Low Suction Superheat CGAM

Issue:

Low Suction Superheat Diagnostic

• Typical design superheat is 12F with chiller running at full load conditions.
• Superheat will vary depending on the conditions.
• The Low Suction Superheat Diagnostic is annunciated when the measured suction superheat stay below 3.96F for 1 continuous minute. If it bounces up and down at the threshold, the 1 minute timer resets.

Suction Superheat Description

• Superheat is the difference between suction temperature and saturated suction temperature.
• A temperature sensor measures suction temperature, and saturated suction temperature is derived from the measured suction pressure.
• The superheat control maintains a small, desired amount of superheat by moving the EXV, which adjusts the flow of the two-phase refrigerant into the evaporating heat exchanger.
• Excess liquid refrigerant in the suction is harmful to the compressor, and a deficit of liquid in the suction-side heat exchanger is inefficient.

Resolution:

1. Validate MP software on controller is up to date
2. Check circuit that is in alarm for a tripped compressor circuit breaker.
   1. There are two types of breakers that are used on CGAM Chillers. Either there is a dial to adjust the breaker or it is fixed and not adjustable.
      1. If it has a dial, it should be set to Maximum position.
   2. If it is at Maximum or if the breaker is fixed and it trips, the technician should use an amp probe to see what the compressor amp draw is relative to the rating on the compressor.
      1. If the rating is below the RLA for the compressor and the trips are intermittent, the breaker should be replaced.
   3. NOTE: On CGAM units there is no feedback to the controller (Dynaview) since the chiller is not equipped with current transformers (CTs).  There is no way for the control to determine if the compressors are drawing current.  
3. Validate suction temperature sensors for accuracy. Should be +/-1F
   1. Use thermocouple and compare temperature versus panel temperature
4. Validate suction pressure transducers for accuracy. Should be +/-1 psi
   1. Check panel pressure versus gauge pressure
5. Validate EXV operation by taking manual control in Techview to ensure it is not sticking or binding
   1. Validate movement by looking in the sight glass
6. Validate the chiller/circuit is not over charged (see Loss of Charge Diagnostic CGAM )

Notes:

Resource Available:

• Tech TV Video(s):
  • N/A
• Reference Literature: (Electronic copies can be pulled from e-library at Trane Residential (tranetechnologies.com))
  • IOM: CG-SVX17M-EN
  • Service Guide: CG-SVG002E-EN
• Other:
  • N/A

Changes:

Other Question/Problem/Cause Statements:

• Low suction superheat diagnostic?
• Low superheat
• Low suction superheat
• Superheat diagnostic
• What can cause circuit breaker to trip?
• Compressor shows running but is not running.
• Why does my DynaView show my compressor is running when it's not?
• My compressors do not run, why?
• My compressors don't run, why?
• Why do I have low superheat when my compressors are not running?

Facts:

• Air-Cooled Chiller (Pueblo) (CGAM 20-130 Ton)

Original HUB Document: DOC-102096

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.