APRIL 1999

Troubleshooting compressor motor faults

Problem: A compressor failure in an HVAC/R system is often caused by an electrical fault. What's the best way to check a compressor for electrical problems?

Solution: Fluke Canada suggests this procedure. Remove the electrical terminal cover and check the following external connections using a voltage and current meter. A clamp meter makes the job easier. Note: When doing measurements on compressors with internal thermal motor protection devices that have been running extremely hot, give the compressor time to cool down prior to the electrical test to allow all the devices to reset to their normal positions.

1. Check the line voltage at the load centre with the compressor off. Low line voltage causes the motor to draw more current than normal and may result in overheating and premature failure.

Line voltage that is too high will cause excessive inrush current at motor start, again leading to premature failure.

2. Check the line voltage at the motor terminals with the compressor running. The voltage should be within 10% of the motor rating.

3. Check the running current. The readings should not exceed the manufacturer's full load rated amps during heavy load periods. Low amps are normal during low load conditions. Excessive current may be due to shorted or grounded windings, a bad capacitor, a faulty start relay, or an indication of excessive bearing failure.

Use rope and pulley action of chain to reconnect broken links

Here's a useful tip that my partner and I came up with when we were faced with a broken drive chain. Time was of the essence in the sawmill, and every minute the machine is down, money was lost. The following method is useful when time is tight and proper tools are unavailable.

Problem: The chain drive was too tight to put a connecting link in by hand. But it would take too much time to loosen the drive unit to gain the bit of slack need-
ed. And no mechanical chain tightener was available.

Solution: To gain the slack needed, try to make use of the chain's natural ability to become a pulley system. Take a suitable size and length of rope and tie it to a link back from the free end of the chain. Then weave the rope in and around the chain links. Pull the rope tight--by using the rollers as pulleys you gain a mechanical advantage. This gives you the slack needed to connect the chain. It also works well on drives with long centres.

Mr. O's thanks--and Problem Solver T-shirts--go to Wes Larose, lead millwright, and Denis Cayouette, production millwright, at the Tembec Sawmill in Cochrane, Ont. Their tip also is now entered in our Best of Mr. O Problem Solver Tips contest.