Thermo Pride OMD-70 - Manual (Page 41)

All installations and services must be performed by qualified service personnel.
B. CAD CELL CHECKOUT PROCEDURE: (OMD ONLY)
1. Remove cad cell lead wires, then start the burner. Shortly after burner starts, place a
temporary jumper between terminals f & f of the oil primary control. Connect ohmmeter
across cad cell lead wires - resistance should be less than 1600 ohms.
2. Stop the burner and remove temporary jumper.
3. With the burner off, check dark cell resistance across cad cell lead wires. Resistance
should be greater than 20,000 ohms. If cell resistances are different from above, recheck
wiring, location of cell, etc. If necessary, replace plug in portion of cell, (Part No.
350104).
4. Reconnect cad cell lead wires. Check out the oil primary control according to the
instructions packed with the control.
C. HEAT EXCHANGER CLEANING INSTRUCTIONS
: The heat exchanger must be cleaned by a qualified service person.
For oil-fired units, it is important to inspect and clean the heat exchanger once a year, or as
necessary, to remove any build-up of soot. A layer of soot on the inside of the heat exchanger
will act as an insulator, reducing heat transfer, resulting in reduced efficiency
For gas-fired units, the presence of a layer of soot on the heat exchanger is a strong indicator
of incomplete combustion. The burner adjustment should be rechecked as well as the firing
rate, the combustion air supply, and the vent system.
To clean the heat exchanger,
1. First, turn off all power to the unit.
2. Remove the clean-out plate, immediately above the burner (refer to Figure 8), to gain
entry to the cleanout covers.
3. Remove cleanout covers, the vent connector pipe to the chimney, the burner and the
burner mounting plate. When removing the cleanout cover, special care must be taken
not to damage the gaskets or high limit switch.
NOTE: The high limit switch may be removed for easier access to the left-hand cleanout
cover by removing the two (2) limit mounting screws. The limit must be reinstalled in the
original orientation before operating the furnace.
Should the gaskets separate, crack, break, or otherwise not be able to provide the
necessary seal, the gasket must be replaced before reattaching the cleanout cover.
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