Unit 41 Troubleshooting Objectives Flashcards
What should you use before checking a capacitor with an ohmmeter?
You short the capacitor terminals with a 20000 ohm resistor.
What are the two most common refrigerants used in air conditioning today?
R-22 and R410A
What is the approach temperature?
known as temperature split. It is the difference in temperature between heat exchange mediums. Example would be the temp difference between the indoor coil and the return air for an AC system.
What is temperature difference?
It is the difference between inlet and outlet temperatures of the SAME medium. Example would be the temperature between air entering an evaporator and air leaving it.
What is a schrader valve?
It is a pressure connection that allows a technician to connect gauges to a system while keeping the refrigerant in the system
What is a service valve?
It is a valve that can be used to isolate the system for service. It is usually manually operated.
Why should you use a short gauge hose on the high side?
If you used a long hose, the amount of liquid refrigerant in the hose may be enough to affect the system charge and gauge readings.
What is the difference between wet bulb and dry bulb temperatures?
Wet bulb temps are taken with a spinning thermometer that has a saturated sock with pure water. It is used to evaluate the humidity in the air. Dry bulb temperatures is the normal temperature that measures the sensible heat in the air.
What is the difference between wet bulb and dry bulb temperatures?
Wet bulb temps are taken with a spinning thermometer that has a saturated sock with pure water. It is used to evaluate the humidity in the air. Dry bulb temperatures is the normal temperature that measures the sensible heat in the air.
When the dry bulb temperature and wet bulb temperature are the same, what is the humidity?
100%
What should be the highest discharge line temperature
It should not exceed 220°F.
What situations can cause high compression ratios?
They can result from low suction pressures, high condensing pressures, or combination of both.
At the condensing unit, what should be the typical superheat and subcooling ranges?
Superheat should have 10-20°F more than evaporator pressure/temperature. Subcooling should have 10-20°F less than condenser pressure temperature.
At the evaporator, what should be the typical superheat?
Superheat at the evaporator should have 8-12°F more than evaporator pressure/temperature.
What is the standard Delta T between return and supply air?
Delta T should be 18-22°F.
Why do the suction and liquid lines have different diameters?
The refrigerant in the suction line is in a vapor state and would not be able to hold as much refrigerant if it was the same diameter as the liquid line.
If a system has a TXV and the superheat is extremely low, what may be the cause?
Check the sensing bulb and make sure that it is attached and insulated. If it is not, this can cause the TXV to be wide open to try to lower the sensing bulb temperature. This causes the evaporator to be flooded.
When beginning electrical troubleshooting, what should be your first step?
Verify that that power supply is energized and that the voltage is correct.
For a normal operating compressor, how should it feel?
A normal compressor should feel very warm to hot. If it is too hot to touch, then there is a problem with the compressor.
T or F - If a compressor is not working and very hot to the touch, you should wait for it to cool down before condemning it?
True- the internal compressor overload protector may have tripped due to a problem such as a low charge. Let it cool and see if starts working again.
T or F - You can use your ohmmeter to check a live circuit?
False- never use an ohmmeter to check a live circuit. It can damage the meter.
What terminal is the thermal overload switch connected to?
It is connected to the common terminal.
If the thermal overload switch is open, will you read any resistance between the Start - Run terminals? How about Run - Common? Start - Common?
For Start - Run, you would read normal resistance if the only problem is an open thermal overload switch. For both Run - Common and Start Common you would not read any resistance but get OL.
T or F - You get the same resistance across each motor winding in a three-phase motor.
True
If no crankcase heat is at the compressor, what may happen to the refrigerant charge?
The charge may migrate to the crankcase.
If a condenser circuit breaker is tripped, what should you do?
A. Reset it
B. Check the suction pressure
C. Check the high-side pressure
D. Perform a resistance check of the compressor section
D. Perform resistance check of the compressor section. Take the motor leads off the compressor and check for a ground circuit in the compressor.
Two necessary tools to diagnose a system
Quality digital thermometer and gauge manifold
Elisondro do cards
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