Depending on the types of systems you regularly service and install, you might not see many discharge line mufflers. These are generally found installed on larger systems, as noise generated from smaller systems may not be as problematic. 

The muffler reduces noise from gas pulsations by allowing the gas to expand inside the muffler chambers. Some mufflers will also have internal baffles, which are designed to further dampen and smooth out the low and high frequencies of the vapor leaving the compressor. 

Some discharge line mufflers may look like a filter drier, but they are definitely not, and installing a typical filter drier in the discharge line can be quite problematic. 

The gas pulsations can cause the desiccant to break apart and plug up the screens within the filter drier or, even worse, be released into the piping and contaminate the system. To that end, be sure never to install one on the discharge line.  

If you ever need to replace a discharge muffler, make sure you confirm it is a muffler and not a filter drier. A possible quick test is tapping its side — if it sounds hollow, it is probably a muffler. If it sounds solid, it is most likely a filter drier. 

A muffler can be added to an existing system. When selecting a discharge line muffler, select one with a connection size that matches or exceeds the discharge line size. A larger muffler may remove more pulsations due to its larger internal volume.  

Mufflers are designed to be installed directly after the compressor, and before an oil separator if one is used. Always follow the installation instructions from the manufacturer. Some may have specific directions on mounting and orientation to prevent oil from collecting inside the muffler.  

Discharge line mufflers may not always eliminate noise created from vibration. If vibration noise is still an issue, a vibration eliminator can be installed between the compressor and the muffler. If a vibration eliminator is used, the discharge muffler may need to be supported on each end due to the size and weight of the muffler.  

On multiple compressor systems, such as supermarket racks, a single muffler may be installed on a common discharge line of the rack or installed on each individual compressor. 

While it is very unlikely, if a muffler were to become clogged, you may see elevated condensing temperatures, increased compressor amp draw, and in severe cases, compressor overheating or tripping on high pressure. To prove this issue, first see if there is an extreme temperature drop across the muffler and then measure the pressure entering and leaving. Again, it is very unlikely you will come across this service issue.