TL;DR
Low suction pressure with high superheat confirms low refrigerant charge from a leak. Locate the leak first. Adding refrigerant without fixing the leak is a temporary fix and an EPA violation.
What you might see
- supply air temperature above setpoint
- suction line pressure below normal
- ice forming on the suction line near the unit
- compressor running continuously without reaching setpoint
Likely causes
Refrigerant leak at a service valve, flare fitting, or brazed joint depleting the charge over time
Schrader valve core leaking, identified by oil staining around the valve cap
Evaporator coil pinhole leak from acid or formicary corrosion in a corrosive environment
Refrigerant overcharged or undercharged after a previous service visit
Required tools
- Manifold gauge set (refrigerant rated)
- Electronic refrigerant leak detector
- Clamp thermometer or thermocouple
- Trane Voyager charging chart
- Certified refrigerant cylinder
- LOTO kit
Safety first
- EPA Section 608 certification is required for refrigerant handling. Unlicensed venting is a federal violation.
- Lock out the unit before opening service panels or touching electrical components.
- Refrigerant liquid or high-pressure discharge causes frostbite. Wear cryogenic gloves and safety glasses.
Procedure
- 1
Measure suction and discharge pressures at the service ports. Record both values and the outdoor ambient temperature.[1]
- 2
Calculate superheat at the suction line near the unit. Compare to the Trane Voyager charging chart for the current ambient and return air conditions.[1]
- 3
High superheat (above 20 degF target) combined with low suction pressure confirms undercharge from a leak.
- 4
Use a refrigerant leak detector to survey the full system: service valves, flare connections, evaporator coil, and all brazed joints. Mark any leak site.
Warning: Refrigerant work requires EPA Section 608 certification. Technicians without certification cannot legally handle refrigerants. - 5
Repair all confirmed leak points before adding refrigerant. Tighten flare fittings, replace Schrader valve cores, or braze pinhole leaks in accordance with applicable codes.
- 6
After leak repair, add refrigerant to bring the charge into the target superheat and subcooling range per the Trane charging chart.
- 7
Document the amount of refrigerant added, the leak location, and the repair method in the equipment log.
Sources
Trane Voyager Commercial Rooftop Service Literature, Trane (Trane Technologies)
Trane Voyager Commercial Rooftop IOM, refrigerant charge verification and superheat charging procedures (general)
View source
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