Recent studies suggest that over half of the cooling systems in operation in the U.S. are undercharged or overcharged. This causes decreased efficiency, and sometimes, premature compressor failure. The Fieldpiece Superheat and Subcooling Accessory for Refrigeration, model ASX24, measures suction line, or low side, line temperature and pressure. It then calculates actual superheat in real time using built in P/T charts. It also measures liquid line, or high side, line temperature and pressure, and calculates actual subcooling. Use it to get actual superheat and subcooling on R134A and R404A systems. Use the “T” fitting to charge to actual superheat or subcooling by putting the ASX24 in-line between your refrigerant bottle and the system.
How Does it Work?
Finding actual superheat or subcooling is easy with the ASX24. Simply hook it up to the system, let the system stabilize, and get your actual superheat or subcooling reading in real time. No charts, no calculations. It’s all done for you in the instrument. The ASX24 measures refrigerant pressure and temperature simultaneously. It then calculates and displays actual superheat or subcooling on your meter or electronic handle. It has a 1/4” industry standard fitting for actual pressure. An advanced pipe clamp k-type thermocouple especially designed for refrigeration line temperature measurement, model ATC1R, is included. Select R134A or R404A. Select English or Metric units and test.
Operation.
- Connect to COM and Volts jack. Slide ASX24 superheat head onto Fieldpiece "stick" meter, data logger, electronic handle or connect to most other meters using Fieldpiece ADLS2 deluxe test leads or AHDL1 handle.
- Set meter to mVDC range.
- Calibrate if needed (see Field calibration).
- Hand tighten 1/4” flare to suction line as close to the evaporator as possible using an EPA approved service hose (not included).
- Select refrigerant (R134A or R404A) and units (English or metric).
- Connect the pipe clamp to the suction (superheat) or liquid (subcooling) line at least six inches from the service port and slide it under the insulation for best accuracy isolating the pipe clamp from the ambient air (see Measuring Superheat and Subcooling.)
- Select parameter to display (superheat, subcooling, pressure, or temperature).
- You must wait until the system you are testing has stabilized completely before you can take an accurate superheat or subcooling reading, this usually takes about 10-15 minutes. The STABLE LED lights when superheat is stable.
- Disable Auto-off to data log any of the above parameters with the DL3 data logger.
- Once you have the superheat or subcooling reading follow the manufacturer of the air conditioner’s specifications to properly charge or diagnose the system.
Measuring Actual Superheat and Subcooling.
Superheat is the difference between the actual temperature of the refrigerant (gas) as it leaves the evaporator and the boiling point temperature of the refrigerant in the evaporator coil. After boiling, the refrigerant continues to warm up. The number of degrees it “warmed up” after boiling is called the superheat. Under worst case conditions (low load for fixed orifice systems), the refrigerant in the evaporator boils off near the end of the evaporator coil. To make sure liquid doesn’t enter the compressor under the worst case condition (low load), the AC manufacturers publish charts indicating what the superheat should be at a given indoor wet bulb measurement and outdoor air temperature.
Measuring superheat is your best indication on a fixed orifice system of the proper refrigerant charge and operating conditions. If everything else is working properly and the actual superheat is too high, add refrigerant. If it’s too low, remove refrigerant.
Subcooling is the difference between the boiling point of the refrigerant in the condenser and the actual temperature of the refrigerant as it leaves the condenser. The number of degrees the refrigerant “cools down” below the boiling point is the subcooling. Under worst case scenario (low load for TXV) the subcooling will continue to rise. If the subcooling rises to high, liquid may be backed into the compressor causing damage and catastrophic failure. On TXV systems, subcooling is the best indication of the state of charge in the refrigerant system since these systems are designed to maintain constant superheat.
Properly charging a system ensures maximum efficiency and longer equipment life.
When charging, the hose must have a Schrader valve depressor on one end to release the refrigerant from the suction or liquid line. This is the same type of hose available with most pressure gauge sets. We suggest EPA sanctioned “no leak” hoses. Exercise caution whenever working with any electricity and high pressure liquid or gas. Follow all instructions provided with equipment being serviced or installed.
Target Superheat and Subcooling.
Heed all equipment manufacturer’s specifications, warnings and suggestions above anything found in this manual. To determine the target superheat (fixed orifice system) or subcooling (charts vary dramatically from one system to another), you will typically need three things. Outdoor dry bulb (outdoor air temperature), indoor wet bulb, and the manufacturers target superheat chart or subcooling chart. You can use the ARH4 accessory head or the SRH2 Diagnostic Psychrometer for both indoor wet bulb and outdoor dry bulb. In fact, the SRH2 calculates target superheat and target evaporator exit temperature automatically based on psychometric measurements. Or you can use any Fieldpiece meter that has a temperature function along with an ATWB1 wet bulb thermocouple.
Competitive Advantages.
Many AC system analyzers include PT charts you don’t want or need. The ASX24 gives you actual superheat and subcooling in real time like the expensive analyzers do in a rugged, compact design. Used with our handles, our stick and other compatible meters, or our data logger the ASX24 displays refrigerant line pressure and pressure and calculates real time superheat or subcooling for R134A and R404A. Combined with the HVAC GUIDE® System Analyzer (link to HVAC GUIDE PRODUCT PAGE), model HG1 or HG2, the ASX24 becomes a system analyzer and then some. P/T charts for 12 of the most common refrigerants you use in HVAC/R are included, as well as the software and firmware to generate for printable work orders for customers.
Recommended Accessories and Replacement Parts.
Technicians who like the ASX24 may also enjoy these instruments and accessories: