Fieldpiece AVG2 User Manual
Vacuum Gauge
Accessory Head
Model: AVG2
Description
The AVG2 vacuum gauge accessory head is a
thermistor based digital multimeter accessory that
enables most digital multimeters to digitally measure very low pressures associated with evacuating
moisture from air conditioning and refrigeration systems. It measures pressures between 50 and 2000
microns of mercury.
By selecting the proper range on the DMM, you
can verify that everything is properly connected and
the pressure is going down from atmospheric pressure to 2000 microns.
The sensor has been designed to withstand pressures up to 500 psi (3400kPa) so that no damage to
the AVG2 will occur if it is exposed to full system
pressures.
Applications
Measure the vacuum on a refrigeration system
when evacuating refrigerant. The digital readout
shows even small drops in pressure. While target
vacuum pressures vary, the technician typically
wants a vacuum between 300 and 400 microns for
small systems and 700 for large systems.
How it works
Power is delivered to a thermistor which is
exposed to the vacuum being tested. Molecules
from the gas conduct heat from the thermistor. The
fewer gas molecules there are, the less heat is
taken away. The power to the resistor is adjusted to
keep the temperature of the thermistor within a narrow range. The lower the power required by the
resistor, the lower the pressure. The power delivered to the thermistor is measured and scaled to
pressure. It is very important that the thermistor
sensor be kept clean and free of oil to enable unimpeded flow of heat from the thermistor.
LED Indicators
INC: When the pressure is increasing, the LED will
blink at a rate relative to the rate of pressure
increase.
DEC: When the pressure is decreasing, the LED
will blink at a rate relative to the rate of pressure
decrease.
STABLE: When the rate of change of pressure is
zero, the LED will light.
ON: When the AVG2 is on, the LED will light.
LO BAT: When the batteries need replacement,
the LED will light.
How to use
1. Connect AVG2 vacuum gauge head to
VOLTS/OHMS and COM jacks on meter and
select mVDC. Slide onto “Stick” meter, EHDL1
Electronic Handle or DL3 Data Logger. You can
also connect to meters with a mVDC scale and
industry standard jacks by using ADLS2 test
leads or AHDL1 Adapter Handle.
2. Hand tighten your service hose from the refrigeration/AC system service port to the AVG2.
3. Your meter will readout pressure in microns of
mercury. Disable auto-off for long evacuations
or for data logging with the DL3.
4. To view the pressure dropping from atmospheric
pressure to 2000 microns, set DMM to VDC
range. Once reading is below 2.0, change range
to mVDC to display pressure in microns.
Converts
1 micron of
mercury to
1mVDC
Vacuum
Gauge
Accessory
Head
AVG2
INC
DEC
ON
LO BATT
STABLE
Specifications:
Sensor: Precision thermistor
Fitting: Standard 1/4” flared brass fitting (male)
Conversion rate: 1 mVDC/1 micron of mercury
Range: 50 to 2000 microns of mercury
Resolution: 1 micron of mercury
Accuracy: +/-10% or +/-10 microns, (50 to 1000
microns) @ 73°F ±9°F (23°C ±5°C), <90%RH.
Operating environment: 32 to 122°F (0 to 50°C)
@ <75%RH
Storage environment: -4 to 140°F (-20 to 60°C)
@ <80%RH with battery removed
Pump down indication: When pumping down
from atmospheric pressure to 2000 microns,
output of head goes from over 3VDC to 2VDC.
Overload: 500psi (3400kPa)
Battery: 9V
Battery life: 35 to 40 hours typical (alkaline). Red
LED indicates battery is below operating level.
Auto-off: To extend battery life, the AVG2 auto-
matically turns off after 5 minutes when reading
above 70,000 microns. The auto-off switch is
located beneath the rubber covering. Use it to
disable auto-off function.
Precautions and troubleshooting
Before working on the system, make sure there
are no leaks. A leak can make it impossible to pull
the desired vacuum.
If there are no leaks, the vacuum gauge is properly connected and working, and the pump is working properly, it may just be a matter of time before
the vacuum reaches the desired level. Moisture or
gas pockets can cause the vacuum level to remain
high until they are completely drawn out. With the
DMM in the VDC position, you can see even small
changes in pressure as the system pumps down.
If the vacuum gauge doesn’t seem to work properly and you are sure you don’t have leaks, check
for contamination of the sensor.
To check the vacuum gauge and the pump, connect it directly to a refrigerant pump using a very
short hose. If the pump is in good shape, you
should be able draw a vacuum down to 200 microns
in a couple of minutes. If you are unable to draw the
vacuum down to these levels, check for leaks
and/or thoroughly clean the well of the sensor with
isopropyl (rubbing) alcohol.
Cleaning the sensor
Drip isopropyl (rubbing) alcohol into the opening
of the sensor and pour it out, flushing any contaminants along with it. Leave the sensor opening
uncovered long enough to completely evaporate
any leftover alcohol. Do not use an object such as a
cotton swab to clean the sensor; you may cause
damage to the sensor.
Warranty
The product is warranted to the original purchaser against defects in material or workmanship for a
period of one (1) year from the date of purchase.
During the warranty period, Fieldpiece Instruments
will, at its option, replace or repair the defective unit.
This warranty does not apply to defects resulting
from abuse, neglect, accident, unauthorized repair,
alteration, or unreasonable use of the instrument.
Any implied warranty arising out of the sale of
Fieldpiece's products including but not limited to
implied warranties of merchantability, and fitness for
purpose, are limited to the above. Fieldpiece shall
not be liable for incidental or consequential damages.
Service
Return any defective AVG2 to Fieldpiece for warranty service along with proof of purchase. Contact
Fieldpiece for out of warranty repair charges.
WARNING
When connecting hoses to the AVG2 vacuum gauge head, HAND TIGHTEN ONLY! DO
NOT USE WRENCHES OF ANY KIND. Use
only hoses with knurled fittings.
!
!
v09
OPERATOR’S MANUAL
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