Unit 41 Troubleshooting Objectives

Question 1

What should you use before checking a capacitor with an ohmmeter?

Answer 1

You short the capacitor terminals with a 20000 ohm resistor.

Question 2

What are the two most common refrigerants used in air conditioning today?

Answer 2

R-22 and R410A

Question 3

What is the approach temperature?

Answer 3

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.

Question 4

What is temperature difference?

Answer 4

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.

Question 5

What is a schrader valve?

Answer 5

It is a pressure connection that allows a technician to connect gauges to a system while keeping the refrigerant in the system

Question 6

What is a service valve?

Answer 6

It is a valve that can be used to isolate the system for service. It is usually manually operated.

Question 7

Why should you use a short gauge hose on the high side?

Answer 7

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.

Question 8

What is the difference between wet bulb and dry bulb temperatures?

Answer 8

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.

Question 9

What is the difference between wet bulb and dry bulb temperatures?

Answer 9

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.

Question 10

When the dry bulb temperature and wet bulb temperature are the same, what is the humidity?

Answer 10

100%

Question 11

What should be the highest discharge line temperature

Answer 11

It should not exceed 220°F.

Question 12

What situations can cause high compression ratios?

Answer 12

They can result from low suction pressures, high condensing pressures, or combination of both.

Question 13

At the condensing unit, what should be the typical superheat and subcooling ranges?

Answer 13

Superheat should have 10-20°F more than evaporator pressure/temperature. Subcooling should have 10-20°F less than condenser pressure temperature.

Question 14

At the evaporator, what should be the typical superheat?

Answer 14

Superheat at the evaporator should have 8-12°F more than evaporator pressure/temperature.

Question 15

What is the standard Delta T between return and supply air?

Answer 15

Delta T should be 18-22°F.

Question 16

Why do the suction and liquid lines have different diameters?

Answer 16

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.

Question 17

If a system has a TXV and the superheat is extremely low, what may be the cause?

Answer 17

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.

Question 18

When beginning electrical troubleshooting, what should be your first step?

Answer 18

Verify that that power supply is energized and that the voltage is correct.

Question 19

For a normal operating compressor, how should it feel?

Answer 19

A normal compressor should feel very warm to hot. If it is too hot to touch, then there is a problem with the compressor.

Question 20

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?

Answer 20

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.

Question 21

T or F - You can use your ohmmeter to check a live circuit?

Answer 21

False- never use an ohmmeter to check a live circuit. It can damage the meter.

Question 22

What terminal is the thermal overload switch connected to?

Answer 22

It is connected to the common terminal.

Question 23

If the thermal overload switch is open, will you read any resistance between the Start - Run terminals? How about Run - Common? Start - Common?

Answer 23

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.

Question 24

T or F - You get the same resistance across each motor winding in a three-phase motor.

Answer 24

True

Question 25

If no crankcase heat is at the compressor, what may happen to the refrigerant charge?

Answer 25

The charge may migrate to the crankcase.

Question 26

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

Answer 26

D. Perform resistance check of the compressor section. Take the motor leads off the compressor and check for a ground circuit in the compressor.

Question 27

Two necessary tools to diagnose a system

Answer 27

Quality digital thermometer and gauge manifold

Question 28

Elisondro do cards

Answer 28

Ok