Signs a chiller compressor is heading for failure
Compressors rarely fail without notice. The warnings are mostly in readings and sound, and they usually appear weeks ahead.
A compressor is the most expensive single component in most chiller plant, and the one that gives the clearest advance warning. The warnings are easy to miss because none of them stops the machine.
What to watch
- Rising current draw at comparable load. The machine is doing the same work for more power. Often the first measurable sign.
- Repeated high-pressure trips. Especially in the afternoon. The compressor is being asked to work against a condensing pressure it was not designed for.
- Oil condition and level. Darkening oil, acidity, or level that will not hold. Oil analysis is inexpensive relative to what it predicts.
- Short cycling. Starting is the hardest thing a compressor does. Frequent starts shorten life quickly, and usually point at controls or a sizing mismatch rather than the compressor itself.
- Noise and vibration changes. A new rattle, knock or pitch change is worth investigating the day it appears.
- Superheat and subcooling outside band. Points at charge or metering, both of which damage the compressor if left.
Why the root cause is usually elsewhere
Most compressor failures are secondary. Something else — a fouled condenser, a failed fan, low charge, a sticking expansion device — puts the compressor into a duty it cannot sustain, and it eventually fails. Replacing the compressor without finding that cause buys a repeat of the same failure.
What to do with the warning
Log the readings, find the cause, and decide deliberately whether to repair or replace. That decision is much easier made in spring with a trend in hand than in August with a building warming up.