Mueller Model D Fre-Heater Installation and Operation Manual
Effective March 1, 1993
Part No. 8800430
Revised November 6, 2019
2.11
SPECIAL MODEL “DE” FRE-HEATER OPERATING INSTRUCTIONS
The electrical heating element in Model “DE” Fre-Heaters allows a reserve of hot water to be stored in the top of the
tank when the condensing unit usage is low or when high water output is desired. The thermostat for the electric
heating element has been set at the factory for 140°F to reduce the risk of a scald injury. Should it be necessary
to change this setting, turn off the power to both the water heater and the condensing unit, remove the access
plate, and adjust the temperature pointer to the desired temperature (shown approximately on the dial) with a
screwdriver. Be careful not to disturb the plastic shield covering the electrical connections. The use of higher
settings for the thermostat reduces the amount of savings that the refrigerant heat recovery provides.
DANGER: Hydrogen gas can be produced in a hot water system served by this heater that has not been
used for a long period or time (generally two weeks or more). Hydrogen gas is extremely flammable. To
reduce the risk of injury under these conditions, it is recommended that a hot water faucet be opened for
several minutes before using any electrical appliance connected to the hot water system. If hydrogen is
present, there will probably be an unusual sound such as air escaping through the pipe when the water
begins to flow. There should be no smoking or open flame near the faucet at the time it is open.
The electrical heating element circuit contains controls that disconnect the electrical power to the element should
the tank water temperature rise above 190°F. This is a non-resetting control, so it will need to be reset each time the
tank temperature reaches 190°F.
2.12 MAINTENANCE
In order to achieve the maximum life from Model “D” Fre-Heaters, the following should be done annually:
1. Remove and check at least one of the two anode rods. If the anode is 33% or more consumed, both anode rods
should be replaced.
2. Drain and backflush the water tank running enough water from the water inlet or drain to remove all loose
scale that has collected in the bottom of the water tank.
3. Check the operation of the pressure temperature relief valve by manually operating it to see that it will freely
flow water should it be required to do so. If there is any doubt that it will not function properly, replace it.
4. Check all water fittings, valves, etc. to be sure there are no water leaks. Repair as necessary.
5. Check the operation of all controls, such as the hot gas bypass valve, Aquastat, electric element controls,
refrigeration head pressure controls, or any other controls necessary, for the proper operation of the Mueller
Fre-Heater and the refrigeration and/or air conditioning systems it is connected to.
NOTICE: All illustrations and diagrams in these instructions are schematic suggestions only and do not
attempt to address all of the important design considerations, such as pipe sizing and configuration or the
selection and placement of major system components. Every installation must follow known and accepted
industry safety practices and various code or legal requirements.
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