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Lennox 78H55 65209700 Class 2 Transformer 120V to 24V 30VA

Name: Lennox 78H55 65209700 Class 2 Transformer 120V to 24V 30VA
Brand: Lennox
SKU: 66255112286
Price: 91.65 USD
Availability: InStock

Low stock: 1 left

$91.65 USD

Sale Sold out

Shipping calculated at checkout.

Lennox 78H55 Transformer Reliability & Troubleshooting

Restore Thermostat Power: Fixes the common issue of blank thermostat screens and unresponsive HVAC systems.
OEM Voltage Control: Prevents erratic furnace behavior caused by fluctuating low-voltage signals from generic transformers.
Safety Protection: Integrated Class 2 limiting prevents the transformer from becoming a fire hazard during a wiring short.
Quiet Operation: High-quality laminations prevent the "humming" or "buzzing" sound often heard in cheap aftermarket replacements.
Exact Footprint: Standard Lennox mounting tabs allow for a 5-minute swap without drilling new holes in the chassis.

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Specifications

Product Details:

Brand: Lennox
Manufacturer: Genuine OEM
Part Number: 65209700 (Cat # 78H55)
Weight: 1.5 lbs
Primary Voltage: 120 VAC / 60 Hz
Secondary Voltage: 24 VAC
Power Rating: 30 VA
Phase/Hertz: Single-Phase (1PH) / 60 Hz
Class: Class 2 Not Wet / Class 3 Wet

description

Introduction: Lennox OEM Focus and System Function

The Lennox 78H55 (Model 65209700) is the vital power-conversion "brain" for your furnace's control circuitry. As a genuine Class 2 transformer, its primary role is to step down 120VAC line voltage to a safe 24VAC output required for the thermostat, control board, and gas valve. It is a critical component for the Lennox Elite and Merit furnace series, ensuring that the low-voltage safety loop remains energized and stable. By using this specific OEM replacement, you guarantee the electrical isolation necessary to protect sensitive microprocessor-based control boards from high-voltage surges.

Key Features:

Genuine OEM Fit (78H55): Engineered by Lennox for an exact bolt-on replacement, eliminating the need for custom mounting brackets or wire splicing in the blower compartment.
Fixes "Dead System" Issues: Specifically designed to resolve no-power symptoms where the thermostat is blank and the furnace control board shows no LED diagnostic lights.
Class 2 Safety Rated: Includes internal thermal overload protection to prevent the transformer from overheating or causing a fire if a low-voltage short occurs.
Precision Voltage Regulation: Provides a stable 24V secondary output, which is essential for preventing relay "chatter" and noise in 24-volt contactors and solenoids.
OEM Reliability: Built with high-grade copper windings and a heavy-duty laminated core to ensure long-term durability in high-heat furnace environments.

Product Details:

Brand: Lennox
Manufacturer: Genuine OEM
Part Number: 65209700 (Cat # 78H55)
Weight: 1.5 lbs
Primary Voltage: 120 VAC / 60 Hz
Secondary Voltage: 24 VAC
Power Rating: 30 VA
Phase/Hertz: Single-Phase (1PH) / 60 Hz
Class: Class 2 Not Wet / Class 3 Wet

🛠️ HVAC Depot Pro Tip: The "Short Circuit" Check

Before installing the new 78H55 transformer, take a picture of the primary (black/white) and secondary (yellow/blue) wiring. If your previous transformer "burned out," there is likely a short in your thermostat wire or a bad contactor coil. Use a multimeter to check for 0 ohms between the 24V wires and ground. If you find a short, fix it before powering up the new transformer, or you will blow the new unit instantly.

Cross-Reference:

Superseded Numbers: 100057-01, 89K59, 100057-02
Legacy Numbers: 652097, 68H5501
Drawing Number: LB-53531A
White-Rodgers/Emerson Equivalents: 90-T40F3, 90-290Q

Model Compatibility:

G24 (Suffixes: -045, -060, -075, -100, -120)
G40 (Suffixes: -045, -070, -090, -110)
G50 (Suffixes: -045, -070, -090, -110)
G60 (Suffixes: -070, -090, -110)
G43 (Suffixes: -045, -070, -090, -110)
ML180 (Suffixes: E, XE, UH)
ML193 (Suffixes: UH)
EL180 (Suffixes: NE, XE)

Specification

Refund policy

Refund & Return Policy

Last Updated: June 2026

At HVAC Parts & Equipment Depot, customer satisfaction is important to us. This Refund & Return Policy explains how returns, exchanges, and refunds are handled for purchases made through TopHVACParts.com.

