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TM077: 325 & 410 Series II Heat Pump Service Instructions
Rev 00: Issued April 2014
Suction and Discharge Pressure Vs Run Time (20 degree ambient, from cold tank)
Electrical Insulation Testing
There are three basic test procedures that should be carried out when the operation and
function of a heat pump water heater‟s electrical system is in doubt.
Insulation Resistance of the Neutral Circuit: Reading should be above 1 megaohm.
1. Isolate power to the water heater at the isolation switch. Confirm that
voltage is not present, with a multi-meter across the active and neutral
terminals at the terminal block.
2. Once satisfied that the water heater is electrically isolated, disconnect the active and
neutral wires from the water heater terminal block.
3. Connect megger leads to the neutral of the water heater wiring and earth.
4. Operate megger on the 500V DC setting. A reading above 1 MΩ should be obtained.
5. If a reading below 1 MΩ is indicated, all component parts will need to be individually
tested to locate the fault. Refer to flow diagram below.
Insulation Resistance of the Active Circuit: Reading should be above 1 megaohm.
6. Connect megger leads to the active of the water heater wiring and earth.
7. Operate megger on the 500V DC setting. A reading above 1 MΩ should be obtained.
8. If a reading below 1 MΩ is indicated, all component parts will need to be individually
tested to locate the fault. Refer to flow diagram below.
Earth Continuity: Reading should be below 0.5 ohms.
9. With multimeter leads across the storage tank earth connection and the storage tank
jacket, confirm the resistance is less than 0.5Ω.
10. With multimeter leads across the storage tank earth connection and the heat pump
module jacket, confirm the resistance is less than 0.5Ω.
11. If a reading above 0.5Ω is indicated, use the wiring diagram (page 26) to determine the
location of the faulty earth connection.
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