- Blends operate at different pressures than R-22.
- It’s important to charge and tune systems to the replacement refrigerant pressures
- Tuning systems to Superheat and Subcool is critical.
- PT Charts for blends have two (2) columns.
It is critical to charge and tune systems to within the stated parameters from the manufacturer.
In the past many techs have grown accustomed to charging by “feel” (“beer can cold”) or by “Return Air” or by matching what was recovered. With replacement blends this is a recipe for disaster. You must go back to the basics and ALWAYS Charge by Superheat and Subcool.
- Always charge blends as a liquid only (refer to cannister instructions).
- Always charge through the liquid line.
- Initially charge to 80% of the nameplate or amount recovered (whichever is less).
- Once operational, allow system to stabilize (generally 10-15 minutes).
- Chargefixed metering devices to Superheat, charge Adjustable metering devices first to Subcool and Tune to Superheat.
- Slowly meter refrigerant into suction line to achieve proper Superheat and Subcool.
- In most cases, TXVs will be closed 1-4 turns to achieve proper Superheat with TdX 20.
- Superheat tuning (conditions based):
Low load conditions = lower end of SH range
High load conditions = higher end of SH range
- Recommend using Yellow Jacket Liquid Charge Restrictor (Figure 2) for suction line charging.
- Allow system to stabilize (generally 10-15 minutes) in between charge and valve adjustments.
- When applicable, break the vacuum with appropriate suction pressure charge before starting the system.
- Generally Subcool should be between 8-12 F with 12-20 F Superheat at the compressor