Knowledge Base Search

Chiller Phase Reversal - Poor Cooling and Pumping performance

SUMMARY
This article describes how to repair a chiller system that is currently having cooling or pumping problems.

SYMPTOMS
Scroll compressor running but is loud with poor cooling and pumping performance.

CAUSE
At startup: This condition commonly occurs at startup. When the chiller is run tested at the factory, there is a 50% chance that your building power will be orientated the same as the factory. If your building is out of phase with the chillers factory orientation, all three phase components, such as pumps and scroll compressors WILL run backwards.

After initial startup: It is possible for a chiller to begin running backwards if ANY two legs of main supply power are reversed at any time. Common items that can cause this are: Replacement of a breaker, replacement of a main or sub electrical distribution panel.

RESOLUTION
Other than abnormally loud Scroll operation, there is no way to physically confirm that a scroll is turning in the wrong direction. Using commonly available test equipment however, this can be easily confirmed by:

1. Checking the chiller suction and head pressures. If your scroll is running in reverse, you can expect higher than normal suction pressure and lower than normal head pressure.

2.Using an amp clamp, the compressors amp draw will be abnormally low.

Note: The specific reading you can expect have not been provided since the values will vary greatly depending on operating conditions. The factory recommends using readings taken as part of startup or maintenance for an operational baseline.

Another indicator of a phase reversal would be your pump. Using a nylon wire tie you can CAREFULLY insert the pointed end of the tie into the pump motors air fan towards the back of the pump motor. If the tie end goes up, the pump is turning clockwise (CW) and of the tie end goes down the pump is turning counter clockwise (CCW). On the stainless steel pump housing, there is an embossed arrow indicating proper rotation. Using the confirmed pump rotation, you can determine if the pump is rotating the proper direction – or not. Since all three-phase components are designed to run the same direction, there is a very good chance if one component is running the wrong direction they all are.

How to correct phase reversal: Reverse any two legs of main supply power entering the chiller. This can be done at the breaker, service disconnect or at the chillers high voltage single point wiring connection.

NOTE: RUNNING A SCROLL COMPRESSOR IN REVERSE WILL CAUSE DAMAGE TO THE SCROLL.

APPLIES TO
ALL THREE-phase models

Posted 1/30/2006 :: 10628 views