NATE: Air Conditioning Troubleshooting

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What are the symptoms of a TXV air conditioning system if it has lost its charge:

The superheat will increase and the low-side pressure will decrease

A customer who owns a split air conditioning system complains that his system has been running but his house doesn't seem to be cooling properly. When the service technician arrives on the job, he or she finds that the indoor blower is operating and the air filter is clean. The condenser fan on the outdoor unit is operating, but he or she notices that the liquid line is hot to the touch. Before connecting gauges to the system, the next step should be to:

clean the condenser coil

What are the symptoms of an air conditioning system that has a low charge:

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

A customer calls and says that her air conditioning system is not cooling properly. Upon arrival, a technician notices that the suction line and compressor have 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

What are the operating pressures of an oil pressure safety switch:

the oil pump pressure and the crankcase pressure

What is a common discharge temperature of an air-cooled air conditioning system that is used on a 90° F day:

110-120° F

What are the symptoms of an air conditioning system that has a bad compressor discharge valve:

low discharge pressure, high suction pressure, and low amp draw

What is the purpose of an EPR valve:

It increases pressure in a high-temperature evaporator coil when it is used on a dual-evaporator system

Which of the following is a possible cause for a compressor to overheat:

a low refrigerant charge

What is a possible cause of a sweat or frost pattern downstream from a sight glass and filter dryer:

a plugged filter drier

What causes the automatic expansion valve to close:

an increase in low-side pressure

A customer calls with an insufficient cooling complaint on a 90° F day. Upon arrival it is found that the system, using R-22, is operating at 50 psig on the low side and 150 psig on the high side. Further investigation indicates that the evaporator coil is partially frosted on one circuit of the distributor. Technician A says that the system has a low charge and must be leak-tested. Technician B says that the capillary tube from the distributor is partially restricted. Which technician is correct:

technician B

What type of problems can be caused by an oversized air conditioning system:

short cycling and insufficient dehumidification

What types of symptoms will be present if the sensing bulb of a TXV is not properly connected:

high suction pressure and low superheat

An air conditioning unit has a suction line that is frosted up to the compressor. What faults could cause this to occur:

a dirty evaporator coil+a plugged air filter+a bad indoor blower relay

If 24 volts are present to the contactor coil on an air conditioning system and the condenser fan or compressor is inoperative, which of the following could be at fault:

a blown fuse

A customer calls with an insufficient cooling complaint. Upon arrival to the service call it is found that the system is using R-22 with the high-side pressure at 290 psig and the low-side pressure at 85 psig. The ambient temperature is 85° F and the indoor wet bulb (WB) is 60° F. Technician A says that, more than likely, the condenser is dirty. Technician B says that the system's pressures are common for this type of day. Who is correct:

technician A

If a TXV sensing bulb had lost its charge, what effect would this have on the air conditioning system:

It would cause the low-side pressure to decrease

A customer calls with an insufficient cooling complaint. Upon arrival to the service call it is found that the outdoor condensing unit is operating, but the indoor blower is not in operation. Technician A says that it is possible that it is a bad fuse to the furnace. Technician B says that the control transformer could also be at fault. Who is correct:

Both technicians are incorrect

A party-store owner tried to adjust the water valve on his water-cooled condensing unit, then he called for assistance from an HVAC/R service technician. It was found that when servicing the unit, the outlet water temperature was too low. Technician A says that turning the adjustment stem on the water valve clockwise will close the valve, and this will cause an increase in high-side pressure. Tehnician B says that turning the adjustment stem on the water valve counterclockwise will close the valve, and this will increase the high-side pressure. Which technician is correct:

technician B

What are two common symptoms of an overcharged air conditioning system that uses a capillary-tube-type metering device:

an increase in suction pressure and an increase in discharge pressure

Name two symptoms that are common to an over-charged air conditioning system and a system that has a dirty condenser.

The discharge pressure increases and the amperage increases

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

The superheat increases and the subcooling decreases

If a rooftop air conditioning system does not have any means of low ambient protection, what will be two symptoms of the system when operating under a low ambient condition:

high superheat and low discharge pressure

What are two common symptoms of a rooftop air conditioning system that operates with a reverse-acting high-pressure control stuck in the closed position:

condenser fans operating during a low ambient condition and a low suction pressure

What are two problems that can cause an air conditioning system to have an excessively high superheat:

an uninsulated suction line and a restricted metering device

What are two common problems that can cause a sight glass in an air conditioning to have bubbles:

an undercharge and low ambient conditions

A technician arrives on the job and the customer complains that there is no cooling on his rooftop unit. Troubleshooting the system, the technician finds that the compressor is faulty. He notices that there is another faulty compressor laying next to the unit. A further check shows that the crankcase heater is electrically burnt open. What type of damage is most likely to have been done to the compressor:

broken rings+broken valves+seized bearings

After a compressor motor has been severely burnt, what accessory must be added as an aid to rid the air conditioning system of acid:

an acid-core suction line drier

When troubleshooting a split-system air conditioner, it is found that the compressor motor is humming but not starting. Technician A says that it could be an open internal overload protector. Technician B says that it could be a blown fuse. Which technician is correct:

Both technicians are incorrect

A technician receives an air conditioning service call stating that the system is operating but isn't cooling properly. When the technician arrives, she notices that the compressor has recently been changed and it is an R-22 system. She checks the indoor air filter and the condenser coil. Both are clean and both coils seem to have adequate airflow. When she connects her gauges she notices that the suction pressure is 95 psig, the high-side pressure is 285 psig, and the ambient temperature is 80° F. What is most likely to be the problem with the system:

The system was improperly serviced and it has air trapped in the condenser or the unit has been overcharged

An air conditioning system that uses a fan center has an inoperable indoor blower. When the thermostat is set for cooling and dialed below room temperature, a test with the voltmeter shows that there is 24 volts across terminals "R" and "G" at the terminal block. What is the problem with the system:

a bad thermostat

When testing an indoor blower control circuit and the cooling circuit on a fan center, what terminals should read 24 volts if the air conditioning system is in operation:

("Y" and "C") and ("G" and "C")

Which of the following problems can cause a decrease in a system's pressures and possible icing of the evaporator coil:

a missing air filter+improper rotation of the indoor blower+blower too small

A split-system air conditioner that uses a piston-type metering device is to be charged with R-22. Technician A says that the outdoor dry-bulb temperature is needed to determine the proper superheat. Technician B says that the indoor wet-bulb temperature is needed to determine the proper superheat. Which one is correct:

Both technicians are correct

A 220-volt 30-amp motor circuit keeps tripping the breaker after the motor is started. The starting amperage is 60 amps. When measuring the amperage of the circuit, this is drawn for a brief moment. After startup, the amperage drops to 22 amps and then the breaker trips. What is the problem with the circuit:

a defective circuit breaker

A rooftop package system keeps tripping out on the high-pressure switch. What are three possible causes for this problem:

dirty condenser, bent condenser fins, and air recirculating over the condenser

What are two common symptoms of refrigerant leaks in an air conditioning system:

partially frosted evaporator and high superheat

A system that is being serviced has been evacuated down to 500 microns. When the gauges are closed and the vacuum pump is turned off, the pressure starts to increase and stops at 1,000 microns. Technician A says that the system has a leak and needs to be repaired. Technician B says that the system has moisture present and it needs to be evacuated longer. Which technician is correct:

technician B

What are common methods that are used for leak-testing a system:

a vacuum test+oil traces around fittings+soap bubble solution

What is the purpose of a CPR valve:

It is used to control refrigerant pressure in the compressor crankcase

What is the common cause of a compressor burnout:

improper system evacuation during installation+short cycling of the system+excessively dirty condenser

Which of the following is a common cause of an excessively low superheat on a TXV system:

a sensing bulb improperly connected to the suction line

What are three methods for controlling a system's high-side pressure during low ambient conditions:

flooding the condenser, cycling condenser fans, and dampering condenser air

What is a common temperature difference between the condensing temperature on an air-cooled condensing unit and the outdoor ambient temperature:

20 to 30° F

What controls are used on air conditioning or refrigeration systems that incorporate an automatic pump-down system:

A thermostat cycles the liquid-line solenoid, and a low-pressure switch controls the compressor

A customer calls and complains that his air conditioning system is not operating properly. It is noticed that the compressor is not operating. A check on the run capacitor shows that there is 33 uf and the rating on the capacitor is 40 uf. Technician A says that the capacitor is good because it is within its normal 20% range. Technician B says that the capacitor is bad because it is not within its 10% range. Which technician is correct:

technician B

A system that is operating with a clear sight glass shows:

the sight glass is full of liquid+the sight glass is full of gas

Technician A says " When charging a system using the superheat method, adding refrigerant to the system will increase the superheat." Technician B says "When charging a system using the superheat method, adding refrigerant will decrease the superheat." Which technician is correct:

technician B

What is the purpose of the TXV:

It keeps a constant superheat in the evaporator

A liquid-charged TXV bulb will:

always have some liquid present in the bulb and diaphragm

When using a vapor-charged TXV bulb, it is necessary to have:

the sensing bulb at a lower temperature than the valve body

A customer calls and complains that her high-efficiency air conditioning system is operating, but is not cooling properly. Further investigation shows that the system is using a TXV type of metering device. A subcooling check shows that the system appears to have the proper charge. A test shows that the superheat is 30° F when it is supposed to be 15° F. What could be the problem:

the external equalizer could be plugged

A system that uses a thermal electric expansion valve:

can use the thermal electric expansion valve instead of a liquid-line solenoid as part of the pump-down system

What are possible problems that can cause the discharge-line temperature on an air conditioning system to be cool to the touch:

The system could be undercharged+The compressor could have bad valves+The system could have a restricted metering device

A customer calls to complain that his central air conditioning system is not cooling properly. The technician arrives on the job. He or she notices that the indoor blower has adequate airflow and the outdoor condenser fan is operating, but the compressor is not operating. After pulling out the electrical disconnect, the technician measures resistance across the compressor motor windings. The readings are as follows: run to common, infinite ohms; start to common, infinite ohms; and run to start, 10 ohms. What could have caused this condition:

an open internal overload protector

A commercial customer calls complaining that her rooftop air conditioning system is not operating. The technician arrives on the job and sets the thermostat to cooling, then notices that the indoor fan is not operating. The technician then sets the thermostat to the fan on and it still does not operate. What two terminals must be tested for 24 volts to ensure that the problem is not the thermostat:

"G" to "C"

A commercial customer calls on a 90° F day, complaining that his rooftop unit is running but not operating properly. The technician arrives on the job and the customer shows him an invoice from the spring season. The invoice states that 2 lb of R-22 were added to the system. After connecting his or her gauges, the pressure reads 88 psig on the low side and 300 psig on the high side. What is the most likely system problem:

The system has been overcharged+The system has air trapped in the condenser

Which of the following could be the cause for a system's discharge and suction pressure being low:

a restricted metering device

What problem or problems can cause low discharge and suction pressure:

an undercharged system+insufficient airflow over the evaporator coil

What problem can cause an increase of discharge pressure and an increase of suction pressure:

an overcharged system

What problem or problems can cause the discharge pressure to be low and the suction pressure to be high:

bad compressor valve

Which of the following can cause excessive subcooling:

an overcharged system

Which of the following can cause low superheat in a TXV system:

an uninsulated TXV sensing bulb

What three things can prevent an air conditioning system from releasing heat at the proper rate:

a dirty condenser, recirculation of condenser air, and a defective condenser fan

What three things can prevent an air conditioning system from absorbing heat at the proper rate:

a dirty evaporator coil, a defective evaporator fan, and an iced-up evaporator coil

What component is most often the cause of a start capacitor failure:

a start relay

A compressor motor starts and operates for a short period of time and cycles on the external overload protector. What are two possible problems that could cause this:

low voltage and a faulty start relay

Technician A says that to manually pump down an air conditioning system with a two-position service valve, the liquid line must be front-seated and the high- and low-side pressure will decrease to 0 psig when the pump-down is complete. Technician B says that to manually pump down an air conditioning system with a two-position service valve, the liquid line must be front-seated and only the low-side pressure will decrease to 0 psig when the pump-down is complete and the high side will drop slightly. Which technician is correct:

technician A is correct

Technician A says that if you connect 208 volts to the primary side of a 240-volt/ 24-volt transformer, the transformer will burn out. Technician B says that if you connect 208 volts to the primary side of a 240-volt/24-volt transformer, the control circuit voltage will drop. Which technician is correct:

technician B

When a high-efficiency split air conditioning system has a plugged metering device, what symptoms might occur:

a low amp draw, a decrease in high-side pressure, and a decrease in low-side pressure

Why is it unsafe to operate an air conditioning system with a low charge:

It can seize the compressor because of excessive heat+It can seize the compressor because of lack of lubrication

The technician observes a pressure drop of 25 degrees across an air conditioning evaporator coil at start-up. This drop would indicate:

lack of airflow

Air filters should be replaced:

whenever necessary

On an R-22 air conditioning system, the suction-line filter drier should be changed when the pressure drop dictates:

3 psig

A compressor having tight bearings would cause the current value to:

rise more than normal

The technician observes that the compressor is not operating. The compressor windings read 5 ohms start to run, run to common is opened, and start to common is opened. The technician concludes that:

the internal overload is opened

The temperature range of the suction line from an air conditioning system should be:

50-65° F

Superheat is found in an air conditioning system in the:

evaporator and compressor

A hard-start kit for an air conditioning system:

increases starting torque

An air conditioning system using a fixed-orifice metering device and with noncondensables in the system will cause:

run with high head and high suction pressure

The internal overload of an air conditioning compressor senses winding temperature and:

current in the compressor circuit

A restricted air filter in an air conditioning system can be identified by:

low superheat

The best description of a relay would be:

contains a solenoid coil and one or more sets of contacts

Insufficient airflow can be caused by:

an increase of air leakage from ductwork

A hard-start kit consists of:

a start capacitor and a solid-state relay

Which of the following will cause excessive discharge pressures on an air conditioning system:

condenser air being recirculated over the condenser+air trapped in the condenser due to poor service procedures+an overcharged air conditioning system

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