Complete Logic: Aging of the Inverter-Controlled Air-Cooled Fan, Insufficient Cooling → Poor Condensation → Continuous Drop in Evaporator Vacuum

I. Core Chain of Events

Insufficient fan cooling → Decreased heat exchange efficiency of the condenser → Inability to fully liquefy secondary vapor → Accumulation of large amounts of non-condensable vapor in the gas phase → Rise in overall system absolute pressure → Continuous deterioration of apparent vacuum

1. Insufficient cooling capacity on the condenser side, resulting in elevated saturated pressure

In heat pump systems with low-temperature evaporation, the condenser relies on air cooling to remove the latent heat of secondary vapor. When the fan’s inverter ages, its speed cannot be increased, and airflow decreases, leading to poor fin heat dissipation. Consequently, the refrigerant and cooling water temperatures in the condenser remain persistently high.

The condensation temperature of vapor corresponds to a fixed saturated pressure; the higher the cooling medium temperature, the more difficult it is to liquefy the vapor. The volume of uncondensed vapor in the chamber continues to increase, the pressure in the vapor space steadily rises, and the vacuum reading drops.

2. Large amounts of uncondensed vapor occupy the vapor space, saturating the vacuum pump’s pumping capacity

Vacuum pumps can only remove gas; they cannot directly liquefy vapor.

Once heat dissipation fails, a continuous stream of uncondensed steam floods the vacuum lines and buffer tanks. The vacuum pump’s suction capacity reaches its limit, unable to expel the gas from the system in time. Consequently, the pressure inside the chamber cannot be reduced, and the vacuum remains persistently low; even if the vacuum pump operates at full capacity, it cannot offset the continuously increasing volume of gaseous steam.

3. A vicious cycle forms within the system, causing the vacuum to deteriorate further

Vacuum drops → Material boiling point rises → Increased steam production at the same heating power;

As steam production increases, the condenser side becomes further overloaded, amplifying the heat dissipation bottleneck;

More steam cannot be condensed, pressure continues to rise, and vacuum continues to drop, creating a vicious cycle of deterioration.

4. High-pressure interlock interference in the refrigerant system (specific to heat pump models)

Air-cooled fans are responsible for cooling the heat pump’s refrigerant condenser:

Poor heat dissipation causes the refrigerant high-pressure to rise, triggering the unit’s high-pressure protection mechanism, which automatically reduces the compressor’s heating output;

Insufficient heating temperature leads to unstable vapor production during evaporation, causing intermittent surges of steam to impact the condenser, resulting in frequent vacuum fluctuations and a continuous decline in the overall average vacuum level.

5. Inability to Effectively Separate and Evacuate Trace Non-condensable Gases

Under normal operating conditions, most vapor is liquefied, and small amounts of air and volatile non-condensable gases are easily evacuated by the vacuum pump;

When heat dissipation is insufficient, the entire piping system becomes filled with large amounts of water vapor. The partial pressure of water vapor dominates, diluting the non-condensable gases, and the vacuum pump’s efficiency in removing non-condensable gases drops significantly. Air remains trapped in the chamber for extended periods, contributing to increased pressure and persistently low vacuum levels.

II. Verification through Observable Associated Symptoms

The current of the air-cooled fan is abnormally low, and the fan speed cannot reach full capacity; the fins remain at high temperatures and are too hot to touch;

The temperature difference between the condenser inlet and outlet has significantly narrowed, and the condensate discharge volume has noticeably decreased;

The vacuum pump operates at full load and high frequency for extended periods; although the current is high, the vacuum level still fails to rise;

The temperature of the evaporation chamber is correspondingly high, resulting in reduced concentration efficiency and increased energy consumption.