pressure system operates below atmospheric pressure (in a vacuum) leaks in the gaskets or fittings will cause air and moisture to enter the system

• Pressurize the system by use of controlled hot water or heater blankets
• When controlled those are not feasible, use nitrogen to increase pressure
• Do not exceed 10 psig, which could cause the rupture disc to fail

• Be certain the water has been removed before placing the leak detector probe through the drain valve
• To leak test a tube, use a hydrostatic tube test kit
• Systems with open drive compressors are prone to leaks at the shaft seal

• For the purpose of opening the system for a non major repair
• Under EPA regulations a major repair mean involving the removal of any of the following components: compressor, condenser, evaporator, or any auxiliary heat exchanger coil

• Comfort cooling appliances containing more than 50 lbs should be repaired when leak rate exceeds 15%
• Commercial and Industrial process containing more than 50 lbs should be repaired when leak rate exceeds 35%

• A unit's high pressure cut-out is set for 10 psig when evacuating the refrigerant from a low pressure chiller and a rupture disc on a low pressure recovery vessel relieves at 15 psig
• Recovery from a system using R-11 or R-123 starts with liquid removal and is followed by vapor recovery

• Water must be circulated through the tubes when evacuating refrigerant
• Most low pressure recovery machines utilize a water cooled condenser that is connected to the municipal water supply
• If a chiller is suspected of tube leaks, the water sides of the evaporator and condenser should be drained

If the pressure in a system rises from 1 mm Hg to a level above 2.5 mm Hg during vacuum testing, the system should be leak checked

• 130^o F
• Fewer refrigerants are contained in the oil at this higher temperature

• Refrigerant is added through the lowest access point on the system, the evaporator charging valve
• However introducing liquid refrigerant into a deep vacuum will cause it to boil and may lower temperatures enough to freeze water in the tubes
• Intital charging is in the vapor tube, an R-11 system requires a vapor pressure of 16.9" hg or saturation temperature of 36^o F

• Equipment manufactured after 11/15/93 must be certified and labeled by an EPA approved testing organization
• All equipment mst have low loss fittings to minimize refrigerant loss when hoses are disconnected

• 25 inches Hg before
• 25mm Hg absolute after
• Once achieved, wait a few minutes and monitor the system pressure
• If pressure rises, there is refrigerant remaining in the system and recovery must be repeated

• A purge unit
• Primary purpose is to remove non-condensables (air) from the system
• A centrifugal chillers purge condensing unit takes it suction from the top of the condenser, removes air from the system and returns refrigerant to the evaporator

• 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

• Refrigerant monitor
• CFC-12, CFC-11 and HFC 134a are code grouped as A-1
• R-123 is code grouped as B-1
• All systems must be protected by a pressure relief valve, not in series