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What is Superheat and Subcooling?
Why Do I Need to Measure It?
Superheat is the difference between the
actual temperature of the refrigerant (gas) as
it leaves the evaporator and the boiling point
of the refrigerant. After boiling, the refrigerant
continues to heat up. The number of degrees it
“heats up” after boiling is called the superheat.
Under worst case conditions (low load for fixed
orifice systems), the refrigerant in the evaporator
boils off near the end of the evaporator coil. To
make sure liquid doesn’t enter the compressor
under the worst case condition (low load),
the refrigerator or A/C manufacturers publish
charts indicating what the superheat should be
at a given indoor wet bulb measurement and
outdoor air temperature.
Measuring superheat is your best indication
on a fixed orifice system of the proper
refrigerant charge and operating conditions.
If everything else is working properly and the
actual superheat is too high, add refrigerant. If
it’s too low, evacuate refrigerant.
Subcooling is the difference between the
boiling point of the refrigerant in the condenser
and the actual temperature of the refrigerant
as it leaves the condenser. The degrees that the
refrigerant “cools down” below the boiling point
is the subcooling. Under worst case scenario
(low load for TXV) the subcooling will continue
to rise. If the subcooling rises too high, liquid
may be backed into the compressor causing
damage and catastrophic failure. See www.
fieldpiece.com for more technical articles.
Location of Subcooling Test
Location of Superheat Test
Specifications
Display size:
5 inches (diagonal)
Backlight:
Blue (On for 3 minute unless turned off manually)
Mini-USB Port:
For updating to latest version of firmware.
Battery:
6 x AA (Battery life below based on alkaline type)
Battery life:
350 hours (without backlight)
Low battery indication:
is displayed when the battery
voltage drops below the operating level
Auto Shut off:
30 minutes of inactivity when APO is activated
Operating environment:
32°F to 122°F (0°C to 50°C) at <75%
relative humidity
Storage temperature:
-4°F to 140°F (-20°C to 60°C), 0 to 80% RH
(with battery removed)
Temperature coefficient:
0.1 x (specified accuracy) per °C (0°C to
18°C, 28°C to 50°C), per 0.6°F (32°F to 64°F, 82°F to 122°F)
Over range:
"OL" or "-OL" is displayed
Weight:
3.04 lbs (1.38 kg)
Pressure
Connector Type:
Standard 1/4" NPT male flare fitting
Range:
29” HgV to 580 Psig (English), 74 cmHgV to 0 to 4000KPa
(Metric)
Resolution:
0.1 psi/inHg; 1 kPa/cmHg
Accuracy:
29” HgV to 0” HgV: ±0.2” HgV
74 cmHgV to 0 cmHgV: ±1 cmHgV
0 to 200 Psig: ±1 Psi; 0 to 1378 KPa: ±7 KPa; 0 to 1.378MPa:
±0.007MPa; 0 to 13.78 bar ±0.07 bar
200 to 580 Psig: ±(0.3% of 1 Psig); 1378 to 4000KPa: ±(0.3% of
7 Kpa); 1.378 to 4.000MPa: ±(0.3% of 0.007MPa);
13.78 to 40.00bar: ±(0.3% of r0.07bar)
Maximum overload pressure:
800 psig
Units:
Psig, kPa, MPa, bar, inHg, and cmHg
Temperature
Sensor type:
Type K thermocouple
Range:
-95°F to 999.9°F (-70°C to 537.0°C)
Resolution:
0.1°F/°C
Accuracy:
±(1.0°F) -95°F to 199.9°F; ±(0.5°C) -70°C to 93°C
±(2.0°F) 200°F to 999.9°F; ±(1.0°C) 93°C to 537.0°C
Note: All accuracies are after a field calibration.
Recommended
Accessory
Easy View Micron Gauge
Model SVG3
Measure the depth of the vacuum in microns
of mercury to verify all moisture and non-
condensibles have been removed from the
system. For the most accurate reading, connect
directly to a service port on the system or to a
Schrader core removal tool (illustrated below).
Calibration
Temperature
To calibrate your SMAN temperature
thermocouples, adjust the pot on the front
of the meter labeled SLT Cal or LLT Cal. The
best way to calibrate is to match to a known
temperature. Ice water is very close to 32°F and
is readily available. Accuracies of one degree or
better are easily obtained.
1 Stabilize a large cup of ice water by stirring. Pure, distilled water
will be the most accurate.
2 Immerse the temp probe in ice water from SLT and adjust the
SLT Cal pot with a flathead screwdriver and let it stabilize, keep
stirring.
