R-22 split system air conditioners and heat pumps are increasingly being retired (rather than repaired) as they near the end of their useful service lives. The most commonly used refrigerant in replacement air conditioners and heat pumps is R-410A.

This month's Tech Tip offers an overview of some of the issues related to R-22 and -410A in the field: operating pressure differences, oil characteristics, and temperature glide.

Operating Pressure Points

One of the most well-known characteristics of R-410A is its operating pressure. Split systems that use R-410A operate at higher pressures than R-22. Because of this, tools used by technicians during service, installation, and troubleshooting calls - refrigerant hoses, manifolds, and gauges - must be rated for these higher pressures.

Most new tools are designed to handle high-pressure refrigerants; old tools may not be. Do you know if yours are?

In addition, service and installation technicians need to make sure that their recovery machines were designed for use with R-410A. Replacement components such as TXVs also must be designed to operate with 410A.

Here's something that is obvious but critical: R-410A is not a drop-in replacement for R-22. R-22 equipment designs cannot accommodate the higher pressures of R-410A. Not only would the new, higher-pressure refrigerant cause the old, lower-pressure-designed system to break down in short order, it would also create a dangerous situation for the next service person who came to look at the unit.

Out With The Old Oil

As we pointed out last month, polyolester (POE) oils used with 410A absorb moisture, making them much less forgiving of service shortcuts than were the mineral oils used with R-22. Air in the system leads to moisture, and with a POE in the system, moisture leads to acid and sludge.

In addition to the service practices we pointed out last month, such as installing the correct filter-drier (100 percent molecular sieve) and following careful line soldering practices, there are further considerations for replacement work.

  • For instance, if the customer's existing line set is going to be reused, make sure you remove as much of the mineral oil as possible from the system before installing the new 410A unit. You also need to confirm the line set's correct size.

  • System manufacturers have also pointed out that although evacuating to 500 microns removes moisture from an R-22/mineral oil system, it will not remove enough moisture from a system using POEs.

    Troubleshooting With Glide

    Technicians used to working with R-22 systems may be unfamiliar with the temperature glides of R-410A.

    What this means, in essence, is that at a given pressure, the temperature at which a saturated vapor starts to condense (dewpoint) is higher than the temperature at which a saturated liquid starts to boil (bubble point). This temperature difference is called temperature glide.

    Because of this, pressure-based rules that work with R-22 do not work with R-410A. The good news is that R-410A's temperature glide is smaller than 0.2 degrees. System manufacturers agree that 410A behaves so similarly to R-22 in this respect, for small leaks, R-410A can be topped off.

    Use your best judgment, and when in doubt, always contact your equipment manufacturer or technical rep before proceeding.

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