Return Eligibility

We accept returns within 30 days of delivery.

To qualify for a return:

The item must be unused, uninstalled, and in its original condition.
The item must be returned in its original packaging.
Model numbers and serial numbers must match the original purchase records.
Proof of purchase or order confirmation is required.

Non-Returnable Items

The following items are not eligible for return or refund:

Installed or used parts.
Products showing signs of installation, modification, or damage caused after delivery.
Items missing original packaging.
Sale or clearance items.
Special-order or custom-order products.
Returns requested more than 30 days after delivery.

Restocking Fee

Approved returns may be subject to a 20% restocking fee.

The restocking fee will be deducted from the refund amount after the returned item has been inspected and approved.

Damaged, Defective, or Incorrect Items

If you receive a damaged, defective, or incorrect item, please contact us within 7 days of delivery.

Email: support@tophvacparts.com
Phone: (214) 734-5222

We may request photographs and additional information to help process your claim.

If the claim is approved, we will provide a replacement, exchange, or refund at no additional cost to you.

Exchanges

We replace items only if they are defective, damaged upon arrival, or incorrectly shipped.

To request an exchange, contact us at:

support@tophvacparts.com

Refund Process

Once your return is received and inspected, we will notify you by email regarding approval or rejection of your refund request.

If approved:

Refunds will be issued to the original payment method.
Processing typically takes 7–14 business days after approval.
Your financial institution may require additional time before the refund appears in your account.

Return Shipping

Customers are responsible for return shipping costs unless the return is the result of:

Our shipping error,
A defective product,
A damaged product received upon delivery.

Original shipping charges are non-refundable.

We recommend using a trackable shipping service and purchasing shipping insurance for higher-value items.

Return Address

HVAC Parts & Equipment Depot
1135 E Plano Parkway, Suite 8
Plano, TX 75074
United States

Professional Installation Notice

Many HVAC products require installation by a licensed HVAC professional.

HVAC Parts & Equipment Depot is not responsible for damages resulting from improper installation, misuse, unauthorized modifications, or failure to follow manufacturer instructions.

Special Orders

Special-order products must be picked up within 30 days of purchase unless other arrangements have been approved.

Unclaimed special-order products may be returned to the manufacturer and may be subject to applicable restocking fees.

Contact Us

If you have questions regarding returns, refunds, or exchanges, please contact us:

HVAC Parts & Equipment Depot

Phone: (214) 734-5222
Email: support@tophvacparts.com

Refund & Return Policy

Last Updated: June 2026

Return Eligibility

We accept returns within 30 days of delivery.

To qualify for a return:

The item must be unused, uninstalled, and in its original condition.
The item must be returned in its original packaging.
Model numbers and serial numbers must match the original purchase records.
Proof of purchase or order confirmation is required.

Non-Returnable Items

The following items are not eligible for return or refund:

Installed or used parts.
Products showing signs of installation, modification, or damage caused after delivery.
Items missing original packaging.
Sale or clearance items.
Special-order or custom-order products.
Returns requested more than 30 days after delivery.

Restocking Fee

Approved returns may be subject to a 20% restocking fee.

The restocking fee will be deducted from the refund amount after the returned item has been inspected and approved.

Damaged, Defective, or Incorrect Items

If you receive a damaged, defective, or incorrect item, please contact us within 7 days of delivery.

Email: support@tophvacparts.com
Phone: (214) 734-5222

We may request photographs and additional information to help process your claim.

If the claim is approved, we will provide a replacement, exchange, or refund at no additional cost to you.

Exchanges

We replace items only if they are defective, damaged upon arrival, or incorrectly shipped.

To request an exchange, contact us at:

support@tophvacparts.com

Refund Process

Once your return is received and inspected, we will notify you by email regarding approval or rejection of your refund request.

If approved:

Refunds will be issued to the original payment method.
Processing typically takes 7–14 business days after approval.
Your financial institution may require additional time before the refund appears in your account.

