Superheat And Subcooling

Question 1

If you have low superheat around 0-3 psi, why would that not be ideal?

Answer 1

Cause a low superheat is a indication that the refrigerant isn’t changing states and could have liquid going to the compressor instead of a vapor

Question 2

In a condenser coil what’s happening to the refrigerant?

Answer 2

The compressor raises pressure of vapor and then it travels through the coil and by the time it hits the liquidline it changed states to a liquid

Question 3

In a evaporator what’s happening to the refrigerant?

Answer 3

The refrigerant comes in 80% liquid and 20% vapor and then travels through the coil in its saturated temp without losing temp and then it exits a vapor

Question 4

If your system has a TXV how would you check pressures?

Answer 4

Subcooling and look on the nameplate to get desired cooling usually around 10

Question 5

If your system has a txv what should the superheat be between?

Answer 5

8-14degrees

Question 6

How would you find your current superheat on the unit?

Answer 6

Vapor line temp - saturated temp low side= superheat

Question 7

How would you find subcooling on a unit?

Answer 7

Saturated high side temp - liquid line temp= subcooling

Question 8

How long should you let the unit run with your guages attached to see pressures?

Answer 8

5-8 minutes

Question 9

A low or zero superheat means what?

Answer 9

That the refrigerant did not pick up enough heat in the evaporator coil to completely boil into a vapor
*bad for the compressor

Question 10

Excessive or high superheat is a indication of what?

Answer 10

Not enough refrigerant is entering the evaporator coil or excessive amount of heat load on evaporator coil

Question 11

A low subcooling is a indication of what?
And what causes low subcooling?

Answer 11

Not enough refrigerant is contained or packed in condenser

This can be due to undercharge, poor compression, or a metering device oversized or failing open (overfeeding).

Question 12

A HIGH subcooling is a indication of what?

Answer 12

That the unit is overcharged or refrigerant is backed up in the condenser

Question 13

If a evaporator coil is frozen what could be the causes?

Answer 13

Dirty filer, dirty fan motor, dead cap for fan motor, low charge

Question 14

What is superheat?

Answer 14

The temperature increase of vapor refrigerant

Question 15

How does a txv work?

Answer 15

A txv protects the compressor by maintaining a superheat of 8-14 degrees. The more heat the sensing bulb feels the wider the txv opens

Question 16

What are three ways you can test a txv?

Answer 16

1.)If it’s not opening up put bulb in your hand to warm it up or put it in hot water
2.) if it’s over feeding but bulb in cold ice water to close it
3.) add half a pound of refrigerant. If your suction does not rise and your head pressure does your txv is restricted.