6 Simple Steps to Troubleshooting a Compressor
The core of any refrigeration system is the compressor, and most of the troubleshooting that needs to be done when a system doesn’t work correctly boils down to this one piece of equipment.
Whether you’re an expert certified in HVAC systems or a DIY die-hard looking to repair a compressor system, the essential steps are the same.
Troubleshooting a Compressor: Is It Always The Same Process?
Although the steps are the same, the scale of the operation and the possible consequences of overlooking a step in the process may differ between compressors.
When you apply a methodical approach to troubleshooting a compressor, it helps eliminate opportunities to overlook the cause of the problem by ensuring that every aspect of the compressor’s operation is reviewed for issues.
When troubleshooting a compressor of a refrigeration system, there are really only 6 simple steps to follow.
1. Measure the Suction and Discharge Pressures
Since the job of the compressor is to move supercooled refrigerant from the evaporator to the condenser, checking for pressure problems is essential when diagnosing issues with the system’s operation.
Using standard refrigeration gauges is the easiest method, but you can also get a measurement using a digital multimeter and pressure module if you don’t have access to standard refrigeration gauges at the time of troubleshooting.
Keep in mind that the system will likely be under high pressure when setting and removing your gauges, and use safe refrigerant handling protocols to keep the system from losing refrigerant.
2. Check the Discharge Line Temperature
In addition to pressure, temperature measurements help you get a good idea what is going on inside of an air compressor.
Use the pipe clamp accessory on your DMM to get a measurement. 275 to 300 degrees Fahrenheit is the high side of the temperature range, above that, the performance of the compressor will suffer because the temperature will be high enough to destroy lubricant properties.
Since high temperatures can be caused by low refrigerant pressure, insufficient charge, or the intrusion of noncondensible gas in the system (among other things), this data point can be compared to other information like your pressure readings to rule out symptoms of these major sources of compressor performance trouble.
3. Record Temperatures in the Refrigerated Space
Another vital data point in your troubleshooting diagnosis is the temperature of the space needing refrigeration.
It’s important to understand the nature of the cooling system in use and the target temperatures the compressor should be attaining when recording this number.
Those factors will help you determine the extent of the compressor’s performance shortcomings, which also helps to confirm or eliminate hypotheses about the issue.
4. Perform a Compressor Valve Test
Use the following method when testing the hermetic and semi-hermetic pressures of compressors. Using the pressure module on your DMM, do the following:
- Connect the module at the suction line service port
- Close the compressor on the low side of the system by front seating the suction service valve
- Let it run for at least two minutes, but not more than three
- Turn off the compressor and take the reading
The compressor should pull around 15 inches of Hg. If the pressure displays around 10 or less, that means the discharge valves are likely leaking need replacements. If it does not pull below 15 inches of Hg, then the suction valves will likely need to be replaced.
For hermetic systems, this means replacing the whole compressor.
5. Checking for Compressor Electrical Motor Faults
Checking for failures in the compressor’s electric motor helps, especially if the system is accessible enough to allow for compressor repair without full compressor replacement.
Use a clamp meter to check both AC voltage and AC current. Make sure you check line voltage at the load center with the compressor off, as well as voltage at the motor terminals with the compressor running.
Line voltage that is too high will lead to premature failure, and too low will result in more performance issues.
This should be within 10 percent of the motor rating. Make sure you also check the running current and compare it to the manufacturer’s safe maximum amps.
6. Refrigerant System Problems
Sometimes mechanical problems are the core issue when compressors fail to function properly, but more often there are refrigerant system problems contributing to the issue in ways that cause the mechanical failure.
By replacing a compressor without checking for and fixing these issues, system failure will reoccur with the same basic symptoms.
Rule out these issues as when replacing or troubleshooting a compressor.
- Poor piping practices preventing oil from properly returning to the compressor while running
- High discharge temperatures creating acids that can damage the system
- Insufficient air flow to either the condenser or evaporator coil
- Low suction pressures
- Liquid refrigerant flooding back
Sometimes you can fix these issuesby replacing the compressor itself, like when a mechanical problem in the compressor causes low suction pressure. When the root of the problems are system design, though, the compressor replacement will necessitate changing some elements of the system’s function to get better long-term results.
The process of troubleshooting a compressor will reveal which aspects of the compressor’s operation are compromised. This is key to understanding how to fix those problems.
Be thorough, and document each measurement, because you often need the results of multiple steps to draw conclusions about the source of issues with the system’s performance.
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