Give your HVAC Precision Tune-up Specialist (PTS) this guide to study.
There is nothing on this exam the PTS does not need to know. The tech should score 100% for general comprehension. They don’t need to know all the minor details, but they must understand why and how they are performing the tune-up tasks.
Give the PTS the HVAC technical exam, orally when ready. You will get a good feel for their understanding of the information and what they need to study further.
Cooling Tune-up Procedure
1. Check for proper evaporator airflow. A. Use a velocity meter, static pressure instrument and fan curve or temperature rise method. Target 400CFM/ton+- 50 CFM/ton. Record results.
2. Check system capacity. A. Measure and record wet/dry bulb in and out of evaporator after unit has run 15 minutes. Measure at RA grill and first SA grill. Record results.
3. Record condenser entering ambient temperature (shade).
4. Check watts. A. Measure volts and amps of fan and condensing unit. Record results.
5. Turn power to system off.
6. Clean condenser, blower, evaporator and condensate pan/drain.
7. Check capacitors.
8. Turn power back on.
9. Record altitude.
10. Recheck airflow. Record results.
11. After 15 minutes runtime, measure superheat or subcooling and adjust to +- 5F of target. Record results.
12. Record condenser entering ambient temperature (shade).
13. Record volts/amps or watts
14. Record wet/dry bulb temperature at evaporator.
15. Calculate final efficiency improvements.
16. Report results to end- user/homeowner.
Results may be calculated using one of several manual or software methods by the PTS or tech. Results can also be calculated at the office and then made available to the end-user/homeowner.
1. What is “saturation temperature”? A. The saturation temperature is the boiling point of the refrigerant. This is the temperature at which a liquid turns to a gas or a gas turns to a liquid. Also called phase change temperature and state change temperature. The saturation temperature in degrees F will increase or decrease with a change in pressure.
2. What is a “BTU”? A. British Thermal Unit. A measure of heat. About the amount of heat in a match head. 1BTU will change one pound of water 1 degree.
3. What is a “ton of cooling”? A. 12000 BTU’s. The amount of heat required to melt a ton of ice in 24 hours. 2000 pounds (ton) x 144 (latent heat of fusion) / 24 hours = 12000BTU.
4. How many BTU’s in a 3 ton AC unit? A. 36000 btu or 12000 btu per ton.
5. What are the two types of heat we measure? A. Sensible heat and latent heat.
6. What is “sensible heat”? A. The heat required to raise the temperature of air or a substance.
7. What is “latent heat”? A. Heat released during a change of state. BTU’s required to change phase. Liquid to vapor or liquid to solid. Latent heat of fusion for water is 144 BTU to change 32F water to 32F ice. Latent heat of vaporization for water is 970 BTU’s.
8. What is a “pressure temperature chart”? A. Reference card showing the pressure for refrigerants at different saturation vapor temperatures.
9. What is “superheat”? A. Degrees F of the refrigerant vapor above the saturation temperature.
10. What is “subcooling”? A. Degrees F of the refrigerant liquid below the saturation temperature.
11. What is “dry bulb temperature” and what do we measure with it? A. Dry bulb is the temperature increase/decrease we measure with a normal thermometer. We use it to measure sensible heat.
12. What is “wet bulb temperature” and what do we measure with it? A. The temperature measured by a normal thermometer with a wet sock over the bulb. The temperature indicated is the maximum temperature that water will evaporate. We use it to measure latent heat or the amount of moisture in the air.
13. What is a “CFM” and what does it measure? A. Cubic foot per minute. One CFM is a cube of air 1’ x 1’ x1’moving at 1 foot per minute. Used to measure the quantity of air in an air conditioning system. Typically 400 CFM per ton of air conditioning.
14. What is a “condenser coil”? A. Heat exchange device that rejects heat from the refrigerant and causes it to change phase from a vapor to a liquid.
15. What is an evaporator coil? A. Heat exchange device that absorbs heat as the refrigerant changes state from a liquid to a vapor. The liquid evaporates.
16. What is an “expansion device” and what are the two primary types? A. A metering orifice that is fixed or adjustable and used to meter and control the amount of refrigerant entering into an evaporator coil. The two primary types are “fixed orifice” and “TXV” (thermal expansion valve).
1. What measurements do we need to calculate real time capacity in BTU’s of an AC system? A. Measure air flow in CFM. Measure the heat removed by the evaporator coil by measuring dry bulb and wet bulb temperature on each side of the coil. The dry bulb temperature is used to measure sensible cooling. The wet bulb temperature is used to measure latent cooling. After converting the temperature difference to btu, the latent and sensible cooling are added together to indicate total cooling.
2. What measurements do we need to calculate the Energy Efficiency Ratio (EER) of an AC System? A. We must measure and calculate capacity. We must measure and calculate watts. BTU/watts=EER. A one ton unit (12000 BTU) using 1000 watts would be 12 EER.
3. What measurements are required to calculate watts or kW? A. Volts x Amps x power factor = watts. Power factor is usually assumed to be 80%, if the primary goal is to measure before/after difference in the energy efficiency of the system.
4. What is the target superheat or subcooling. When is adjustment necessary? A. The refrigerant charge is adjusted to + or – 5F of the target specified by the manufacturer. If the manufacturers target is not known, the target or adjustment is calculated using a charging calculator for superheat (fixed orifice) or charging curve chart for subcooling (TXV).
5. How do you check a capacitor? A. Disconnect power. Discharge the capacitor. Attach your multimeter. Read capacitance in MFD and compare to label.
Corrections, updates and comments on the HVAC technical exam or any other material on this site are always welcome.