American Standard: what you can keep on an A2L swap
Checked against R454B Application Guide — AC Condensing Unit and Heat Pump (SSC-APG020A-EN), September 2026.
American Standard answers all three questions, and two of the answers are the ones a homeowner least wants to hear. The coil goes: its R454B Application Guide states that an R-410A evaporator coil cannot be used with R-454B or converted to it. The line set is the interesting one, because the trap runs the opposite way to everybody's assumption — R-454B is rated on *smaller* copper here, so the danger is that the line you own is too big, and an oversized vapor line is named in the guide as a compressor reliability risk rather than a harmless margin. And the furnace is not replaced but is not left alone either: the refrigerant detection sits in the coil, on every coil, with a factory-supplied wire harness to the furnace that somebody has to land on site. That last one is the clearest example on this site of two manufacturers answering the same A2L question differently, because Carrier does not put it there. Two documents are read for this brand: the September 2024 transition bulletin, which covers American Standard Heating and Air Conditioning and Ameristar together, and the R454B Application Guide, which speaks for the whole single-stage R-454B range by tonnage. Its two heat pump families and three Silver air conditioner families are here with the R-410A model each one replaces. No model-level document has been read for any of them, so every family is a row rather than a page — the answers above are the brand's, and they are the same for all five.
The three answers
Indoor coil
Has to be replacedYour existing R-410A coil cannot stay. American Standard states it directly: an R-410A evaporator coil cannot be used or converted with R-454B, and the R-454B coil has to be factory equipped with a mitigation control board.
Line set
Can stay, with conditionsSometimes — and the trap here is the opposite of the one people expect. American Standard rates its R-454B units on *smaller* copper than R-410A, so the risk is that the line you own is too big rather than too small.
- The vapor line is the rated size for your tonnage or one of the listed alternates. A line that was acceptable on R-410A may not return oil to the compressor on R-454B, and an oversized vapor line is named as a compressor reliability risk rather than a harmless margin.
- The liquid line is 5/16 inch or the approved 3/8 inch alternate. A 1/2 inch liquid line is not approved at any tonnage. Every R-454B tonnage in the guide is rated on the 5/16 inch line.
- The run is inside 150 equivalent feet, and inside the vertical limit for the machine: 150 feet with an air conditioner above the indoor coil, 50 feet with a heat pump above it. 150 equivalent feet is the maximum the guide gives for a single-stage R-454B unit of this brand.
- The connection is checked separately from the size: copper of the right diameter can still be the wrong fitting. The single-stage heat pumps have new service valve connection sizes.
Furnace
Can stay, with conditionsYour furnace is not replaced, but it does not come away untouched: a new factory-supplied wire harness runs from the detection system in the coil to the furnace and has to be connected in the field.
- The new wire harness between the coil's refrigerant detection system and the furnace is connected on site. American Standard supplies the harness; the installer has to land it.
- Your furnace has to be one the harness can be connected to. The bulletin does not list which furnaces those are.
What to ask your installer about any American Standard swap
- Which indoor coil are you fitting, and what is the AHRI certified reference number for that combination?
- Are you reusing my line set, and how will you prove it is clean and holds a pressure test?
- Which mitigation kit does my furnace need, and is it in the quote?
The documents behind this
ManufacturerA Refrigerant Detection System is added to the coil product family. It contains a leak detection sensor and a mitigation control board mounted to the coil, and a new factory-supplied wire harness runs between the system in the coil and the furnace, requiring field connection.
ManufacturerR-454B coil model numbers change in the 1st, 9th and 14th digits, and some models also change in the 6th, 7th and 8th.
Our readingBecause the changed digits sit at the start, the middle and the end of a fourteen-character number, a coil number that looks almost identical to yours can be for the other refrigerant. Read it character by character.
ManufacturerOutdoor products carry a 5 in the first digit of the model number to identify the new refrigerant, where the R-410A equivalent carried a 4.
Our readingThe bulletin's own heat pump table shows one family where that is not how it reads: the Ameristar A4HP5 becomes the A5HP5, so the 5 is the second character and the first stays an A. Someone checking only the first digit of that model would conclude their unit is not in the table.
ManufacturerThe single-stage R-454B heat pumps have new compressors, new service valve connection sizes, and new TXV and refrigeration designs optimised for the new refrigerant.
ManufacturerThe bulletin covers American Standard Heating and Air Conditioning and Ameristar by American Standard together, and says it will be updated as more R-454B products are released.
ManufacturerAn R-410A TXV or evaporator coil cannot be used with R-454B refrigerant, and cannot be converted to it. The R-454B coil has to be factory equipped with a mitigation control board. This is the sentence the 2024 transition bulletin did not contain, and it is why the coil verdict on this brand is now replace rather than unknown.
ManufacturerR-454B line sets have a smaller rated liquid and vapor line than R-410A, and the allowable lengths and vertical lifts may be shorter. Refrigerant velocities are slower, so a vapor line that was acceptable on an R-410A system may not provide proper oil return on R-454B. An oversized vapor line is called out as a compressor reliability risk, not a harmless margin.
ManufacturerEvery R-454B tonnage in the single-stage range is rated on a 5/16 inch liquid line, with 3/8 inch as an approved alternate and 1/2 inch not approved at any tonnage. The rated vapor line runs 5/8 inch at 1.5 tons on a heat pump and 3/4 inch on the air conditioner, 3/4 inch from 2 to 3 tons, and 7/8 inch from 3.5 tons up — except the 5 ton air conditioner, which is rated on 1-1/8 inch on the 14 and 15 SEER single-phase models and 7/8 inch on the rest.
ManufacturerA single-stage R-454B air conditioner or heat pump has a maximum line length of 150 feet. Above the indoor coil, an air conditioner is allowed 150 feet of vertical separation and a heat pump only 50. A crankcase heater is recommended beyond 60 feet, a TXV is required beyond 60 feet where the coil uses a piston, and beyond 150 feet compressor oil is added at 2 ounces for every 10 feet.
What replaces what: the American Standard A2L range
Every American Standard A2L outdoor unit on this site, and the R-410A model it replaces. This is the table that today exists only inside a PDF. The last column says which document each row was read from; a model in either column links to its own page once a document about that model has been read.
| A2L model | Type | Tier | Compressor | Region | Replaces | Data read |
|---|---|---|---|---|---|---|
| 5A7A3 | Air conditioner | Silver 13 Air Conditioner | — | — | 4A7A3 | service bulletin, spec sheet |
| 5A7A4 | Air conditioner | Silver 14 Air Conditioner | — | — | 4A7A4 | service bulletin, spec sheet |
| 5A7A5 | Air conditioner | Silver 14 Air Conditioner | — | — | 4A7A5 | service bulletin, spec sheet |
| 5A6H4 | Heat pump | Silver 14 Heat Pump | single-stage | — | 4A6H4 | service bulletin, spec sheet |
| 5A6H5 | Heat pump | Silver 15 | single-stage | — | 4A6H5 | service bulletin only |
This is a starting point, not an approval. Everything here is read from published manufacturer documents and dated, but only the licensed contractor who signs your installation can approve a specific system for your home and your local code. Take the citations on this page to them and ask.