14 Flashcards
Surrounding air temperature
Ambient temperature
A control that has no connection to electrical power such as a TXV.
Mechanical controls
Normally regulates other controls and does not carry much current (2A max).
Low voltage thermostat
Detects presence of gas pressure in gas burning equipment before burners are allowed
to ignite.
Gas pressure switch
Detects excess pressure in any system that contains fluid.
Pressure relief valve
Bimetal formed into a shape like a cylindrical coil spring that provides longer travel when heated.
Helix coil
High- and low-pressure controls built in one housing.
Dual pressure control
Reduces gas transmission pressure to usable pressure at the burner.
Gas pressure regulator
Safety device used on boilers to release excess pressure.
Boiler relief valve
Keeps refrigerant from migrating to the oil during any long periods of off time.
Crankcase heat
Contains a small amount of mercury that makes or breaks the electrical circuit contacts in a low voltage thermostat.
Mercury bulb
Gas that will not support most chemical reactions, particularly oxidation.
Inert gas
Uses a large diaphragm to sense very low air pressure in air ducts to sense blower air before heat is activated.
Air pressure control
Thermistor or bimetal device that prevents motor from overheating.
Motor temperature cut-out
Converts mechanical energy to operate an electrical function.
Electromechanical controls
A central air conditioner is set to “Cool” but the system is not operating. You check the thermostat and see that the display is illuminated. You place the switch to the off position, wait a few minutes and then move the switch back to “Cool” and wait for the start delay to expire.
After 10 minutes, the unit still does not start. You pull the thermostat off the subbase to see if the wires are in the correct terminals. You observe that the red, green and yellow wires are in the correct terminals and the “C” terminal is not being used. The thermostat requires two AA batteries. The thermostat display is still illuminated.
You use your meter to check the batteries to see if they have the correct voltage. At what volt reading would you consider each battery to be no good?
Below 1.3 volts
The batteries are above the minimum voltage reading so you don’t need to change them.
You can do one more test to confirm if the thermostat is the cause of the system not starting by doing what? Explain in detail.
Check for voltage in each of the wires and the transformer
Immediately after you do the test above in question 17, you hear and feel the blower operating but when you go outside to check the compressor, only the condenser fan is operating and the compressor isn’t running. What is wrong?
Possible bad start components, bad compressor, internal overload tripped.
The high event on a thermostat or pressure control is also known as the cut-in point. T/F
T
Oil pump discharge pressure is 200 psig and the suction pressure is 120 psig. Net oil pressure is 320 psig. T/F
F
Non-condensables in a system will cause higher head pressure because it takes up
valuable volume in the condenser. T/F
T
A water regulating valve for a water-cooled condenser is a mechanical control. T/F
T
The pressure setting on a relief valve can be adjusted. T/F
F
Oxidized mercury in a bulb switch could cause the switch to always be in the
closed position. T/F
T
A broken condenser fan motor will cause a low-pressure control to shut the compressor off. T/F
F
Do not use water to cool a compressor housing made of cast iron. T/F
T
Brass or copper mounting straps should be used to secure sensing bulbs to the suction line where freezing temperatures occur. T/F
T
The thermometer indicates the temperature of the bulb at the end of the thermometer, not the temperature of the substance it is in contact with. T/F
T
To adjust the heat anticipator in a non-digital/electronic thermostat, measure the current between the R and Y terminals with a clamp meter when the heat circuit is energized. T/F
F
The cold anticipator shuts the compressor off a few degrees before the set point
temperature to allow for residual cooling to prevent overshoot. T/F
F
What is used in a non-digital/electronic thermostat to reduce system lag and how is it installed in the circuit of the thermostat?
A cold anticipator, in a parallel circuit.
If the internal overload on a compressor has functioned, how do you verify it with your
meter and what would your meter readings be?
Check C-R R-S C-S OL
A thermostat has a cut-in setting of 40°F and a cut-out setting of 35°F. The differential is set at 5°. What is the cut-out temperature if the differential remains the same, but the cut-in temp is increased to 45°F?
10°F
How long is the time delay in an oil pressure monitoring control to allow oil pressure to build up when a compressor first starts?
90 seconds
What is the best procedure to handle a hot compressor and you suspect the internal overload has functioned?
Turn it off let it cool and see if it resets.
