One of our customers has an older Lennox air conditioner. The air conditioner was installed when the home was built in around 1980. We are out every year to maintain this unit for the homeowner. And it is still running today (as of the spring of 2019). The unit is a Lennox model HS9-461-4P R-22 unit. This AC unit was built so early in production that the serial number for the unit is 51. That is correct, 51. To put this serial number in perspective, a recent Lennox heat pump that we were working on had serial number 1914D48175. This blog has some information about these very well built older Lennox air conditioners. Maybe you still have one of these old AC units and you are struggling to find technical information on them. This unit has an older mercury thermostat as well.

Accurate Heating & Cooling Is A Trane Comfort SpecialistAccurate Heating & Cooling Banner ImageAccurate Heating & Cooling has BBB A+ Rating

Your Trusted Omaha HVAC Provider

Accurate Heating & Cooling services all makes and models of air conditioners. We routinely install Trane and Armstrong brand equipment. While we can and sometimes do install any brand, we find that our customers are happy with the reliability of these two established brands. Call us today at 402-238-2425 to have your air conditioner serviced or repaired. We will also service your furnace and other HVAC equipment.

The Venerable Lennox HS9 Air Conditioner described above is pictured below

Lennox Model HS9 Air Conditioner Outdoor Unit

In case you fail to fully believe the serial number as being 51, the picture below shows the manufacturers label plate from the unit. The tonnage rating of the air conditioner is usually found embedded in the unit model number. Not so with this older unit.

Lennox Model HS9 Air Conditioner Outdoor Unit Manufacturer's Label Plate


A close up of the serial number shows it as 51. Only two digits. Unbelievable.

Lennox Model HS9 Air Conditioner serial number


Lennox HS9 Air Conditioner Condenser

Viewed from a different angle below, the condenser coil is visible as is the condenser fan on top.

Lennox Model HS9 Air Conditioner condenser


The components have stencil markings on them which must have been the method of labeling components back then. The components used in this early model air conditioner are still the basic components used in some base model air conditioners today.

Lennox Model HS9 Air Conditioner compressor compartment with contactor


Lennox Model HS9 Air Conditioner Wiring Diagram

The wiring diagram for the air conditioner is shown below.

Lennox Model HS9 Air Conditioner wiring diagram

And an operation, maintenance, and installation manual was located for the Lennox HS9 series air conditioner. Check out the pdf version of the Lennox HS9 series air conditioner Serial 51 here.

It is pretty unusual for a unit this old to still be reliably cooling a home. Regular maintenance was certainly a factor in the longevity of this unit. For some information on homeowner maintenance items that will help extend the life of your HVAC system, refer to this blog. And if you need servicing for your residential air conditioner, just give us a call.

The photo below is of JJ making repairs to a heat pump for one of our residential customers.

HVAC Technician Repairing Outdoor Unit

Additional Information

Accurate Heating & Cooling is an established HVAC contractor. We have been in business since 1998. Check out what our customers are saying about us at our Customer Testimonials page. And check out our A+ rating with the BBB.

Accurate Heating & Cooling Is A Trane Comfort SpecialistAccurate Heating & Cooling Banner ImageAccurate Heating & Cooling has BBB A+ Rating