[Leak] Check, Please

  • October 3, 2019
  • Len D'Amico

As you go about your day, it begins to register that it’s getting warmer and more humid in your building. Perhaps there is warm air blowing out of the grills, or you notice ice and/or water around the indoor unit. Since it’s sweltering outside and your colleagues are getting testy, you ask your HVAC service provider for priority service. After the diagnosis is complete, the technician tells you the system is “low on refrigerant”.

Depending on the size and location of the cooling equipment and the amount of refrigerant “missing”, the tech can often add enough refrigerant to get the system back up and cooling – a short term fix that some call a “gas and go”. But you’re not out of the woods; several things must be considered to determine the best course of action to effect a longer-term solution. And the most likely result requires a “leak check and repair”. 

Refrigerant leaks can be notoriously difficult to find and sometimes impossible to repair. First and foremost, it is imperative to know the capacity of the refrigerant circuit of the equipment in question; that is, the amount of refrigerant the circuit was designed to hold. The technician should be able to provide this information, regardless if the equipment in question is a packaged or split system.

If the system is a packaged unit, the refrigerant capacity is listed on its tag. But for split systems, the technician must calculate and add the amount of refrigerant which fills the copper refrigerant lines that connect the indoor and outdoor units. Since the distance between the two units can vary, the amount of refrigerant also varies.

When the HVAC tech takes the pressures of the refrigerant in the copper refrigerant lines – named the liquid and suction lines – it provides a fairly good idea of how much refrigerant is left in both. That information, coupled with how much refrigerant the circuit should hold, allows the tech to provide an estimate for the cost of the replacement refrigerant.
Once the cost of the replacement refrigerant is known, an estimate of the labor to find and repair the leak is needed. But without knowing the exact location and nature of the leak, it’s almost impossible to determine the time it might take to find what can sometimes be a needle in a haystack.

Fortunately, there are several procedures we may use to leak check a system, and a judicious use of techniques can minimize the amount of labor, and therefore the cost.

First, a visual inspection should be done. Sometimes there is a loose cap on an access point. After tightening it, refrigerant may then be added to the circuit to bring it to the proper pressure. This is the best case scenario and will result in the lowest possible cost to the customer.

The visual inspection should also include looking for the presence of oil, an indication of the location of a refrigerant leak. Oil is naturally present in the refrigerant circuit. Oil under the compressor or the fittings that connect the refrigerant lines to the indoor and/or outdoor units are the most common places to look for that oil.
If the visual inspection does not indicate the location of a leak, sometimes a tech will add a little refrigerant to the circuit. This is sufficient to raise the pressure enough so that the tech can hear a hiss – the refrigerant escaping from the circuit. (See ultra-sonic leak detectors below.)

If the leak has not been found after a visual inspection, there are additional techniques that can be used.
Some HVAC companies employ ultra-sonic and bubble leak detectors; with the latter, the tech may apply a viscous liquid soap to all accessible piping at the condenser and air handler and check the accessible areas of the air handler’s coil. Bubbles form where the gas is escaping from the copper piping. Ultra-sonic leak detectors translate a hissing sound (the sound of the escaping refrigerant) that can be heard through headphones.

Another approach to be considered when the source of the leak is not easily identified is adding dye to the refrigerant circuit while at the same time adding refrigerant. The customer will have temporary cooling and the labor is minimized looking for what can be a hard-to-find leak. A return visit is then scheduled a few days later when the use of UV lights will determine the source of the leak. A strategy for repairing the leak is then determined.

Another technique used is to pressurize the system with nitrogen after reclaiming and preserving the refrigerant left in the circuit. This is time-consuming and labor-intensive and should only be done when absolutely necessary.

Depending on the cause of the leak, refrigerant may have to be completely reclaimed from its circuit in order to allow the repair to be done. The refrigerant can be preserved and re-used when the system is charged after the repair of the leak.
Finding and repairing leaks in an HVAC system can be difficult, but your HVAC vendor should be able to provide you with various options to ensure you are kept in the loop and understand the strategies for keeping the cost down.

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