HVAC NATE Heat Pump Questions & Answers. 100% Answers. Rated A

HVAC NATE Heat Pump Questions & Answers. 100% Answers. Rated A On an R-22 system, line diameters and lengths are typically specified for a vapor pressure drop that does not exceed what? - -6-7PSI or 6F What is the primary purpose of using flux when soldering copper or brass parts? - -Prevent Oxidation The water that results from a defrost cycle of an air to air heat pump(runoff) must? - -Drain off and away from the outdoor coil. Why must the runoff be drained off and away from the outdoor coil? - -Excessive ice can build up on the bottom of the coil and can reduce capacity. What is the component that reduces sound transmission and prevents water leaks of a package heat pump installed on a roof? - -Curb Gasket Why do you need to add a control for a heat pump indoor coil that is installed on a fossil fuel furnace? - -So the heat pump and furnace do not operate at the same time in normal heating. What happens when you energize a hermetic refrigeration compressor and the system is in a deep vacuum? - -Motor windings could become damaged. What needs to happen in order to consider an evacuation to be complete? - -System should be evacuated to a vacuum of 500 Microns or below. A system is supplied from the factory with charge for a 15 foot line set. The data plate shows the required system charge to be 5 pounds 10 ounces. The line set uses a 3/8 inch liquid line and is 25 feet long. The manufacturer's instruction sheet specifies 0.6 ounces of refrigerant to be added for each added foot of refrigerant line length. How much refrigerant is needed to completely charge the system? - -6lbs Where are drive slips typically installed? - -On the shorter sides of rectangular duct. What is a necessary check to properly set a heat anticipator? - -Heating control circuit amperage draw. A heat pump operating in normal ice free conditions maintains a certain temperature difference between the outdoor coil temperature and the surrounding outdoor ambient. What is this temperature referred to as? - -Coil TD. What is the smallest refrigerant leak that an electronic leak detector should be capable of sensing? - -.o5oz per year. When checking the pressures in an operating system with a manifold gauge set, will refrigerant oil in a hose will have an effect on the gauge? - -No What is the absolute pressure at sea level if a gauge pressure is 35 psig? - -49.7psia 100,000 BTUH output furnace. Return air temp is 65F. Supply air is 135F. What is the CFM? - -1323CFM What is the best method of repair when a residential supply diffuser is noisy because of a loose vane? - -Replace the diffuser. When performing preventive maintenance on a heat pump what should the technician check and why? - -Outdoor fan. To be certain it runs freely with no binding. What is the effect of 170 volts supplied to a 208/230 volt compressor? - -Would cause the current to increase and the motor may trip on overload. On a service call for a cooling problem with a heat pump, your inspections find a liquid line that has condensation on it. What is most likely to cause this? - -Restriction in the liquid line. What is a reason for cool air complaints when a heat pump is operating in the heating cycle? - -Excessive supply air velocities. The following measurements are recorded on an operating heat pump system. The heat pump is operating with the compressor only with no auxiliary heat: • Heat pump only supply air temperature 92°F • Heat pump only return air temperature 70°F • Outdoor temperature 54°F • Supply air temp. /auxiliary heat ON 115°F • Return air temp. /auxiliary heat ON 70°F • CFM 1228 What is the heating capacity in BTUH? - -29,177 BTU/H Inadequate heating can be caused by what? - -Dirty or clogged air filter. To minimize noise problems in residential duct systems, what is the range (recommended to maximum) of design air velocity in the rectangular main supply trunk? - -700 to 900 fpm conditions while checking a packaged heat pump in cooling. • The unit has a piston type metering device on both the indoor and outdoor coils. • Outdoor temperature 75°F • Superheat 55°F What is wrong with the system? - -Undercharged. What will you get when a capillary tube is overcharged? - -low superheat and high sub cooling What is the effect of a low charge on the switchover operations of a reversing valve? - -Reversing valves are less likely to transfer if charge is low. A technician is working on a heat pump with a capacitor start-capacitor run compressor. On initial startup, the compressor hums momentarily and the shuts down on internal overload. What is the problem? - -Too great a pressure difference on the compressor. A step down transformer has a rating of 40 VA. Its primary voltage is 120V with a secondary voltage of 24V. What is the maximum current draw of a load connected to this transformer? - -1.7amps What does a bright red or orange glow from the resistance element in a duct heater indicate? - -Flow of air is insufficient. What does the outdoor fan do during defrost on a heat pump and why? - -The fan stops to minimize defrost time. What do bent vanes on a direct drive blower wheel in an air handler cause? - -Loss in air flow, excessive motor wear, and increased noise. A split system heat pump is using thermostatic expansion valves. The system performs properly in heating but in cooling the compressor pumps down. What could this mean? - -The power element of the indoor expansion valve has lost its charge. What condition can cause a reduction from design capacity in a heat pump? - -Undersized vapor line. What is the result of excessive liquid line length or lift? - -Flash gas. What symptom could a technician expect on a heat pump system in the cooling mode if the check valve is leaking internally? - -Flooding of the indoor coil. Voltage across a closed contact in a 24V control circuit could indicate what? - -Pitted or dirty contacts. What two checks typically made first on an electronic control? - -Proper input voltage and proper output voltage. In a low voltage circuit, what does a corroded wire-to-terminal connection acts like? - -An additional resistor. How should you test the continuity of a fuse? - -Power off, fuse removed What is the first check made for most electrical troubleshooting? - -Voltage check of the supply line. The following conditions exist in a circuit that supplies power to three parallel loads. One load is resistive One load is capacitive One load is inductive How do you find the total current? - -The sum of the currents through each load. The technician is using an analog multimeter to check a run capacitor. With the meter set to ohms the needle swings toward zero and then slowly rises toward infinity. What does this tell the technician? - -The capacitor charges and discharges.