CONTROLS Flashcards
Because most induction motors require additional starting torque _________ are implemented.
Start windings
Shaded-pole motors can most easily be identified by
A heavy copper band
The primary application for shaded-pole motors would be
When low start torque is required
When low run torque is required
One of the most popular motors used in the HVAC industry with moderate starting torque and good running efficiency is the _________ motor.
Permanent split capacitor
Identify the most rugged and reliable motor used in the industry which operates without the assistance of start components
Three phase-motor
Identify the difference between a three pole contactor and a three pole magnetic starter
A magnetic starter has an overload circuit
In identifying the common, start, run terminals of a split phase motor; terminal A to B = 10 ohms, terminal A to C = 3 ohms, and terminal B to C = 7 which terminal is common
Terminal C
Electronically commutated motors alter the output drive speed. This is accomplished by altering
Electrical frequency
To safely test a motor capacitor a technician should
Discharge the capacitor with a resistor
If a compressor with an internal motor overload opens, what should the technician do before condemning the compressor
Allow the compressor to cool down
An air conditioning system uses a 24 volt control thermostat to maintain room temperature. The same system also utilizes a low pressure switch.
What is the most likely purpose of this low pressure switch?
To cycle the compressor off if the system runs low on
charge
A roof top air conditioning system with a defective condenser fan motor would be protected by
A high pressure safety cut out switch
A roof top air conditioner operating with a pressure type fan control maintains a minimum head pressure
During low ambient conditions
When adding central air conditioning to an existing heating system a fan relay center control (or fan relay) may need to be added, this relay would be controlled by which thermostat lead?
G- Green
To prevent room temperature “overshoot” most HVAC room thermostats employ a
Heat anticipator
Solenoid valves are
Magnetically controlled
A potential magnetic relay is controlled by the back electromotive force created by
The start winding
After a defrost timer control initiates a defrost period the defrost cycle may terminate by means of
Time, pressure, or temperature
A solid state starting relay is employed with fractional horse power compressors. after the motor starts the relay
Increases in resistance disconnecting the start winding
When troubleshooting a capacitor-start-capacitor- run motor and the technician finds the start capacitor and the run capacitor defective the technician must also check the operation of
Potential magnetic relay
Most low voltage HVAC room thermostats can adjust temperature over shooting, this adjustment would be a function of
Heat anticipator
A current sensing lockout relay is an overload device that senses the current draw of the compressor through the ______________
Lockout loop
When diagnosing the compressor contactor coil a proper resistance reading would be
45 OHMS
The best method to test the condition of the contacts in a compressor contactor would be
Visual inspection
