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67 Cards in this Set
- Front
- Back
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The difference in temperature between two mediums |
Approach temperature |
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Standard approach temp for ac is? |
35F |
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Approach is used to determine |
The condition of the condenser / heat exchanger |
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A high approach could indicate? |
The condenser is not condensing efficiently - not enough air flow |
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Inlet versus outlet temperatures of the same medium are called |
DELTA T |
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Measure between two mediums? One medium? |
Approach Approach Delta T Delta T |
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Condensing temperature should be no more than 15 Degrees above? |
Ambient temperature |
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75F return at 50% humidity is known as |
Standard air |
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Standard efficiency systems boil at what temperature below entering air |
35F |
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More than normal condensate from an AC system could indicate? |
High moisture content in the air |
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Standard condensing temperatures are? High efficiency are? |
30F 15F |
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Low charge or refrigerant restriction could indicate |
High superheat |
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If suction pressure is low and suction line is warm what could this mean? |
Starved evaporator |
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If suction line temp is low and boiling at low temps this could indicate? |
Airflow issue |
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What does r22 boil at? 410a? |
-44 -55 |
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If filters are plugged what symptoms on the low side might you see |
Suction gas may be part liquid Suction line will be excessively cold Compressor may bet sweating |
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Low suction pressure is low but super heat is very high this could indicate? |
Low charge |
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When suction pressure is low and super heat is low this could indicate? |
Flooded coil |
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Discharge line temps are indication of |
Compressor operation |
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What would be an indication of an Internal leak from high to low side? |
Rising discharge temp |
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Maximum discharge line temperature? |
220F |
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If the suction line heats up quickly after shutting the unit off what could this be an indication of? |
Internal leak between discharge and suction |
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High compression ratios will provide what kind of discharge temperatures? |
High discharge temperatures |
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The result of high condensing pressures and low auctions pressures could indicate? |
High compression ratios |
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High super heats will increase what on the high side? |
High discharge temps |
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High super heat and discharge temps could be a sign of? (3) |
Under charge Restricted filter Metering device starving system |
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Subcooling is checked from which line? |
Liquid line |
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Most condensers subcool between what temperatures? |
10-20F |
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Lower subcooling could indicate |
Low charge |
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Condensers perform 3 tasks? |
Removes superheat Condenses Subcools |
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The amount of refrigerant in an evaporator can be measure by? |
Superheat |
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Subcooling can measure the amount of refrigerant where? |
The condensee |
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If the evaporator is not performing correctly what can be said about the liquid line charge? |
The charge is incorrect |
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The length of the liquid line and amount refrigerant can determine? |
How much refrigerant is in the liquid line |
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The condenser will operate more efficiently when the ambient air is higher? True or false? |
False |
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In a cap tube system when refrigerant condenses faster due to lower ambient conditions - what effect does this have on the evaporator? |
Starve the evaporator |
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The highest condenser head pressure should be? |
30F above ambient |
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Correct superhear should range between |
8-15F |
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And average must be used to determine superheat with what type of metering device? Why? |
Cap tubes The hunt in normal operation |
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Standard operating head pressures for r22 and 410a at 95F ambient are? |
R 22 - 278 410 - 445 |
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Why is the superheat method on a txv system not as reliable as subcooling |
The valve maintains superheat regardless of charge |
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If subcooling is 20-25F above ambient what might this be a symptom of? |
Over charge |
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What is the first step in troubleshooting electrical faults |
Establish power! |
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By turning a fan on at the thermostat what can you ensure is happening if the fan starts (2) |
Control and line voltage are present Control and line voltage are presentFan relay works Fan relay works |
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If low voltage is present but the load does not energize on a call for heating or cooling what else might be good to check? |
The contactor |
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If the contactor is pulled in on a call for heating or cooling and you get high amperage with no pressure change what might this be an indication of |
LRA Short to ground /shorted winding Failed compressor |
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Reading between compressor contact and to ground what reading should you see? |
O.L |
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How can you test a txv valve |
Increase head pressure Or placing the bulb in a warm glass of water |
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If the compressor wont start and is too hot to touch what might this indicate? |
Tripped on internal overload |
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Low charge, and failed start assist, and overheating will cause a compressor to? |
Trip on overload |
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A megohmeter is used on smaller or larger systems exclusively? |
Larger systems |
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If you suspect a compressor has shorted to ground what will you read on your ohm meter? |
Resistance over 1 |
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If you suspect a compressor winding has shorted what reading will you read? |
O.L or continuity beep |
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Which winding will have more resistance - start ir run? |
Start |
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Voltage must be within how many percent for correct operation? |
10% |
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In a three phase motor what resistance should you read across each winding? |
The same resistance across each winding |
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A resolve for a three phase compressor not running correctly could be? |
Change any two leads |
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If voltage is correct but amperage is below RLA what can be said about compressor capactity |
Compressor is not pumping to capacity |
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A good sign in gauge pressure to determine poor compressor capacity would be? |
Suction is a little high Discharge is a bit low |
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When a breaker trips from a compressor overload what is the best thing to do? |
Ensure power is off Test resistances of the winding and to ground |
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A reversing valve with a failed open coil will result in ? |
No change over - stuck in which ever mode the system fails too |
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What are symptoms on a motor with a failed start device (capacitors) (3) |
Motor wont start High amps or LRA will be drawn Motor will over heat |
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Defective indoor txv (summer) can be recognized by |
Low suction pulling into a vac |
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Defective txv on the outdoor coil (winter) |
Low suction pulling vac |
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Pressures being closer together could indicate |
Poor compression ratio Compression efficiency down Capacity down |
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When diagnosing a heat pump which mode will you test in? |
Always in cooling |
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A measurement across a live closed switch would read? To ground |
0 volts Line volts |
