A/C troubleshooting / symptoms

Question 1

What could cause high superheat?

4

Answer 1

• starving txv
• restricted orfice tube
• restricted receiver dryer
• low charge

Question 2

What could cause low superheat?

Answer 2

flooding txv or orfice tube

Question 3

What could cause high subcooling?

4

Answer 3

• excess charge
• low ambient air temperature
• air flow through the condenser is high
• restricted receiver dryer

Question 4

What could cause low subcooling?

3

Answer 4

• low charge
• flooding txv
• restricted flow through the condenser

Question 5

A failing compressor will show up as?

TQ / IP question

Answer 5

A low pressure on the high side and a high pressure on the low side.

Question 6

What kind of subcooling should you see at the condenser?

Answer 6

10-20*F

All systems

Question 7

What kind of superheat should you see at the evaporator?

Answer 7

6-12*F on txv systems

0-4*F on orfice tube systems

Question 8

What should the static high side pressure be?

Answer 8

2 - 2.5x the ambient air temperature

Question 9

On a clutch cycling system, what should the static low side pressure be?

Answer 9

15-30 psi on txv systems

20-45 psi on orfice tube systems

Question 10

On a variable displacement system, what should the static low side pressure be?

Answer 10

29psi + or - 1psi (28-30psi)

txv and orfice tube

Question 11

Low side pressure lower than normal could be caused by:

2

Answer 11

• insufficient refrigerant entering the evaporator

- too much refrigerant is being removed from the evaporator

Question 12

Low side pressure higher than normal could be caused by:

2

Answer 12

• excessive refrigerant entering the evaporator

- not enough refrigerant is being removed from the evaporator

Question 13

Symptoms of a low refrigerant charge:

5

Answer 13

• low side pressure lower than normal, may indicate a vacuum
• high side pressure lower than normal
• higher than normal superheat
• lower than normal sub-cooling
• outlet duct temperature warmer than normal

Question 14

Symptoms of air in the system:

6

Answer 14

• low side pressure normal to higher than normal
• high side pressure higher than normal, may be very high depending on the amount of non-condensable gas
• normal to slightly higher superheat
• lower than normal sub-cooling
• outlet duct temperature warmer than normal
• when checking static gauge pressure, you may see higher than normal ambient pressures

Question 15

Symptoms of excessive refrigerant charge:

5

Answer 15

• low side pressure normal to higher than normal
• high side pressure higher than normal
• normal superheat
• higher than normal sub-cooling
• outlet duct temperature warmer than normal

Question 16

Symptoms of moisture in the system:

5

Answer 16

• low side pressure normal to lower than normal
• high side pressure normal then drops below normal after extended operation
• normal superheat at first then becomes excessive after extended operation
• normal to higher than normal sub-cooling
• outlet duct temperatures normal at first then becomes warmer after extended operation

Question 17

When testing an A/C system, if you cant get the compressor to cycle off, what can you do to manipulate the system?

Answer 17

lower the fan speed to lower the heat load

Question 18

If both static pressures are lower than the corresponding pressure/temperature chart, what could be the cause?

Answer 18

its probably a low charge

Question 19

What would cause both static pressures to be around 20psi higher than normal?

Answer 19

an azeotrope

Question 20

What is static pressure?

Answer 20

gauges hooked up but the system is not running