Loss of Charge CGAM

Loss of Charge Function

Units may experience leakage of refrigerant charge at any point during their life.
Excessive refrigerant leakage negatively impacts capacity and reduces suction saturated temperatures, which can impact brazed-plate heat exchanger reliability.
The goal is to detect the condition and shut down the circuit before incurring any damage.

Loss of Charge Description

The circuit must have EXV superheat control. A circuit-level diagnostic, loss of charge, shall be called out if the following operating criteria has been met: Circuit is energized.

Suction superheat (suction temperature minus saturated suction temperature) is greater than 5°C (9°F).
Leaving water temperature is less than 15°C (59°F).
EXV Flow Command is more than (1.75 * Compressor Flow Estimate) for 5 continuous minutes. See Superheat Control Algorithm specification for definition of EXV Flow Command and Compressor Flow Estimate.

Validate MP software on controller is up to date
Single Circuit
1. Verify chiller has no leaks
2. Validate suction temperature sensors for accuracy. Should be +/-1F
3. Validate suction pressure transducers for accuracy. Should be +/-1 psi
4. Validate EXV operation by taking manual control to ensure it is not sticking or binding
5. Validate Charge (see below)
Both Circuits (likely flow issues)
1. Validate water flow and flow switch match submittal data
2. Validate pressure drop across the BPHE matches submittal data
3. Ensure there are no upstream valves that are closed
Make sure ∆T is set appropriately to the ACTUAL ∆T

CHARGE VALIDATION:

Refrigerant charge can be verified by looking at full load subcooling using the following criteria:

Validate chiller water flow matches submittal data (reference CGAM-SVB04A-EN)
All compressors on and all condenser fans running with clean condenser coils
An additional check of charge can be done by monitoring EXV Percent Flow Command and Superheat Control Compressor Flow Estimate in Kestrelview for the respective circuit. When properly charged, the ratio of EXV Percent Flow Command/Superheat Control Compressor Flow Estimate should be 1. If the ratio is 1.5 or greater, suspect low refrigerant charge
Flashing in the EXV Sight Glass may also be a good indication of low charge in a circuit.
Updating the main processor software to version 6.0 or newer may help eliminate nuisance low evaporator refrigerant temperature diagnostics as well. An enhancement was implemented which helps when rapid changes of suction superheat is observed at start up causing EXV to pinch down starving the evaporator as a result of interpreting this situation as carryover (liquid through the compressors).

ROUND TUBE/ LANCED ALUMINUM FIN CONDENSER COILS:

Subcooling should be between 15-20F when properly charged
EXV position should be around 40-60% open at full load, ALL compressors running on a given circuit, and controlling suction superheat to approximately 12F

MICROCHANNEL CONDENSER COILS:

Subcooling should be between 12-14F when properly charged
(CGAM built with micro channel condensers will have slightly lower full load subcooling)
EXV open slightly more than the 40-60% seen with round tube/aluminum lanced fin design.

The loss of charge diagnostic is generated when the RATIO:

EXV % Flow Command/Superheat Control Compressor Flow Estimate is 1.7 or greater.

Worksheet attachment below for calculating Ratio. Click on "enable editing" to be able to populate the values.

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
- Service Bulletin: CGAM-SVB04A-EN
Other:
- N/A

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