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Control boards rely on low-voltage signals to run operations smoothly. When an old board stops responding or fails to regulate temperature properly, finding an exact match by part number ensures the system continues to work as intended.
Specifications
- Part number: 300678
- Brand: Cleveland
- Part type: Temperature control board
- Height: 3.05 in / 7.75 cm
- Length: 3.4 in / 8.64 cm
- Width: 4.55 in / 11.56 cm
- Part number: listed as a replacement for yours
- Ignition type: same as your furnace
- Wiring: photo every wire first
From the maker's and parts sellers' listings for this number. Compare them with the label on your old part.
What the Temperature Control Board Does
A temperature control board serves as the brain for managing temperature calls. It processes sensor inputs and directs power to components to start or stop heating cycles.
Most control boards use a 24 V control signal supplied by a step-down transformer. When the board fails, the equipment may fail to reach the desired temperature, cycle erratically, or stop running entirely.
Understanding the Board Specifications
Physical dimensions are critical for ensuring the replacement board mounts securely into the existing control compartment without straining wires.
The Cleveland 300678 control board features the following dimensions from the manufacturer specifications:
- Height: 3.05 in / 7.75 cm
- Length: 3.4 in / 8.64 cm
- Width: 4.55 in / 11.56 cm
How to Confirm a Match
Control boards can look similar across different models, but internal circuits differ. Always match by part number rather than physical appearance alone.
Inspect the label on your existing board. Look for the part number 300678 directly printed on the board surface or stamped on the manufacturer sticker. Check that the mounting holes and board footprint match the original component.
Safe Removal and Installation Steps
Control boards connect to many individual wires. Careful documentation before disconnecting anything prevents wiring mistakes during installation.
- Turn off the electrical power at the breaker panel and test the connections with a meter to verify no voltage remains.
- Take clear photos of every wire and terminal connection on the old board before loosening any fasteners.
- Label individual wires if the markings are faded or difficult to read.
- Remove the mounting hardware holding the old board in place.
- Mount the replacement board into the original location using the existing mounting points.
- Move wires one at a time to the matching terminals on the new board, referring to your reference photos.
- Restore power at the breaker and test system operation.
Read your old part
- Locate the identification sticker or stamp on your existing control board.
- Read the part number directly off the old part and check that it reads 300678.
- Check that the board dimensions match 3.05 in / 7.75 cm height, 3.4 in / 8.64 cm length, and 4.55 in / 11.56 cm width.
- Verify that the terminal layout and wiring connections align with your existing system setup.
When to call a pro
Board swaps can involve complex wiring, setup, and safety testing. If you are not confident testing for electrical power or mapping connections, stop and call a licensed technician.
Questions
What control voltage does this type of board typically use?
Most control boards use a 24 V control signal supplied by a transformer. Always test for power before touching any wiring connections.
What should I do before unplugging wires from my old board?
Take clear photos of every wire and connection point before removing anything. Label each wire clearly so you can transfer them one at a time to the same spots.
Can I bypass a safety switch to test if my control board is bad?
No. Never bypass limit switches, rollout switches, pressure switches, or any other safety devices. These controls protect your equipment and property from damage.
What are the physical dimensions of the Cleveland 300678 board?
This board measures 3.05 in / 7.75 cm in height, 3.4 in / 8.64 cm in length, and 4.55 in / 11.56 cm in width.
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Brand names and part numbers identify the part and show fit. HVAC Fitter is not affiliated with, authorized by, or endorsed by any equipment maker. If you are not sure a repair is safe for you, call a licensed HVAC technician.