A pressure-time-temperature defrost system goes into defrost with ...

[RRMR]

A pressure-time-temperature defrost system goes into defrost with very little frost on the bottom of the coil. Describe the major cause of and solution to this problem.
 
  What will be an ideal response?

Question 2

Where are the specific enthalpy lines and how are they marked?
 
  What will be an ideal response?

[vickybb89]

Answer to Question 1

The major cause of this action is a dirty outdoor coil, which causes an increased air pressure drop across the outdoor coil. Cleaning the coil solves this problem.

Answer to Question 2

The specific enthalpy lines are vertical lines going from top to bottom; the scale is shown along the top and bottom of the PH diagram. The units are given in Btu per pound of refrigerant, Btu/lb.