Let us look at the aspects of air conditioning installations and in particular R22 versus R410a.

We find in industry, that a large percentage of air conditioning systems are still running on R22, of course all of the new systems are now running with R410a.

The reason for the change is the R22 is a HCFC. The phase out of CFC / HCFC based refrigerants began in 1995 and the manufacturers are following national and international protocols and trends in the phase out of R22.

R410A is an azeotropic blend comprised of 50% R32 and 50% R125. You will experience the problem of temperature glide with R410A which necessitates liquid phase charging. The glide is small (Less than 0.17K).

R410A is Non-toxic and Non-flammable but use in a well-ventilated area. Leakage in an airtight room creates risk for oxygen starvation accidents.

In the case of R410A coming in contact with fire a poisonous gas is given off. R410A saturated vapour pressure is approximately 60% higher than that of R22.

The composition of the refrigerant and the increased pressures necessitate R410A dedicated tools and procedures.

Looking at the following diagram illustrates an example of typical air-conditioning parameters for R410a.

 

With regards to what constitutes good practice we find the following changes.

As you will need to make several changes let’s start with the most obvious. You will need a dedicated R410A manifold gauge set or a set designed for multi gases including R410a. The charge lines and gauges themselves are made for the higher pressures generated by R410A. In addition, the charging lines have a nylon coating for HFC resistance. It is important to note that to prevent possible accidental use of inappropriate manifold gauge sets on R410A systems the service port size and charging line fittings have been changed from 1/4” to 5/16”.

The second consideration when using R410A is that the copper tubing requirement has changed to deal with the increased pressures. The use of R410A necessitates the use of seamless copper tubing. In addition, the wall thickness has been increased.

The table below illustrates the R410A seamless copper tubing requirement.

Diameter of tubing Minimum wall thickness (R410A)
¼” (6.4mm) 0.80 mm
3/8” (9.5mm) 0.80 mm
½” (12.7mm) 0.80 mm
5/8” (15.9mm) 1.00 mm

The third change lies in the flare nut sizes. The width of the flare nuts to be used with R410A has been increased as follows:

Diameter of tubing Flare nut width for R22 Flare nut width for R410A
¼” (6.4mm) 17 mm 17 mm
3/8” (9.5mm) 22 mm 22 mm
½” (12.7mm) 24 mm 26 mm
5/8” (15.9mm) 27 mm 29 mm

Whilst I am on the subject of flares, flare nuts when used particularly with R410A require the use of a torque wrench when tightening. The manufacturer of the unit will give the torque values in the installation manual. The following instructions are supplied with the torque wrench.

This torque wrench has various sized interchangeable open spanner type heads and the torque setting is determined and adjusted.

The fourth point is in the area of evacuation. On discussing the matter with various suppliers, I found that the method most desirable is the triple evacuation method. The steps are as follows:

Step 1: Evacuate the system to 2000 microns.

Step 2: Break the vacuum with nitrogen to 100 kPa.

Step 3: Release pressure and draw vacuum to 1000 microns.

Step 4: Break the vacuum with nitrogen to 100 kPa.

Step 5: Release pressure and draw vacuum to 500 microns.

Conduct leak rise test.

Note: Always use a regulator on a nitrogen cylinder. Your vacuum pump should have a non-return valve installed on the inlet.

Of course, this implies that your vacuum pump should be able to draw the required vacuum. Test your pump as follows.

Step 1: Visually inspect vacuum pump mechanically and electrically.

Step 2: Visually check the oil in the sight glass for level and colour. Should the oil be whitish (Moisture) or black (Carbon deposits), replace.

Step 3: Connect vacuum gauge, open necessary inlet valves and turn on vacuum gauge and pump. The vacuum pump should draw a vacuum of 500 microns or less.

Note: If after 2 minutes the pump is unable to draw 500 microns, replace oil. Should the pump still be unable to

draw 500 microns, overhaul or replace.

The suppliers of the R410A units are recommending a rising leak test, using nitrogen, proceed as follows:

The fifth point to remember is that R410A is a azeotropic blend and the refrigerant must be charged from the cylinder in liquid phase. These units tend to require critical charging by mass.

Looking at lubrication we find that mineral oil and HFC refrigerants are not soluble, therefore R410A requires the use of ester oil. This oil is hydroscopic. (Moisture is readily absorbed.)

Oil returning performance drops.

Lubricating performance drops as chlorine has a lubricating feature.

This explains one of the reasons why evacuation and dehydration have received so much attention.

Note: You should purge with nitrogen when brazing copper tubing; this prevents oxidisation of the internal surfaces and contamination of the system.

REFERENCES:

Thanks to: ACRA

Grant K Laidlaw

Grant Laidlaw F.S.A.I.R.A.C