NATE: Heat Pump Troubleshooting

40 terms by roliman

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On an air-to-air heat pump system, the suction pressure and discharge pressure are low during the cooling months. What are two possible problems:

a restricted indoor metering device and a dirty air filter

On an air-to-air heat pump system, the discharge pressure and suction pressure are high during the heating months. What are two possible problems:

a dirty indoor filter and noncondensables in the system

A service call is made on an air-to-air heat pump system during the winter. When servicing the system, it is found that the outdoor coil has frost buildup and the system is operating on emergency heat. Technician A says that the system might have a defrost problem. Technician B says that the reversing valve might be leaking. Which technician is correct:

technician A

A service call is made on an air-to-air heat pump system during the winter months. The technician arrives on the job and notices that the discharge pressure is low and the suction pressure is high. What two problems could cause this symptom:

a leaking reversing valve and bad compressor valves

How can a system be tested to determine if the reversing valve solenoid is leaking internally:

A temperature measurement can be taken at the inlet and the outlet of the valve in the heating and cooling mode

What component must always be de-energized during the defrost cycle on a heat pump:

the outdoor fan

When an air-to-air heat pump is in the cooling mode, what can cause a decrease in high-side and low-side pressure:

a restricted indoor metering device

Technician A says that the check valves in a heat pump system are located in series with both metering devices. Technician B says that the check valves in a heat pump system are located in parallel with both metering devices. Which technician is correct:

Both technicians are correct

A service technician notices that a check valve needs to be replaced in a heat pump system. Because it is a ball-type check valve, it is critical for him to install the valve:

vertically, with the seat on the bottom of the valve

After troubleshooting a heat pump system, the technician concludes that the check valve is defective. He connects a recovery system and removes the refrigerant from the unit. He then proceeds to unseat the old check valve and remove it from the system. He cleans the area where the new valve will be installed, places it into position, and brazes it into the system while not protecting the valve. After a thorough evacuation, he starts the system and notices that the new valve is defective. What could have been the problem with the new valve:

A heat sink was not used and the valve warped+The valve may have been defective from the factory+The problem was misdiagnosed

Technician A says that the auxiliary heaters found on an air-to-air heat pump are used to increase the system's pressure during a defrost cycle. Technician B says that the auxiliary heaters found on an air-to-air heat pump are used to increase supply-air temperature for comfort during a defrost cycle. Which technician is correct:

technician B

When a heat pump switches into the defrost cycle, it must:

remain in defrost until the outdoor coil has reached a predetermined temperature

A defrost termination thermostat is commonly located:

on the outdoor coil, and opens at 55° F

Temperature split refers to:

the temperature difference between the air entering a coil and the temperature of the coil

Technician A says that the outdoor ambient thermostat commonly de-energizes the compressor during the second stage of heating in an air-to-air heat pump. Technician B says that the outdoor ambient thermostat used with an air-to-air heat pump commonly energizes the auxiliary strip heaters during the first stage of heating. Which technician is correct:

Both technicians are incorrect

If there is malfunction in a hold-back thermostat that is used with an air-to-air heat pump, how would this affect the system:

The system would not stay energized during defrost if the room thermostat is satisfied. This could cause freezing of the outdoor coil.

A technician arrives on a service call for an air-to-air heat pump during the heating season. She notices that the system operates normally until the defrost circuit is energized. The system stays in defrost for approximately 15 min when there is no ice or frost buildup on the coil. What could be the problem with the system:

The defrost termination switch is stuck closed

A technician receives a service call for an air-to-air heat pump. The customer is complaining about insufficient heat during low ambient conditions. Upon arrival to the job, the technician notices that the mechanical heat pump system is operating properly but the auxiliary heat is not operating. What circuit should be checked next:

the second-stage heating circuit

A technician arrives at a home on a service call for an air-to-air heat pump. After measuring the air temperature over the indoor coil and finding a temperature rise of 35° F, he determines that:

the temperature rise is sufficient

What are symptoms of an air-to-air heat pump system that has a low charge when in the cooling mode:

The low-side pressure will decrease and the indoor coil will be partially frosted

A customer calls and says that her air-to-air heat pump system is not cooling properly. Upon arrival, a technician notices that the suction line and compressor has frost buildup. Technician A says that the problem is probably a low charge. Technician B says that it is possibly a dirty air filter. Which technician is more likely to be correct:

technician B

Name two symptoms that are common to an over-charged air-to-air heat pump system with a system that has a dirty condenser.

The discharge pressure increases and the amperage increases

When an air-to-air heat pump system has an undercharge, what happens to the superheat and the subcooling of the system:

The superheat increases and the subcooling decreases

A heat pump operating in the heating mode with a dirty filter would result in:

excessive head pressure

What is the best method to recharge the heat pump system during the heating season:

weight in the exact charge

After a heat pump installation, the system will heat but not cool. The probable cause could be:

the indoor check valve is open

The technician diagnoses that in the cooling mode the compressor runs but the outdoor fan is not operating. After checking the fan motor and capacitor to be good, he concludes that:

the defrost control is defective

A heat pump reversing valve is sticking in the midway position; the manifold gauges would indicate:

lower than normal high-side pressure and higher than normal low-side pressure

An electric furnace has four 5-kw heating elements rated at 240 volts. The voltage at which the furnace has to operate is 208 volts. What will be the effect on the Btu/hr output of the furnace:

It will reduce the Btu/hr output of the furnace

With a heat pump operating in the cooling mode, the check valve at the evaporator coil is:

closed

An electric furnace using a single-stage thermostat is recording a low temperature rise. To correct this problem the technician should:

reduce the volume of air through the furnace

The difference of the ON heating cycles between fossil fuel furnaces and heat pumps during the heat mode is that the cycles are:

longer

A technician has just charged a heat pump system. She finds that the compressor does not want to start but instead hums then opens on internal overload. The compressor is a CSCR type. The more common problem would be:

defective potential relay

The thermostat second-stage heating contacts of an all-electric heat pump system serve to:

turn on the auxiliary heaters and the compressor

A technician is reading a high suction pressure at the compressor during the heating mode of heat pump system. The likely cause would be:

leaking reversing valve

Performance temperature measurements at the four-pipe connection of the reversing valve may indicate:

reversing valve leakage

A heat pump application that is using an oversized piston orifice metering device will result in:

low head pressure and high suction pressure in the cooling cycle

When speaking to a customer of a heat pump installation, you should also inform him that to conserve electricity he should:

close off dampers to rooms not used

In order to add cooling efficiency, a fan delay may be used to:

start the indoor motor after compressor start-up

A 12 X 8 return-air duct has been installed to a 3-ton heat pump system. What will be the most likely result while operating in the heating mode:

shutdown on high-pressure control

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