Install Instructions

M500 Insulation Tester Guide – Megohm Meter
Features
• Full range scale up to 1000 Megohms
• Zone scale to indicate condition of insulation
• Operates on (2) “C” batteries (not included)
• Test leads store inside meter
How to test a Hermetic Compressor or motor
• Do Not test a compressor under vacuum.
• When testing a fan or condenser motor, run the
motor so it heats up and evaporates any
moisture on the windings. Moisture can cause
the M500 to give false low readings.
1. Remove the back cover and connect (2) new “C”
size batteries as indicated inside the meter. Replace
batteries as needed. If M500 battery supply drops
below 2.8 volts, it can give inaccurate readings
2. Remove all connecting wires from the compressor
or motor.
3. Attach Red test lead from the M500 to the
compressor as shown in Figure 1. Make sure the
black lead is attached to an unpainted part of the
compressor or motor chassis.
4. Press the “Red” button on the M500. Do Not touch
the M500 leads when the button is pressed. The
green “ON” light should illuminate immediately. (If
the light doesn’t turn on, disconnect the M500,
check the batteries. Replace batteries if needed.)
5. After the “ON” LED is lit, wait 10 seconds then
check the Megohm LED value. On small
compressors or motors the M500 Megohm LED’s
may turn on then quickly turn off. This indicates the
value is above 1000 meg-ohms. (See F1)
6. If M500 reading is “GOOD”, release the Red button
and move the red wire to each remaining leg for
testing and repeat step 5.
7. If only the 20 megohm LED is lit, this indicates that
the insulation value is low or shorted to ground.
(Check the compressor/motor with an ohm meter.
If the ohm meter reads a short, replace the
compressor/motor.) If the ohm meter reads open,
this indicates compressor/motor insulation
breakdown. (See F2)
Applications
• Hermetic compressors
• Condenser and blower motors
• Circuit Boards and transformers
• Ground loop and conduit wiring
• Panel boards and relay control
circuits
Specifications
• Indicator range: 20 to 1,000
Megohms
• Applied voltage: 500 volts
• Display: LED’s Dimensions:
3-3/8” x 6-3/8” x 1-3/4”
• Power source: (2) “C”
batteries
• Test leads: 24” long
w/alligator clip and magnet
(old design used 8” leads
with standard clips)
F1. Release button and make
sure leads are connected and
making contact. Test again to
make sure windings are good.
F2. A megohm reading of 20 to
100 may indicate a lack of
maintenance. Check for
contaminated oil or dirty motor
windings.
Warning Hazardous Voltage
Contact may cause electrical
shock and injury. Disconnect
all power before servicing.
Sealed Unit Parts Co., Inc
P.O. Box 21, 2230 Landmark Place
Allenwood, NJ 08720, USA
Figure 1