Transcript AC Charging Procedur..

Air Conditioning
Charging Procedures
Review
Basic Refrigeration
Basic Refrigeration
Liquid Line
Liquid Line
Metering
Device
Condenser
Hi Side
Low Side
Evaporator
Compressor
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?
• Refrigeration Gauges
• The Only purpose of owning a
set of gauges is to find the
refrigerant saturation
temperature….
Saturated Refrigerant
Liquid Line
Condenser
Metering
Device
Evaporator
Discharge Line
Compressor
Suction Line
First things first…
You must verify that you
have proper airflow!…and
you must have the proper
tools to do the job….
Air Flow
Air Flow Measurements
• Total Static Pressure
• CFM Measurements:
-Temperature Rise
-Evaporator Pressure Drop
-Air – Velocity
-Temperature Drop*
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
Total Static Pressure
Air Flow MeasurementTemperature Rise Method
to determine CFM
Airflow Measurement
(Temperature Rise Method)
(Red Book, Pg. 33)
CFM By Temperature Rise
BTUH OUTPUT
T X 1.08*
= CFM
*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 Rise
55,200 BTU output
60 X 1.08
64.8
= 850 CFM
CFM
By Evaporator
Pressure Drop
Velocity
• Velocity = FPM
• CFM= FPM X Area in Square Feet
• Free Area
Humid Air
Dry Air
Fan Speed Taps
• Check Service Facts for proper air
speed tap to use
• Match tap to size (BTUH) of unit
Blower should always be on high speed?
•2 TON – 800 CFM
The Right Stuff:
Basic Tools:
1. Refrigerant Gauges
2. 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.
Beer Can Cold and
Sweaty
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
• 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
(390 PSIG & 115º F)
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 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:
• “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:
Total Heat Removed =
CFM X 4.5 X Change in Enthalpy (Heat
Content)
Enthalpy
•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 !