Nate AC Service Test Questions and Correct Rationales Graded A+.

  A technician has determined a supply in a flexible duct system is leaking. What should be checked? - Answer: All connections inner and outer layers. Electronic air cleaners can operate with internal voltages as high as? - Answer: 5000v Why do some electromechanical type thermostats require connections to both the hot side and common side of the low voltage transfromer - Answer: Display lights must be powered using both sides of the line the continuity reading on a functional fuse will be - Answer: 0 ohms a compressor with proper voltage and a hard start relayt and capacitor draws lock rotor amps on startup. what is the problem? - Answer: the technician believes that a hermetic compressor has a permanently openn internal overload protectio the technician should test the compressor while it is? - Answer: cool outdoor condensing units that are installed in areas where flooding is possible must - Answer: be mounted above flood level In a low voltage circuit, a corroded wire-to-terminal connection acts in the circuit like an - Answer: additional resistor a system with a reciprocating compressor is pumped down and the power is shut off. if the suction pressure rises very rapidly this is an indication that the - Answer: if an air conditioning system needs to operate in a low ambient condtion, the condenser may become to effiecent - Answer: the head pressure becomes too low and the condenser fan motor needs to be slowed or stopped to achieve a specific seer rating which components must be matched - Answer: condensing unit and evaporator on a residental no cooling call, typically the first check would be - Answer: if the thermostat is calling for cooling in an economizer system the enthalpy control is used to measure - Answer: both temperature and moisture content an air conditioner refriderant circut should be evacuated to a minimum of - Answer: 500 microns what steps are necessary to clean a two row curved condenser coil - Answer: separate the two rows of coils, spray all surfaces with proper coil cleaner and water flush return air leakage in a hot attic will - Answer: decrease capacity When a split system air conditioner has a counterflow air handler, what are the best locations for return air grilles? - Answer: on a sidewall next to the ceiling the lubricating oil primarily ised with r-22 is - Answer: mineral oil based other than using a two-stage compressor what is another method for capacity control - Answer: liquid line receiver a system air flow check is used to diagnose - Answer: humidity problems what precautions need to be taken with a packaged ac system with ductwork installed outside - Answer: it must be insulated and weatherproofed which of the following is a proper operation for a packaged air conditioning system using an electric control board - Answer: the blower condenser fan and compressor comes on at the same time which of the following should be done to reduce vibratiion transmission in sheet metal ductwork - Answer: add isolations collors what does a test of the compressor oil after a burnout indicate - Answer: acidity a 120v x 24v step down transformer has a rating of 40va. must not be connected to more than - Answer: 1.7 amps 40/24=1.666777 what is the maximum acceptable supply voltage tolerance for a 120v circuit - Answer: 5% in a simple refrigeration system the refriderent boils in the - Answer: evaporator electronic air cleaners do not remove - Answer: animal fur a delay on make relay delays load from - Answer: from energizing after a fixed time after a cycle for indoor air quality purposes the minimun distance between and economizer and a plumbing vent iut - Answer: 10ft S.E.E.R stands for - Answer: seasonal energy efficiency ratio the purpose of flux is to - Answer: reduce oxidation to properly check the compoerssor and its line volatage wiring, the technicain should mesure resistance at the - Answer: load side of the compressor contactor the suction line instulation is important to control condensation and what? - Answer: minimize heat transfer the slab of a packaged air conditioner at grade level should be - Answer: isloated from the structure to minimize noise using the attached diagram the 2TH will change the fan motor speed based on - Answer: According to fire protection codes, when should fire dampers be used - Answer: In any air duct that passes through a two hour fire rated wall or partition of a light commercial installation what does a red or orange glow from the resistance elements in a duct heater indicated - Answer: flow of air is insuffient what is the typical method of staging a two stage compressor in a air conditionoing system - Answer: it is based on the deviation from the thermosetpoint when an air conditioner with a thermostatic expansion valve is installed is overcharged, the excess char sgould be removed by recovering some charge and checking - Answer: system pressure which of the following is a typical use of an outdoor ambient thermostat in a split commercial system air conditioner - Answer: increase blower speed in high ambient a residential supply diffuser that is noisy because of a loose vane is best serviced by. - Answer: replacing the diffuser most safety controls are wired in - Answer: series with the load service site condtionms - Answer: the system blower is operating normally but the supply registers are to restrictive will a capacitor start capacitor ruun motor that has an open run capacitor start - Answer: no it would be unable to start without the run capacitor on a three ton unit installation, the measured airflow euals 1550 cfm,what does this indicate - Answer: excess airflow which of the following are the first two checks typically made on a electronic control> - Answer: Proper input voltage and proper output voltage. an important consideration when installing a motorized economizer is to check to be certain that - Answer: the vanes operate without binding during an annual service check up, it is