CSLB C-20 HVAC ContractorCooling and RefrigerationMedium
A technician is using a manufacturer's target superheat chart to charge a fixed-orifice metering device system. Which two measurements are required to determine the correct target superheat value from the chart?
- AOutdoor dry-bulb temperature and indoor (return air) wet-bulb temperature
- BDischarge line pressure and compressor amperage draw
- CIndoor dry-bulb temperature and outdoor wet-bulb temperature
- DSuction line pressure and liquid line temperature
Show answer & explanationAnswer & explanation
Correct answer: A. Outdoor dry-bulb temperature and indoor (return air) wet-bulb temperature
Target superheat charts for fixed-orifice systems require two inputs: the outdoor ambient dry-bulb temperature and the indoor return air wet-bulb temperature (which reflects indoor humidity load). These two values are cross-referenced on the manufacturer's chart to find the correct target superheat for charging.
Why the other options are wrong
- B. Discharge pressure and amperage are not chart inputs for target superheat lookup.
- C. Indoor dry-bulb and outdoor wet-bulb is the reversed, incorrect pairing of variables.
- D. Pressure and liquid line temperature are used to calculate subcooling for TXV systems, not to look up target superheat.
Target Superheat Chart
A manufacturer-provided chart used to determine correct superheat for fixed-orifice systems based on outdoor dry-bulb temperature and indoor return air wet-bulb temperature.
- Only used for fixed-orifice (non-TXV) systems
- Indoor wet-bulb reflects humidity load on the evaporator
- TXV systems use subcooling charging method instead
Memory trick: Outdoor dry, indoor wet — that's the superheat chart you get.