Cooling Performance Troubleshooting

Temperature not reaching setpoint? Five root causes systematically diagnosed: viscosity, thermal conductivity, icing, pump flow, and heat exchange area. 7 real cases analyzed in depth.

5 Root Cause Analyses7 Troubleshooting Cases5-Step Diagnostic Process

Cooling Performance Troubleshooting

Temperature not reaching setpoint? Five root causes systematically diagnosed: viscosity, thermal conductivity, icing, pump flow, and heat exchange area. 7 real cases analyzed in depth.

5 Root Cause Analyses7 Troubleshooting Cases5-Step Diagnostic Process

The Nature of Cooling Difficulties

"Temperature not reaching the design setpoint" is one of the most common problems in coolant systems. Its essence is insufficient system heat exchange capacity, which may be caused by coolant physical properties, system design, equipment configuration, operating conditions, and other factors. Blindly replacing the coolant often fails to solve the problem and may even worsen it due to property differences.

According to 2025 case statistics, cooling difficulty problems involve multiple products including LM-4, LM-8, LM-11D, LM-11F, and LM-445. Root causes include viscosity increase, thermal conductivity differences, heat exchanger icing, insufficient pump flow, and excessive concentration.

Cooling DifficultyFive Root Causes

Root Cause Type	Typical Symptoms	Products Involved	Key Parameter Changes
Viscosity increase causing insufficient flow	Setpoint not reached, pump current changes	LM-8, LM-4	7.5% viscosity increase = 7.5% resistance impact
Thermal conductivity difference	Cooling degradation after coolant replacement	LM-11F, LM-11D	Thermal conductivity halved = sharp capacity drop
Local heat exchanger icing	Plate heat exchanger iced, cold cannot transfer	LM-8, LM-11D	Evaporation temp too low causes surface icing
Pump/flow rate issues	System temp differential too small (1-1.5C)	LM-4, etc.	Low end-load, excessive pump flow
Insufficient chiller heat exchange area	Cannot cool beyond certain temperature	LM-445, LM-8	Insufficient area or pump flow

SystematicTroubleshooting Steps

Verify Pump Flow Rate

Check pump operating current and frequency to confirm actual flow meets design requirements. Increased viscosity may cause insufficient flow - evaluate whether pump adjustment or frequency reduction is needed.

Thaw Then Cool Gradually

If plate heat exchanger is locally iced, raise temperature above 0C to melt ice, then reset target temperature and cool gradually. Avoid directly setting extremely low temperatures that cause re-icing.

Check Concentration

Excessive concentration significantly increases viscosity and affects flow. Appropriately reducing concentration can improve fluidity. Freezing point selection should have a 10-15C safety margin - no need to over-pursue low freezing points.

Compare Coolant Properties

Compare thermal conductivity and viscosity of old and new coolants. Calculate the impact of viscosity on resistance and heat exchange (7.5% viscosity increase = 7.5% resistance impact, 1.5% heat exchange impact) and determine if within acceptable range.

Check Chiller Area & System Design

Confirm chiller heat exchange area is sufficient and pipe configuration is reasonable. Add motorized valves on return lines to prevent backflow, and add air vent valves at end branches. Enlarge pipes or increase heat exchange area if necessary.

Cooling DifficultyReal Cases

2025.02.24LM-11F

Chengda Pharmaceutical · Jiashan

LM-11F replaced LM-1; reactor cooling performance poor

Comparison shows -50°C 11F viscosity (4) lower than Type 1 (10.28), but thermal conductivity is half; main cause of poor cooling

2025.05.28LM-8

- · Chongqing

LM-8 cannot cool below -42°C; plate heat exchanger localized icing

Recommended Type 1 (customer concerned about flash point); considering LM-11D but must ensure water-free system

2025.06.18LM-4

Wanwei Group · Anhui Chaohu

Glycol system severe corrosion; PV polymer material contamination

Need sampling to test enhancer effectiveness. New system recommends LM-4; enhancer addition plan has risks

2025.09.29LM-11C

Dachen Pharmaceutical · Taizhou

LM-11C reactor bulging and deformation

Valve closure with temperature change caused volume change and pressure. Do not close outlet valve; maintain tank connection

2025.10.24LM-8

- · Zhejiang

LM-8 cannot cool below -36°C (set point -50°C)

Insufficient system flow causing heat exchanger icing. Raise to above 0°C then reset to -45°C operation

2025.11.15LM-445

Chongqing Jinguan · -

LM-445 cannot cool below -16°C

Possible insufficient heat exchanger area or pump flow. Recommended setting -17°C and slowly cooling to find lower limit

2025.10.16LM-4

- · Zhejiang

System operating temperature difference too small (1-1.5°C)

Low end-load, high pump flow. Recommended reducing pump frequency to lower flow

Physical Property Comparison Essentials

When replacing coolant, you must compare the following key physical properties:
Viscosity: Affects pump resistance and flow rate. 7.5% viscosity increase corresponds to 7.5% resistance impact and ~1.5% heat exchange impact.
Thermal conductivity: Directly affects heat exchange capacity. LM-11F thermal conductivity is about half that of LM-1, the main cause of poor cooling.
Specific heat: Affects the cooling capacity of the coolant. LM-11D specific heat is lower than LM-4, resulting in less cooling at the same flow rate.
Freezing point: Should be 10-15C below minimum operating temperature. Too high a freezing point causes coolant to freeze at the evaporator.

CoolingFAQ

System temperature cannot reach design value (e.g., set -50°C but only reaches -36°C)

Cause: Possible causes: high coolant viscosity reducing flow, localized heat exchanger icing, undersized pump, excessive concentration, insufficient heat exchanger area

Solution: Troubleshooting: verify pump flow meets requirements; temporarily raise temperature to melt ice then slowly cool; check if concentration is too high (increases viscosity); compare thermal conductivity with previous medium

Reactor cooling performance deteriorates

Cause: Different thermal conductivity after coolant replacement reduces heat exchange. Viscosity differences affect flow

Solution: Compare thermal conductivity and viscosity of old and new coolants. Calculate viscosity impact on resistance and heat exchange (generally 7.5% viscosity increase = 7.5% resistance impact, 1.5% heat exchange impact), determine if within acceptable range

LM-8 cannot cool below -42°C

Cause: Plate heat exchanger localized icing, cooling capacity cannot transfer. Evaporation temperature too low causes heat exchange surface icing

Solution: Raise evaporation temperature or lower supply temperature setpoint. Consider replacing with LM-11D (water-free, no icing), but ensure system is water-free

Cooling difficulties and foaming after adding performance enhancer

Cause: Enhancer component precipitates and forms foam, affecting heat exchange efficiency

Solution: Remove foamy material from tank. May need defoamer addition. Stop system, circulate for 24 hours, then resume cooling and observe

Cold storage temperature cannot reach target

Cause: Improper concentration (too high increases viscosity and reduces flow), unreasonable system design (pipe configuration issues)

Solution: Check concentration; reducing concentration can improve flow. Check pipe configuration; add electric valve on return line to prevent backflow; add air vents at branch ends

Cooling Performance Troubleshooting