This article was written by Regan Murphy. Thanks, Regan!

Disclaimer: Any percentages used are the opinion of the author and not based on any actual facts.

You are probably already used to getting the model and serial numbers of the equipment. You may have even made a habit of getting the part number, but there are two commonly overlooked numbers on the part that you should always look for.

When you have a failed part, you should gather the following information:

• Equipment model number (or product number)
• Equipment serial number
• Equipment manufacturer part number (Carrier, Ruud, Trane, etc.) – I will refer to this as EMPN
• Part manufacturer model number (White-Rodgers, GE, Honeywell, Lau, Norton, etc.) – I will refer to this as PMMN

Equipment model number (or product number)

This is typically the first thing needed when looking up replacement parts. Carrier/Bryant/ICP units typically will have a “product number” used for looking up parts. The product number is the same as the model number, except it has extra digits at the end. For Carrier/Bryant/ICP units, you’ll want to get the product number instead of the model number (or get both).

Equipment serial number

This is used to look up or determine warranty information on a unit. Some manufacturers also allow you to search by serial number to pull up the model number, which comes in handy if you write down the model number incorrectly or take an unclear picture of the nameplate.

Equipment manufacturer part number (EMPN)

This is the part number the manufacturer assigns to a part made by someone else that they install on their equipment. We use this part number to look up a replacement part from a specific manufacturer.

Part manufacturer model number (PMMN)

This is the model or part number from the part manufacturer, where the parts initially come from. Part manufacturers sell their parts to HVAC equipment manufacturers, who then install the parts in their units.

You may not always be able to identify both an EMPN and PMMN on an existing part, but you’ve got a much better shot at finding the right replacement part if you can get one or the other.

If you make it a habit to look at the PMMN when you service units, you will better understand who makes what components. If you use universal replacement parts, the PMMN will be listed more frequently than the EMPN. That’s a big enough reason alone to pay attention.

If you know the PMMN, you’ll have more options for proper replacement parts from more suppliers than if you only know the EMPN.

Cross-referencing parts is worthy of an article or two on its own, so we will just look at the PMMN for three common gas furnace parts.

Gas furnaces:

X = Letter   

# = Number

Control boards/modules

90% of the boards are either White Rodgers or Honeywell.

White Rodgers PMMN nomenclature:  50X##–###

Examples:

50A50-209

50A55-120

Honeywell PMMN nomenclature:  S####X#### or ST####X####

Examples:

S8600C3003

ST9120C4057

The other 10% are UTEC Controls (United Technology), Johnson Controls, Robertshaw, Texas Instruments, etc.

Hot Surface Ignitors – Silicon Carbide

100% are Norton 201 or 271.

Norton PMMN nomenclature: 2#1 or 2#1X

Examples:

201

201N

271J

The PMMN will be stamped on the ignitor harness plug.

Hot Surface Ignitors – Silicon Nitride

100% are White Rodgers.

White Rodgers PMMN nomenclature: 768A-# or 768A-###

Examples:

768A-4

768A-845

The PMMN will be on a paper tag around the ignitor harness.

Gas Valves

98% are Honeywell or White Rodgers.

White Rodgers PMMN nomenclature: 36X##–### or 36X## type ### 

Examples:

36C03-333

36J24-205

36J24 type 205

Honeywell PMMN nomenclature: VX####X####

Examples:

VR8300A4003

VS820A1054

The other 2% are Robertshaw.

Robertshaw PMMN nomenclature: 7##–### 

Examples:

700-400

720-051

WORKING NOTES

forwardthinking.resideo.com/related_links/thermalsolutions/Application_Selection_Guide-63-9575.pdf

https://climate.emerson.com/documents/white-rodgers-product-catalog-en-us-1619412.pdf

https://webapps.emerson.com/wrproductselector/

Whoever is locating the replacement part should have access to all online dealer portals for the HVAC brands that you service. This is important for looking up current replacement parts and warranty information.

Manufacturers supersede replacement parts to newer models over time. Part manufacturers may develop and release new versions of existing parts without a significant reason. Occasionally, manufacturers supersede parts because the parts may have a design flaw or a high failure rate. These might not be dangerous or worthy of a recall, but the manufacturers quietly replace that part with a new one. Ever wonder why that inverter board on a 2-year-old system is a different part number? Depending on the age of the equipment, the manufacturer may have superseded the part several times.