3 Repeat Step 3 for temp probe in LLT.
Pressure Zeroing
To calibrate your SMAN340 pressure sensors
to atmospheric pressure, ensure that your
SMAN340 is disconnected from any pressure
source and at equilibrium with the ambient
pressure.
1 Press the CAL Atmospheric Pressure button and your SMAN340
will set the zero point of pressure to the ambient pressure.
Advanced Pressure Calibration
Your SMAN340 has the ability to perform a
linear adjustment of the pressure sensors based
on refrigerant type, temperature, and pressure.
Calibration setup:
For best results, first perform both the
Temperature and Pressure Zeroing procedures. See Calibration
section for details. This will ensure pressure readings are zeroed
and thermocouple is properly calibrated to the SLT port of the
SMAN. Calibration to LLT port is not necessary for this calibration.
The refrigerant cylinder should be stored in a stable ambient
environment for at least 24 hours before calibration.
1 Plug in a Type K thermocouple into SLT. (A bead type
thermocouple, like the ATB1, is recommended.)
2 Connect the SMAN340 to a refrigerant cylinder of a known,
single refrigerant using an EPA approved service hose. Be sure
to open both HIGH and LOW side valves on your manifold and
cap the unused ports. (If caps are not available you can connect
both ends of a refrigerant hose to the two unused caps. Note:
Some refrigerant will remain in the hoses which will need to be
recovered.)
3 Press the REFRIGERANT button to match the refrigerant of the
cylinder you are using.
4 Attach bead-type thermocouple to the side of the cylinder using
tape. It is recommended to attach in the middle of the cylinder.
Important: Let the temperature of the thermocouple stabilize to
the refrigerant temperature for 1 to 2 minutes or until stable.
5 Open the refrigerant cylinder. The pressure inside cylinder should
now be displayed on both HIGH and LOW side pressure sensors.
6 Press the CAL Test Pressure button. If successful, "Good" will
display for 3 seconds. If failed, "Err" will display for same time.
Your SMAN checks with its built-in P-T charts to compare the
temperature of the refrigerant in the tank to the vapor saturation
temperature based on the refrigerant you selected. If the measured
pressures on your SMAN are within ±3psi of the P-T chart pressure
corresponding to the vapor saturation temperature, the SMAN will
adjust the pressure sensor linearity to match the P-T chart.
Possible causes of failed "Err" pressure calibration:
1. Refrigerant tank was not stored in stable ambient conditions for at
least 24 hours.
2. Thermocouple attached to refrigerant tank was not properly
calibrated to SLT port of SMAN.
3. Thermocouple was plugged into wrong port LLT instead of SLT.
4. Incorrect refrigerant was selected on the SMAN.
Limited Warranty
This meter is warranted against defects
in material or workmanship for one year
from date of purchase from an authorized
Fieldpiece dealer. Fieldpiece will replace or
repair the defective unit, at its option, subject
to verification of the defect.
This warranty does not apply to defects
resulting from abuse, neglect, accident,
unauthorized repair, alteration, or unreasonable
use of the instrument.
Any implied warranties arising from the sale of
a Fieldpiece product, including but not limited
to implied warranties of merchantability and
fitness for a particular purpose, are limited to
the above. Fieldpiece shall not be liable for loss
of use of the instrument or other incidental or
consequential damages, expenses, or economic
loss, or for any claim of such damage, expenses,
or economic loss.
State laws vary. The above limitations or
exclusions may not apply to you.
Obtaining Service
Email Fieldpiece warranty department at
[email protected] for current fixed
price repair service. Send check or money
order made out to Fieldpiece Instruments for
the amount quoted. If your meter is under
warranty there will be no cost for the repair/
replacement. Send your meter, freight prepaid,
to Fieldpiece Instruments. Send proof of date
and location of purchase for in-warranty service.
The meter will be repaired or replaced, at the
option of Fieldpiece, and returned via least cost
transportation.
For international customers, warranty for
products purchased outside of the U.S. should
be handled through local distributors. Visit our
website to find your local distributor.
High Side
Low Side
TXV
Compressor
Direction of
Refrigerant
Flow
Condenser
Evaporator
!
WARNINGS
DO NOT APPLY MORE THAN 800 PSI TO ANY PORT ON THE MANIFOLD.
FOLLOW ALL EQUIPMENT MANUFACTURER'S TESTING PROCEDURES
ABOVE THOSE IN THIS MANUAL IN REGARDS TO PROPERLY
SERVICING THEIR EQUIPMENT.
Directly to
Service Port
Schrader Core
Removal Tool
Hose
To
Pump
MICRONS OF MERCURY
S
CUUM
U E
MIN
ALARM
ENTER
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176
TestEquipmentDepot.com
