Refrigeration Flashcards
Specific Heat Capacity
Is the amount of heat added or released to change the temperature of one pound of a substance by 1 degree F.
Superheat
Is the difference in temperature between a vapor and its condensation point
Calculate superheat temperature
Subtract its measured temperature from its condensation point temperature
Supercool
It measures the difference between a liquid and its boiling point
Ton to Btu/hr conversion
1 ton = 12,000 Btu/hr
Liquid Reciever
A storage tank for liquid refrigerant located on the high side between the condenser and the liquid line.
Liquid line
Tubing that carries liquid refrigerant from the condenser or liquid receiver to the metering device. (Smaller OD than suction line)
Metering Device
Located between the liquid line and the evaporator, its function is to lower the pressure of the refrigerant by restricting the passageway into the evaporator.
Accumulator
A tank in the suction line that prevents liquid refrigerant from flowing through the suction line and into the compressor.
Suction line
Tubing that carries refrigerant vapor from the evaporator to compressor. It should slope from the evaporator down to the compressor.
What is the nominal size for ACR tubing versus plumbing pipe?
Plumbing tube is equal to the OD minus 1/8”.
ACT tubing is designated by the actual OD.
Minimum radius for a 90 degree bend in copper tubing?
5 x Tubing OD
Why is the temperature that differentiates between solder and brazing?
If the temperature required to melt the filler alloy is:
- below 840F it is soldering
- above 840F it is brazing
Most flares on ACR tubing are made at an angle of _______
45 degrees
Capillary action
The movement of a liquid substance between two solid substances due to the molecular adhesive forces between the solids overcoming the liquid’s cohesive forces.
Fines are assessed up to _____ per day for failure to comply with the Clean Air Act.
$37,500 per day
Ozone Depletion Potential
The measurement of the ability of a refrigerant to destroy the ozone layer.
Global Warming Potential
Measure of the ability of a gas to contribute to global warming over time
A technician must be certified to what prior to performing refrigeration work?
Section 608 of the Clean Air Act
Class A refrigerants are NOT known to be toxic at concentrations equal or below _____
400 ppm
Class B refrigerants are those that ARE known to be toxic at concentrations equal to or below _____
400 ppm
Flammability classification
1 : No flammability
2 or 2L: low flammability
3: high flammability
Open motors are designed to operate at a given temperature rise as indicated on the motor nameplate. What does this mean?
It indicates the temperature rise over the surrounding air is operating at full-load conditions.
A low pressure control and high pressure control is usually located on the:
Condensing unit
The “term” nominal voltage refers to the:
Listed voltage
What is the purpose of the holding circuit in a magnetic motor starter?
Holds the main contacts closed until the control circuit through the interlock is broken
What is the density of untreated water?
8.33 pounds per gallon
Convert psig to psia
Psig + 14.7 = psia
What is effective voltage (Vrms)?
Vrms = Vmax x 0.707
Inductance
An electrical property that opposes a change in current
Power Factor
The relationship between a circuit’s true power and apparent power.
PF = (True Power (a wattmeter reading)/ Apparent Power ( calculated power in volt-amperes) x 100 = ___%
Section 440.14!of the NEC requires that a disconnecting men’s be readily accessible and within sight of HVACR equipment. The disconnecting means a can not be more than __ away from the unit.
50 feet and cannot require ladder use, tools or moving obstacles out of the way.
Out of the following control settings (set point, range, differential, cut-in) which is typically non-adjustable?
Range
The run capacitor on a motor is used to:
Increase torque
Fuses are sized by:
Both amperage and voltage
1 HP = _____ watts
746
When the temperature of a negative temperature coefficient material increases, it’s resistance will:
Decrease
BTU to Kw conversion
KW = BTUhr/3412.142
1 HP is equal to lifting _____ ft-lb per minute.
33,000
The voltage to the motor should not be less than ____ % of the rated voltage.
90%
1 ton of air = _____CFM
400
A motor is a____ load.
Inductive:
An inductive load pulls a large amount of current when first energized, then settles down to a full-load running current after a few seconds or cycles. When switched, inductive loads can cause excessive voltages. Some examples of inductive loads include transformers, motors and wound control gear
When replacing a motor what is the comparible current rule.
The replacement motor can never have a current draw less than the motor being replaced, but it may have a current draw that is 10% greater.
What is the millivolt reading of a good thermocouple?
15 mv
During replacement, if a different capacitance value must be used, a capacitance value up to___
10% greater that the original value can be used.
How do you test if a capacitor is good?
Place an ohmmeter across both terminals. Set the range switch for the ohmeter to a high setting (x100). If the meter swings toward zero and then slowly returns to infinity, the capacitor is good.
