Test #1

Test #1

To keep things interesting, I have decided to, on occasion, post system scenarios and give you guys the opportunity to evaluate the system and post possible causes for failure and repair otions.

Here is the first.

You have an air conditioning system that is operating with R-22 as its refrigerant and is equipped with a fixed bore metering device. The operating conditions are as follows:

Low side pressure: 26 psig

High side pressure: 156 psig

Outside ambient temperature: 85 degrees F

Evaporator outlet temperature: 54 degrees F

Condenser outlet temperature: 85 degrees F

Compressor discharge temperature: 250 degrees F

Return air temperature: 82 degrees F

Supply air temperature: 77 degrees F



You make the call.

One question

What will happen if there is insufficient airflow through the evaporator coil? Will the temperature split go up or down? Hmmmmmmmmmm

Evaporator Temperature Split

Correct.

If the airflow through an evaporator is decreased, the delta-t across the coil will increase and the evaporator saturation temperature and pressure will decrease. In this case, the evaporator saturation pressure and temperature are lower than normal and the temperature split across the evaporator is also low.

Let's clarify that the airflow through both the evaporator and condenser is correct.

Ding! Ding! Ding!

Either a blocked/restricted liquid line filter drier or a clogged/blocked capillary tube will result in the conditions provided.

Since the refrigerant cannot flow into or through the metering device, the refrigerant backs up in the condenser and reaches a temperature equal to the outside ambient temperature, giving us zero subcooling.

In addition, the amount of refrigerant being introduced to the evaporator is greatly reduced, so it boils very fast in the coil. This results in excessively high superheat.

Since the superheat is very high, a great deal of the coil is filled with vapor refrigerant, not liquid. Since more heat is transferred during a latent heat process (boiling or condensing), the amount ofheat absorbrd by the evaporator is reduced since the small amount of liquid refrigerant boils quickly at the inlet of the coil. The remainder of the coil facilitates a sensible heat transfer, as the temperature of the vapr refrigerant is increased. This reults in a lower delta-t across the evaporator coil.

Thanks for playing, guys. You can all be correct.

And yes, Tom, a restricted liquid line drie will have a temperature (and pressure) drop across it.

See you tomorrow with Test #2.