What MFD capacitor do I need for my Lennox AC?

The correct replacement for Lennox model OEM Lennox Dual Run Capacitor — 21W81 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 Dual Run Capacitor — 21W81.

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.

Lennox

OEM Lennox Dual Run Capacitor — 21W81

Name: OEM Lennox Dual Run Capacitor — 21W81
Brand: Lennox
SKU: LNX-21W81
Price: 18.95 USD
Availability: InStock

SKU: LNX-21W81 Brand: Lennox

$18.95 $24.95

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The genuine OEM Lennox 21W81 dual run capacitor delivers the starting and running torque required by both the compressor and condenser fan motor in your Lennox outdoor unit. By storing and releasing electrical energy on demand, this single dual-rated component keeps both motors turning efficiently and is essential to reliable cooling and heat pump operation.

Capacitors fail more often than almost any other HVAC electrical part. Warning signs of a failing 21W81 include a fan or compressor that hums but does not spin, weak or inconsistent cooling, breakers that trip, or a bulging, leaking, or burnt capacitor housing. A degraded capacitor makes motors draw higher amperage, and ignoring it can accelerate wear on the far more expensive compressor.

OEM matters with Lennox equipment. The 21W81 is built to the precise microfarad (MFD) and voltage specifications engineered for your system, guaranteeing correct motor startup, safe electrical performance, and rated efficiency. Off-brand capacitors with approximate ratings can cause overheating, nuisance failures, and reduced equipment life. Install the factory-specified part for a dependable, lasting repair.

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 Dual Run Capacitor — ...

$18.95

Frequently Asked Questions

Does this Capacitor fit my Lennox OEM Lennox Dual Run Capacitor — 21W81?

Yes. This is the factory-specified OEM capacitor for the Lennox OEM Lennox Dual Run Capacitor — 21W81. 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 Dual Run Capacitor — 21W81?

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 Dual Run Capacitor — 21W81

Shipping Information

Return Policy

Frequently Asked Questions