Return Shipping

Customers are responsible for return shipping costs unless the return is the result of:

Our shipping error,
A defective product,
A damaged product received upon delivery.

Original shipping charges are non-refundable.

We recommend using a trackable shipping service and purchasing shipping insurance for higher-value items.

Return Address

HVAC Parts & Equipment Depot
1135 E Plano Parkway, Suite 8
Plano, TX 75074
United States

Professional Installation Notice

Many HVAC products require installation by a licensed HVAC professional.

HVAC Parts & Equipment Depot is not responsible for damages resulting from improper installation, misuse, unauthorized modifications, or failure to follow manufacturer instructions.

Special Orders

Special-order products must be picked up within 30 days of purchase unless other arrangements have been approved.

Unclaimed special-order products may be returned to the manufacturer and may be subject to applicable restocking fees.

Contact Us

If you have questions regarding returns, refunds, or exchanges, please contact us:

HVAC Parts & Equipment Depot

Phone: (214) 734-5222
Email: support@tophvacparts.com

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William Bartlett

Cecil really saved me with troubleshooting tips over the phone. Thought I was going to have to replace the blower motor and ended up only needing a motor run capcitor. Thank you and God bless!

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Cecil and Fidel were absolutely amazing and so helpful. We were happy they were open on Sunday, but was impressed with their knowledge and willingness to make sure we had everything we needed. If you need parts or service or install, I would recommend.

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Our AC went out during the hottest stretch of summer, and with a one-year-old at home, we were desperate for a quick fix. These guys came through big time — not only did they source the part faster than anyone else in the area, they also walked me through DIY troubleshooting while I waited. Trustworthy, knowledgeable, and run by a solid local family. As someone who owns rental properties nearby, I’ll be sourcing all my HVAC parts from them moving forward. Highly recommend!

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Had a power outage last night and during the 100 degree heat today noticed that the AC was not blowing any cold air. Pulled the capacitors to have them checked and also took video of the relay making noise even with the breaker was off. The proprietor and her staff were very friendly and helpful. She had the video analyzed and confirmed something was wrong. She checked one of the capacitors was a little low. Capacitor replacement is the biggest ticket item for HVAC repair. It is hundreds of dollars with the a capacitor only about $20.

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Cecil and his family have been a life saver. I walked in with very little knowledge on parts let alone how to repair my unit. All I had was my brother in FL who knows more than I do and Cecil at HVAC Depot. With 2 young kids at home I couldn't afford to wait for a HVAC tech. Cecil walked me through what I needed to know, even after hours when the shop closed. I successfully repaired the fan motor and replaced the capacitor. Thank you HVAC team for being totally awesome. Prices were amazing and I'm forever going to support this small family business. You and your family are what Texas is all about!!!

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My AC went out in our home on Friday night. I went out and got the capacitor details and took them here first thing Saturday morning. Lady at the counter was friendly and had the capacitor I needed! When I got home, I installed the capacitor and AC is all good!!

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Thanks for everything

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Frequently Asked Questions

Questions? We’ve got you covered

Can anyone buy from your store, or do I need to be a licensed contractor?

We are open to the public! Homeowners, landlords, and DIYers are all welcome—no license required.

What kinds of HVAC parts do you sell?

We carry blower motors, fan motors, capacitors, control boards, contactors, thermostats, filters, copper lines, refrigerants, and more.

Do you sell parts for specific brands like Trane, Goodman, or Lennox?

Yes, we stock OEM and compatible replacement parts for major brands including Trane, Goodman, Lennox, Carrier, Rheem, and others.

Can you help me find the right part for my system?

Absolutely! Bring in the part, model number, or a picture, and our team will help match you with the correct replacement.

Do you offer returns or exchanges on parts?

Yes, we accept returns or exchanges within a set time period—just make sure the item is unused and in original packaging. Ask for specific terms at the counter.

Do you provide technical support or installation services?

While we don't install, we can answer basic questions and refer you to trusted local HVAC technicians if needed.

Do you sell refrigerants to the public?

We sell certain refrigerants, but EPA regulations require certification for purchase of products like R-410A or R-22.

Do you ship parts, or is it in-store only?

We offer both! You can shop in person or call to arrange shipping if you're out of town.

Lennox 78H55 65209700 Class 2 Transformer 120V to 24V 30VA