How to diagnose & repair refrigerant leaks in the air conditioning or heat pump system
Leak repair tips for the HVAC cooling coil or evaporator coil
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This article discusses how to repair refrigerant leaks in air conditioning and cooling systems, using as an example, repairing a leaky or damaged air conditioning the cooling coil (evaporator coil) in the air conditioning air handler unit. Our photo at page top shows the cooling coil in the attic air handler component of a central air conditioning system.
If your air conditioning system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
How To Repair HVAC Air Conditioner Refrigerant Leaks
First we need an accurate diagnosis of the problem. If your air conditioning or heat pump system has lost cooling (or heating) capacity, there can be various causes besides loss of the refrigerant in the system.
If you know that the refrigerant level is low or zero, don't just re-charge the system. Find and fix the refrigerant leak. See REFRIGERANT LEAK DETECTION. While it's quick (and cheap) to just add refrigerant to a system, we were taught at HVAC school to scorn earning a living by developing a refrigerant gas delivery route.
An air conditioning or heat pump system is normally completely sealed and should never "use" refrigerant. Refrigerant gases are not a substance which is "consumed" in an HVAC system.
In an emergency, such as at a commercial establishment needing time to move frozen food, one might just add refrigerant, but the proper repair is to find and fix the refrigerant leak.
If the refrigerant gas leak is in a valve or access port, such as the service ports to which the HVAC technician connects her gauge set, the valves there may be able to be cleaned and salvaged, or the valves may need to be replaced.
Replacing a refrigerant gas service port valve is a soldering job similar to what we describe just below. In our AC repair career we never had to replace one of these valves but we did have to install them on some systems where they were not already in place.
Our photo at left shows refrigerant gauge access ports on a compressor/condenser unit.
If the refrigerant gas leak is in the air conditioning or heat pump copper tubing a repair should be easy - the damaged line is re-soldered using high silver content solder and a high temperature torch. (We used MAPP gas for silver soldering of copper fittings, some techs use Acetylene or other gases).
A damaged section of refrigerant line may need to be cut out and replaced. The repair is about the same regardless of whether the leak was in the larger diameter suction line or the smaller diameter high pressure line.
If the refrigerant gas leak is in the condensing coil or in the evaporator coil, repair might be possible, but we're less optimistic that repair is possible, but it might be, as we explain just below.
Guide to Repairs of an Air Conditioning or Heat Pump Evaporator Coil or Condensing Coil
Review the coil inspection, diagnosis, and repair tips at COOLING COIL or EVAPORATOR COIL. We find that the terms "cooling coil" and "evaporator coil" are used as synonyms in most cases. Sketch at left courtesy of Carson Dunlop.
Even if the cooling or condensing coil has a repairable leak, if the coil is badly damaged such as having all crushed fins, it may be best to replace it.
Damaged cooling / evaporator coil fins over more than 10% of the coil surface, blocking air flow may be a reason to replace the coil.
If the cooling coil or condensing coil is in good physical condition but it's dirty, it needs to be cleaned before it can be repaired. Spray-on coil cleaners are used by lots of HVAC technicians.
If the coil is dirty with moldy dust and debris and especially if the building is occupied by people at extra health risk, we don't like to see a coil cleaned by blowing it off with compressed air, as you're simply sending all of this moldy junk into the building. See DIRTY COOLING COIL and see Mold Growth in Air Handlers. You may also want to check out Leaks, Rodents In Air Handlers.
Next check the cooling coil or evaporator coil for visual evidence of refrigerant leaks. Visual evidence of a refrigerant leak on a coil may include stains from refrigerant oil left at the point of leakage. See REFRIGERANT LEAK DETECTION.
When the one or more places where the cooling coil or evaporator coil is leaking refrigerant gas have been found, it's time to decide if we can perform a solder repair of if the coil has to be replaced. We offer some suggestions just below at Guide to Evaluating Evaporator Coil or Condensing Coil Refrigerant Leaks
Guide to Evaluating Evaporator Coil or Condensing Coil Refrigerant Leaks and Deciding to Repair or Replace a Coil
Evaporator coil or cooling leaks or holes: if an evaporator coil is leaking (or also if the condensing coil is leaking) you'll find out pretty quickly as refrigerant will be lost and the cooling system will stop providing cool air.
