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Lennox

OEM Lennox Potential Relay — 51M04

SKU: LNX-51M04 Brand: Lennox
$24.95 $34.95

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Texas CMBL #19328542014
SAM.gov Registered
Govt POs Accepted

The genuine OEM Lennox 51M04 potential relay controls the start capacitor in your compressor or motor circuit. During startup it keeps the start capacitor in the circuit to provide extra torque, then drops it out once the motor reaches speed based on the back-EMF (potential) it senses — protecting the start capacitor from overheating.

Common failure symptoms: A failed 51M04 often results in a compressor that hums but won't start, trips the breaker, or starts hard and struggles. Because the relay and start capacitor work together, a bad relay can burn out capacitors repeatedly or leave the start cap in the circuit too long, leading to nuisance overload trips and premature compressor wear.

Why OEM matters: Potential relays must match the correct pick-up and drop-out voltages for the motor they serve. The OEM Lennox 51M04 is spec'd to the exact voltage thresholds and contact rating your Lennox equipment requires, ensuring reliable starts and protecting the compressor and start capacitor from damage that mismatched generic relays commonly cause.

Shipping Information

  • Orders placed before 3PM CST ship same business day
  • Standard delivery: 2-5 business days
  • Express shipping available at checkout
  • Free shipping on orders over $75
  • Tracking number emailed upon shipment

Return Policy

  • 30-day returns on unused parts in original packaging
  • Electrical parts (capacitors, contactors, control boards) are final sale once installed
  • Email info@nationalhvacparts.com to initiate a return
  • Refunds processed within 5-7 business days

Frequently Asked Questions

Does this Relay fit my Lennox OEM Lennox Potential Relay — 51M04?
Yes. This is the factory-specified OEM relay for the Lennox OEM Lennox Potential Relay — 51M04. It is a direct drop-in replacement that fits without modification. Always verify the model number on your equipment nameplate before ordering.
How do I replace the relay on my Lennox OEM Lennox Potential Relay — 51M04?
Refer to your equipment service manual for model-specific steps. General approach: turn off power, photograph connections, remove old part, install new part, restore power and test. For gas components, hire a licensed technician. Email info@nationalhvacparts.com for guidance.
What symptoms mean I need a new relay?
Common symptoms: unusual noises, intermittent operation, complete failure, or visible damage. Visit our diagnostic hub for symptom-based troubleshooting.
Is this relay compatible with Bryant or Payne too?
Many Lennox parts are cross-compatible with Bryant and Payne since all three brands are manufactured by Carrier Global Corporation. The same physical part is often used across brand labels with different model numbers. To verify: check your Bryant or Payne equipment service manual for cross-compatible part numbers, or email info@nationalhvacparts.com with your model number.
Should I use OEM or aftermarket for my Lennox relay?
OEM recommended for reliability and warranty compatibility. OEM parts match exact factory specifications for proper fit, performance, and safety. While aftermarket alternatives cost less upfront, the risk of improper fit and reduced lifespan usually makes OEM the better value long-term.
How fast does National HVAC Parts ship?
Orders placed before 3:00 PM CST ship the same business day. Standard delivery is 2–5 business days anywhere in the continental United States. Express shipping available at checkout. We ship from Houston, TX to all 50 states. 30-day return policy on all parts.
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Mike Rivera
HVAC Parts Specialist — Online