Isolation Test – Detecting and Fixing Leaks in Your HVAC Equipment

Typically, air conditioning or refrigeration systems depend on refrigerants as their cooling medium. This can be the R-22 or the R410A based on the unit and how modern it is. The level of the refrigerant in an air conditioning is extremely important and as such should be checked oftentimes.

Technically, refrigerants are not used up in the cooling process and therefore their levels should remain the same. However, because of leaks, refrigerant levels tend to go down and this can cause a number of equipment anomalies including compressor failure, freezing of the evaporator coil, reduced efficiency of the air conditioner, or even wear and tear of your unit.

How to Identify and Fix Leaks

There are various types of leaks and approaches to identifying and fixing them. A majority of leaks are found through an electronic leak detector, visual examination, or a proprietary bubble solution. In the event none of the above methods are able to identify the leak, the nitrogen test is used. This is where nitrogen is pressurized into the refrigerant lines and then pressure-tested to identify leaks.

Ensure the nitrogen used is oxygen free because any traces of oxygen can easily explode when mixed with oil thus damaging your equipment or causing injuries to those in the vicinity.

When dealing with a sealed system which doesn’t allow you physical access to the various components which you suspect could be vulnerable to leaks, you have to dismantle the system into various components. Some of the sealed systems which warrant this treatment include in-wall condensers, concealed refrigerant lines, and in-wall evaporators.

Isolation Test

The isolation test refers to the process where the components of the system suspected of leaking are separated from the rest of the system for testing. In a typical nitrogen isolation test, the system being examined is isolated into 4 parts and these are:

  • The condensing unit
  • The suction line
  • The liquid line
  • The evaporator coil

Once the components are separated, they are fitted with access valves and then sealed before being pressurized with dry nitrogen. The advantage of nitrogen gas is that unlike refrigerants, it is not affected by temperature changes

However, at high pressures, nitrogen can cause serious injuries or even deaths. Because it is an asphyxiant, nitrogen can also suffocate you when in high concentrations. It is therefore important to follow the guidelines and the pressure testing procedure carefully.

The Testing Procedure

The first step is to ensure any residual refrigerant left in the system to be tested is recovered before the procedure can begin. The nitrogen cylinder should be carefully secured or located at a position where it cannot fall over.

The cylinder should then be fitted with a regulator and a manifold hose. The isolated sections to be tested should be fitted with pressure gauges.

Slowly pressurize the system by winding the nitrogen regulator in a clockwise direction. The pressurizing process should be done in stages not exceeding 45 psi at a time. Only the relevant sections of the system should be pressurized and this should be within their maximum allowable pressure.

Normally, the equipment will have a label indicating the maximum allowable pressure. Just in case it doesn’t have, the type of refrigerant can give you an idea on the maximum pressure. For instance, R22 systems should not be pressurized beyond 350 psi while R410A systems should not be pressurized beyond 478.6 psi.

At every pressure increment, listen for any audible pressure loss. You can also check the gauge for any instances of pressure loss. Every nitrogen cylinder is to be used with a suitable regulator. The regulator comes with an output limiting device so that the system is not over-pressurized.

Where a leak has been identified, the dry nitrogen should be vented and then the leak repaired before the procedure is repeated. When you get to the maximum allowable pressure for the system, close the cylinder the manifold valve. The pressure shown on the gauge should be carefully noted and then the nitrogen regulator valve carefully removed as well as the hose.

The system should be maintained at the maximum allowable pressure for the entire duration of the test. Then, using a leak detection spray or even soapy water, test each joint for possibilities of leak points. If you identify the leak, vent the remaining nitrogen before you start the repair process. The easiest way to repair the leaks is by soldering them with aluminum, copper, or steel.

Once all the leaks have been established and sealed, the nitrogen can now be evacuated completely from the system and recharged with the appropriate refrigerant.