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Air Conditioning Charging Procedures Review

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Air Conditioning Charging Procedures Review. Basic Refrigeration. Basic Refrigeration. Liquid Line. Liquid Line. Metering Device. Condenser. Low Side. Hi Side. Evaporator. Compressor. Saturation Temperature. What is Saturation Temperature?.

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Air Conditioning

Charging Procedures


basic refrigeration1
Basic Refrigeration

Liquid Line

Liquid Line




Low Side

Hi Side





what is saturation temperature
What is Saturation Temperature?
  • Saturation temperature is the actual temperature of the evaporator and condenser coils….
  • In saturation conditions, both vapor and liquid are present
how do you find saturation temperature
How do you find Saturation Temperature?
  • Refrigeration Gauges
  • The Only purpose of owning a set of gauges is to find the refrigerant saturation temperature….
saturated refrigerant
Saturated Refrigerant

Liquid Line





Discharge Line

Suction Line


first things first

First things first…

You must verify that you have proper airflow!…and you must have the proper tools to do the job….

air flow measurements
Air Flow Measurements
  • Total Static Pressure
  • CFM Measurements:

-Temperature Rise

-Evaporator Pressure Drop

-Air – Velocity

-Temperature Drop*

static pressure measurement
Static Pressure Measurement
  • The key to system airflow diagnostics
  • A companion to airflow measurement
  • It takes less than 5 minutes to measure
  • Similar to blood pressure diagnostics
cfm by temperature rise
CFM By Temperature Rise


T X 1.08*


*1.08 = constant number for std air. It’s a combination of a number of values that are in the complete equation. Std air is 70F, sea level

cfm by temperature rise1
CFM By Temperature Rise

55,200 BTU output

60 X 1.08

=850 CFM


  • Velocity = FPM
  • CFM= FPM X Area in Square Feet
  • Free Area
Humid Air

Dry Air

fan speed taps
Fan Speed Taps
  • Check Service Facts for proper air speed tap to use
  • Match tap to size (BTUH) of unit
the right stuff

The Right Stuff:

Basic Tools:

Refrigerant Gauges

Digital Thermometer (one with Wet Bulb capabilities)

system charging
  • The sub-cooling method is required when charging TXV systems.
  • The super-heat method is required when charging fixed orifice systems.
  • Charging charts are included in the Service Facts document that come with the outdoor equipment.
  • Remember to allow sufficient time for the system to stabilize before adjusting the refrigerant charge.
system charging sc using the charging chart txv
SYSTEM CHARGING(SC)Using the Charging Chart-TXV
  • Measure temperature and pressure at liquid line.
  • Use line length & lift to choose which curve to use.
  • Plot the intersection of temp. & pressure.
  • If above the curve, remove refrigerant.
  • If below, add refrigerant
  • Wait 20 minutes to stabilize.
sub cooling calculation
Sub-Cooling Calculation
  • Low Sub-Cooling indicates LOW charge
  • High Sub-Cooling indicates OVER charge ( or possible liquid line restriction)
  • Rule of thumb = 10 - 15 degrees of sub-cooling Manufactures’ usually design to 10 degrees
system charging sh using the charging chart fixed orifice
SYSTEM CHARGING(SH)Using the Charging Chart-Fixed Orifice
  • Measure indoor dry bulb* (R/A)
  • Measure outdoor dry bulb (at unit)
  • Measure suction pressure
  • Measure suction temperature, before suction service valve
  • Use chart to determine SH
  • Above 5 F above, add. If 5 F below, remove.
  • If below 5 F limit line, DO NOT ADD.
  • *If RH >70% or <20%, use ID wet-bulb
superheat calculation
Superheat Calculation
  • Superheat indicates that complete vaporization of liquid refrigerant in the evaporator coil has taken place
  • Low Superheat means liquid refrigerant is present at or near the outlet of the evaporator - compressor damage is immanent
  • High Superheat means liquid is boiling off too soon and could mean evaporator is starved
customer complaint
Customer Complaint:
  • “System does not cool like it before when it was new…”
  • What do you do?

+ “Check the Enthalpy of the Evaporator Coil to verify system capacity…”

use the formula
Use the Formula:

Total Heat Removed =

CFM X 4.5 X Change inEnthalpy (Heat Content)

  • Same as TOTAL HEAT
  • The sum of sensible heat and latent heat

Where’s the 4.5 come from?

It’s how many BTU’s are in one pound of DRY air (0%Rh)

Total Heat =CFM X 4.5 X Enthalpy Change

69 WB=33.25

60 WB=26.46

Difference = 6.79

800 X 4.5 X 6.79

= 24,444 BTUH !