discovered that there is a moderate amount of resistance on a bellyband crankcase heater. what does this condition indicate - Answer: the crankcase heater will operate which microfarad value indicates a good start capacitor rated at 145/175 mfd a)130 b)160 c)180 d)190 - Answer: 160 What is the component that reduces sound transmission and prevents water leaks of a package heat pump installed on a roof? - Answer: Curb Gasket how would a technician repair a 1" hole in a section of duct board - Answer: cut out the hole, and fabricate, staple and tape a plug in place to fill the hole a technician finds a R-410a system with a suction pressure of 105 psi. this indicates that - Answer: it is undercharged a high pressure limit control is used to shut down a compressor is condensing pressure becomes excessive, is typically installed to sense: - Answer: compressor discharge line pressure thermostatic expansion valves meter refrigerant flow to a coil to maintain - Answer: superheated refrigerant leaving the coil which of the following is a likely problem if the air across the evaporator of an air conditioner has a high temperature differential - Answer: dirty filter or evaporator load across T1 & L1 when compressor contractor is de-energized and compressor windings in tact. - Answer: 230v Springs are used to open the contacts when the magnetic field is de-energized. The coils of a contactor are energized by the control voltage of the system. This voltage is typically 24, 120, 208/230, or 460 volts. how should a mercury bulb be disposed of - Answer: return to approved recycling facility how would a technician check a three phase blower motor to determine that it is rotating in the proper direction - Answer: start the motor briefly using the disconnect to verify proper rotation hard start kits are typically required on - Answer: systems with reciprocating compressors and TXV metering devices a duct 36"x24" with an average of 600fpm is handling what cfm - Answer: 3600 a system is supplied with a factory charge of 5 pounds 10 oz for a 15 ft line set. and requires .6 oz per additonal foot. what is the total charge if the lineset needs to be 25ft in total. - Answer: 6lbs When performing a cycle check during a preventive maintenance call, the technician should:First, check with owner for equipment performanceNext, turn the unit off at the thermostat system switch then: - Answer: set fan switch to ON and check that the blower is running what is the recommended external static pressure used for heating and cooling equipment with blowers for 5 tons of cooling or less - Answer: .5 IWC The following conditions exist in a circuit that supplies power to three parallel loads.One load is resistiveOne load is capacitiveOne load is inductiveHow do you find the total current? - Answer: The sum of the currents through each load. What condition can cause a reduction from design capacity in a heat pump? - Answer: undersized suction line what is the purpose of the grounding conductor? - Answer: not sure, but i think personal and equipment protection what is the effect on supply airflow using a psc blower motor when adding a ducted return to a previously non ducted return - Answer: airflow will be increaded The airflow path of an outdoor unit pull through coil is air moves from the - Answer: outside to the inside. The blower wheel used by a direct drive blower will have an rpm that is: - Answer: the same as the blower motor. electronic type leak detectors typically have a push button or knob for setting a reference level, this is useful for - Answer: setting the detector for use in environments with ambient refrigerant vapor with the thermostat set to on which of the following measurements indicates a call for residential indoor blower operation - Answer: 24v at load side of relay **** not sure what effect does insuffiecnt voltage have on a solenoid valve - Answer: the valve will vibrate or chatter**** not sure according tot the generally accepted national code, what size should the condensate be. - Answer: 3/4" During a service call on a unit the technician finds that the wiring diagram is missing from the access panel. The technician may begin troubleshooting by: - Answer: Tracing the circuits either mentally or on a sketch pad what factors should a technician determine when replacing a contactor - Answer: coil voltage coil amp draw wire sizes and nmumber of poles what will refrigerant oil in a hose cause when a technician is checking the pressure in an operating system with manifold gauge - Answer: all readings will increase in value a delay on break relay delay load - Answer: from energizing for a fixed time after a cycle starts **not sure benefit of a media filter vs a fiberglass air filter - Answer: indoor air quality two 90 degree short radius elbows are added to an air conditioner suction line - Answer: there will never be an effect on the system performance cfm per ton of cooling - Answer: 350-450 cfm which mesures duct static pressure - Answer: anemometer what effect does overcharging have on sub cooling - Answer: increase sub cooling the continuity is checked through what measurement - Answer: ohms the purpose of a sequencer in an auxiliary 20kw electric heater is to energize - Answer: one or two elements and the blower motor simultaneously followed by remaining elements in timed intervals what would cause a voltage reading across a closed contact in a 24v control circuit - Answer: pitted or dirty contacts which of the following can casuse lower than normal suction pressure - Answer: a restriucted drier where should a technician check voltage to an energized compressor - Answer: at the load side of the compressor contactor ** not sure when a disc type close on rise pressure control is being used a s a loss of charge limit control on the liquid line has its setpoint drift lower - Answer: the system is less likley to shut down as a result of a small leak supply ducts running through unconditioned spaces should be insulated and have - Answer: vapopr barrier