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15 Cards in this Set
- Front
- Back
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What do capacitors do when applied to AC voltage?
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They change the AC sine wave and cause the current to lead the voltage.
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Define a class 2 transformer.
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A class 2 transformer is an energy limiting transformer that limits the VA output and also the secondary VAC. Typically under 100 VA and no more than 30 VAC on the secondary but usually 75 VA and 24 VAC.
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What are the H terminals on a transformer?
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The H terminals designate the HIGHER VOLTAGE WINDING. This may or may not be the primary winding depending on wether it is a step up or step down transformer. Therefore the LOWER VOLTAGE winding will be designated with an X terminal.
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Inductors (oppose/attract?) a change of current and capacitors (oppose/attract?) a change of voltage.
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they both oppose.
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In a pure inductive circuit the current (lags/leads?) the applied voltage by ___°, and in a pure capacitive circuit the current (leads/lags?) the applied voltage by ___°
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An inductive circuit lags the applied voltage by 90 degrees. A capacitive circuit leads the applied voltage by 90 degrees.
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Three factors that determine the capacitance of a capacitor are:
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1. The area of the plates
2. The distance between the plates 3. The type of dielectric used |
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What are the 3 compressor types and which one are serviceable?
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1. Hermetic - Fully sealed and welded shut. Not servicable.
2. Semi-hermetic - Compressor and motor in a single shell and is servicable. 3. Open - An external motor that powers the servicable compressor through the use of a sealed crankshaft. |
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Where on the PE chart will you find the greatest change in enthalpy?
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From the compressor outlet to the metering device inlet. Most, but not all of it happens in the condenser and the term used is total heat of rejection.
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Where is the hottest point on the PE chart? The coldest.
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The outlet of the compressor.
The outlet of the metering device. |
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What is NRE?
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Net refrigeration effect is the difference in enthalpy that takes place inside the evaporator. Most of it is saturated and does not change temperature but some is superheated vapour and is still considered useful.
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What 5 measurements are needed to plot on the PE chart?
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1. High side pressure converted to PSIA (PSIG + 14.7)
2. Low side pressure converted to PSIA (PSIG + 14.7) 3. Temperature at the metering device inlet in F. (Subcooled liquid) 4. Temperature at evaporator outlet in F. (Superheated vapour) 5. Temperature at compressor inlet in F. (Superheated vapour) |
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What 2 factors determine the speed of a motor?
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Frequency and number of stator poles.
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What kind of rotor does the shaded pole motor use?
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Squirell cage.
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Where does an oil pump get its power from?
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It is connected to the end of the crankcase.
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As temperature increases resistance increases. What is this called?
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Positive temperature coefficient. PTC.
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