You'll need expert diagnosis by an HVAC service technician. Sketch at left courtesy of Carson Dunlop.
How easily a cooling system refrigerant leak repair will be depends on where the refrigerant leak has occurred and what caused the leak.
If the cooling coil has a single point leak caused by some mechanical damage (one of our readers accidentally drilled a hole in his coil while trying to drill a drain hole in his air handler), it may be possible to find the hole and repair it using silver solder.
If the refrigerant leak is in copper tubing anywhere in the cooling or heat pump system that is not too close to an evaporator coil or condensing coil, it should be possible to solder a repair, then evacuate and recharge the cooling system.
If the refrigerant leak is in thin copper tubing that just melts when you try to solder it, as suggested by one of our readers, your technician may fabricate a copper sleeve that slips over the damaged tubing and is then soldered in place.
If the refrigerant leak is in copper tubing in or close to the cooling coil (or in a condensing coil) a solder repair is hard to complete because the heat of the soldering process tends to de-solder other nearby connections. It might be possible if the technician is very expert and if s/he knows how to keep nearby surfaces cooled (we've used a wet rag).
If the refrigerant leak is in an aluminum part, soldering aluminum is more tricky and may not be feasible. Ordinary procedures using a torch, for example, just melt the aluminum. Expert welders use inert gas welding methods.
If the refrigerant leak is due to severe corrosion anywhere in an HVAC system we're not optimistic that a solder repair is possible. The conditions that caused a corrosion-related leak are likely to have thinned and weakened other parts. The cost of an attempted repair may be wasted.
Replacement of the cooling coil (or condensing coil) is more often going to be recommended by your HVAC technician because of these difficulties.
Recharging the HVAC System after Refrigerant Leak Repair
In case you didn't realize it, in order to solder a repair in an air conditioner or heat pump piping, tubing, evaporator coil/cooling coil, or condensing coil, it will first be necessary to remove all of the refrigerant from the system.
The HVAC technician will connect a pump to pull a vacuum on the system to remove as much air, gas, debris, and moisture as possible.
The HVAC technician will probably want to install a refrigerant filter/drier (see our photo below) to remove any moisture that leaked into the system while it was open to the atmosphere, and perhaps she will install other filtration equipment on the system at this time. It's a good idea.
Installing a Dryer / Filter Unit on the Air Conditioning or Heat Pump Refrigerant Line
Once a system refrigerant leak has been repaired, it will be necessary to flush the refrigerant piping system (usually using nitrogen), pull a new vacuum on the system, and then re-charge the system with the proper type and quantity of refrigerant.
Before re-charging the repaired air conditioning or heat pump system with refrigerant, the technician will usually install a filter/drier such as shown in our photo at left.
While some technicians always install a filter/drier on the refrigerant system, often when we see one of these we assume that the system has undergone some service or repair as that's most often when the device is added.
In fact if the system was open and badly contaminated the HVAC technician may install a drier right after the repair and may install a new or second one on the same system a few months later.
Filtering the refrigerant liquid leaving the compressor/condenser protects the Thermal Expansion Valve or capillary tube from clogging.
Our photo at left shows that a Catch-All™ C-163_S refrigerant dryer and filter has been installed on the high pressure refrigerant line leaving the outdoor compressor/condenser unit. This is where we usually see this device installed. Notice that the refrigerant dryer, which removes un-wanted moisture from the refrigeration system, is labeled with the types of refrigerant with which it is designed to be used.
Replacing an HVAC Cooling Coil or Evaporator Coil
If the decision is to replace the cooling coil or the evaporator coil, be sure that the new coil is the proper size and shape to match the condenser or evaporator unit itself. See ADDING A/C: RETROFIT SIZING for an example of a mismatch that means poor heating or heat pump system operation.
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Thanks to to Guy Benfante, Chesapeake, VA 8/26/07 for the photograph of an ice-blocked air conditioning system evaporator coil and for his suggestion that we provide an air conditioning system troubleshooting FAQ.
Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
Thanks to reader Don Jackson for HVAC refrigerant leak soldering repair tips (Aug-Sept 2008).
Wikipedia provided background information about the definition of HEPA and airborne particle interception.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
More Information on Building Diagnostic Inspections and Repairs
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