What MFD capacitor do I need for my Lennox AC?

The correct replacement for Lennox model OEM Lennox Start Capacitor — 21J29 is this exact part. It is the factory-specified replacement with exact OEM specifications. Using a part with different specifications can cause equipment damage or void your warranty. You can verify this by checking the data plate on your Lennox equipment which lists the model number OEM Lennox Start Capacitor — 21J29.

My AC hums but will not start. What part do I need?

An AC that hums but will not start is the classic symptom of a failed capacitor. The capacitor provides the electrical boost needed to start the compressor and fan motors. When it fails, you hear the hum of the motor trying to start but it cannot overcome inertia. Other symptoms include the fan spinning slowly, the AC cycling on and off rapidly, or a visibly swollen or leaking capacitor. Replacement cost: $15 to $80 for the part, DIY in 30 minutes.

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Lennox

OEM Lennox Start Capacitor — 21J29

Name: OEM Lennox Start Capacitor — 21J29
Brand: Lennox
SKU: LNX-21J29
Price: 18.95 USD
Availability: InStock

SKU: LNX-21J29 Brand: Lennox

$18.95 $24.95

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The genuine OEM Lennox 21J29 start capacitor delivers the high-torque burst of energy needed to get your compressor or motor spinning at startup. Wired into the motor's start winding, it provides the phase shift required to overcome initial inertia, then drops out of the circuit once the motor reaches running speed. This part is engineered to the exact microfarad and voltage ratings specified for your Lennox equipment, ensuring reliable startups season after season.

Common failure symptoms: When the 21J29 weakens or fails, you'll often hear a humming or clicking sound as the motor struggles to start, notice the unit tripping the breaker, or find the compressor won't turn on at all. A bulged, leaking, or swollen capacitor case is a clear sign it needs replacement. Hard starts and short-cycling also point to a failing start capacitor.

Why OEM matters: Lennox systems are calibrated to precise electrical specifications. Installing the factory 21J29 guarantees the correct capacitance and voltage tolerance, protecting your compressor from damaging power draw and preventing premature motor wear. Generic substitutes risk mismatched ratings that shorten equipment life and void coverage. Choose the OEM part for a direct fit and rated performance.

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

OEM Lennox Start Capacitor — 21J29

$18.95

Frequently Asked Questions

Does this Capacitor fit my Lennox OEM Lennox Start Capacitor — 21J29?

Yes. This is the factory-specified OEM capacitor for the Lennox OEM Lennox Start Capacitor — 21J29. 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 capacitor on my Lennox OEM Lennox Start Capacitor — 21J29?

Difficulty: Easy (20–30 min)
Step 1: Turn off power at breaker. Step 2: Open condensing unit panel. Step 3: Photograph the old capacitor wiring (Common/Herm/Fan). Step 4: Discharge old capacitor with insulated screwdriver. Step 5: Disconnect and remove old capacitor. Step 6: Mount new capacitor, reconnect wires to matching terminals. Step 7: Close panel, restore power, test. Tools: screwdriver, needle-nose pliers.

My AC hums but won’t start. What part do I need?

An AC that hums but won’t start is the classic symptom of a failed capacitor. The capacitor provides the electrical boost to start the compressor. When it fails, you hear humming but the motor can’t overcome inertia. Other symptoms: fan spinning slowly, AC cycling on/off rapidly, or a visibly swollen capacitor. Fix: replace capacitor ($15–$80 DIY, 30 min).

Is this capacitor 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 capacitor?

OEM strongly recommended. OEM capacitors have ±6% MFD tolerance vs aftermarket ±10%. The looser tolerance causes motor winding stress, higher temps, and shorter compressor life. Price difference is only $10–$20 — OEM is the clear value choice.

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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OEM Lennox Start Capacitor — 21J29

Shipping Information

Return Policy

Frequently Asked Questions