1. R4 Troubleshooting Refrigeration
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
R4 Troubleshooting Refrigeration
#3 Enthalpy, Dirty Condensers, Subcooling
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

2. R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Enthalpy
“The amount of heat a substance contains, determined from some base.”
Enthalpy diagrams show:
Btu per pound of refrigerant
At a certain:
Pressure
Temperature
State (% vapor or liquid)
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

3. “Approximate” R22 Pressure/Enthalpy Diagram
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
-40o
-20o 0o
20o
60o
80o
160o
200o
220o
230o
180o
140o
120o
100o
40o
PRESSURE
Sat. Liquid
Sat. Vapor
340 #
260 #
69 #
The enthalpy diagram above represents an approximate diagram for R22.
It may not be exact, but it is close enough for the instructional purposes we intend. 0%
100%
% Vapor
ENTHALPY(HEAT) in BTU/Pound
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

4. Temperature, Pressure, & State
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Temperature, Pressure, & State
The following diagram shows how:
Refrigerant temperature,
Pressure,
And state (vapor or liquid)
change as it goes through the system.
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

5. Changing Pressure, temperature, and state of refrigerant
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Example: Standard A/C 90° Ambient & 75° return temp.
Note: No superheat and no sub-cooling
230o
Liquid Temp is Condensing Temp
90˚ Amb + 30˚ = 120˚
220o
220o
Cooled to 120˚, Hot Gas starts to condense
200o
200o
180o
180o
Sat. Liquid
160o
Sat. Vapor
160o
Gas enters condenser
Enters metering device
140o
Condensing
140o
185o
260 #
120o
120o
120o B A
Compression
185˚ Hot Gas discharged from compressor
100o
Pressure/Temp drop through metering device
100o
Evap. Temp
80o
80o
60o
Evaporating
60o
69 #
This slide helps to show what happens as refrigerant changes states from liquid to vapor under both high and low pressure situations.
There is no provision for superheat or subcooling. Those factors are introduced later.
40o
40o
Enters compressor (no superheat)
20o
Enters 33% Vapor & 67% Liquid
“Adiabatic Expansion”
20o 0o 0o
-20o
-20o
PRESSURE 0%
100%
-40o
% Vapor
-40o
ENTHALPY(HEAT)
65 BTU/lb
20 BTU/lb
Heat of Compression
Refrigeration Effect
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

6. R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Dirty condenser
The following slide shows how a dirty condenser decreases system efficiency.
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

7. Effects of a Dirty Condenser on Enthalpy
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Example: Standard A/C 90° Ambient & 75° return temp.
Note: No superheat and no sub-cooling
but DIRTY CONDENSER
230o
Cooled to 140˚ Hot Gas starts to condense
Dirty coils require higher pressure & temperature to reject heat
220o
220o
200o
200o
180o
180o
Gas enters condenser
Enters metering device
Sat. Liquid
160o
160o
Condensing
Sat. Vapor
200o
340 #
140o
140o
140o B A
Compression
200˚ Hot Gas discharged from compressor
260 #
120o
Higher Pressure/Temp drop through metering device
120o
100o
100o
Evap. Temp
80o
80o
60o
60o
69 #
All techs know systems do not operate well if they have a dirty condenser.
However, this slide shows why, and how much.
40o
40o
Enters 35% Vapor & 65% Liquid (less efficient)
Evaporation
Enters compressor (no superheat)
20o
20o 0o 0o
-20o
-20o
PRESSURE 0%
100%
-40o
% Vapor
-40o
Only 60 BTU/lb
ENTHALPY(HEAT)
Refrigeration Effect
8% Capacity Loss
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

8. R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Subcooling
The following slide shows how subcooling increases system efficiency.
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

9. The Benefits of Subcooling
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
Example: Standard A/C 90° Ambient & 75° return temp.
Note: No superheat and no sub-cooling
Add 10° sub-cooling and 10° superheat
230o
220o
220o
Cooled to 120˚, Hot Gas starts to condense
200o
200o
Liquid Sub-Cooled 10° from 120° to 110°
180o
180o
Sat. Liquid
Gas enters condenser
160o
Sat. Vapor
160o
140o
Condensing
140o E
190o
260 #
120o
120o
120o
190˚ Hot Gas discharged A
Compression
100o
Metering
100o
Evap. Temp
80o
80o
60o
60o
Evaporation B C
69 #
We only use suction superheat as a safety to prevent compressor flooding. As the slide shows, it doesn’t do much for overall performance.
Subcooling, on the other hand, is very beneficial to the efficiency of the system.
This slide shows that fact quite clearly.
40o
40o
50o
25% vapor–75% liquid D
10° Superheat added
20o
20o 0o
Less vapor to cool means more liquid to refrigerate 0o
-20o
-20o
PRESSURE 0%
100%
-40o
% Vapor
-40o
ENTHALPY(HEAT)
Increase to 70 BTU/lb
2 BTU/lb Sensible Heat
8% Capacity Gain
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

10. End of Enthalpy 1/11/2019 © 2004 Refrigeration Training Services
R4 Troubleshooting Refrigeration - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.1
1/11/2019
End of
Enthalpy
© 2004 Refrigeration Training Services R4 - Subject 3 Enthalpy, Dirty Condensers, Subcooling v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed