Condensation inside electrical enclosures during the rainy season—when humidity is high—**can definitely interfere with vacuum sensors. These malfunctions fall into two categories: “soft” faults, such as signal drift or spiking; and “hard” faults, such as insulation breakdown leading to alarms or even sensor damage**. The interference pathways can be divided into two parts: the pressure-sensing side of the sensor itself and the electrical signal side. During on-site troubleshooting, many technicians focus solely on leaks in the vacuum lines while overlooking condensation in the electrical enclosure as the root cause.

Most vacuum sensors consist of a pressure sensing element and a transmitter circuit board. If the circuit board is housed inside the electrical enclosure of an outdoor unit, the significant day-night temperature fluctuations during the rainy season can cause the air inside the enclosure to reach saturation. When the enclosure temperature drops, moisture condenses into a water film on the surface of the circuit board, the pin terminals, and the terminal blocks. This film of water reduces the surface insulation resistance of the circuit board, causing leakage in the signal circuit. As a result, the 4–20 mA analog signal shifts, leading to a slow drift in the vacuum reading and fluctuating values that swing between high and low. With minor condensation, the readings fluctuate erratically but the unit can continue to operate; however, the vacuum control logic adjusts back and forth based on the erroneous readings, causing the vacuum pump to start and stop frequently and resulting in persistently unstable evaporation conditions. As condensation worsens, micro-short circuits form between terminals, causing the signal to jump to the maximum or drop to the minimum, triggering a vacuum fault alarm. Maintenance personnel inspect the vacuum lines, gaskets, and condenser but cannot locate a leak; once the circuit board is wiped dry, the readings immediately return to normal.

There is another hidden path for condensation—not on the circuit board, but in the pressure-sensing tubing of the sensor. This tubing runs from the negative-pressure zone of the evaporator chamber to the pressure sensor element inside the electrical enclosure. Under negative pressure, a small amount of water vapor travels through the tubing into the sensor chamber. During the rainy season, when temperatures inside the enclosure are low, the water vapor condenses into droplets on the metal diaphragm inside the pressure sensor element. These droplets adhere to the surface of the pressure-sensing diaphragm, effectively imposing an additional static pressure on the diaphragm. This directly alters the pressure measurement reference, causing the vacuum reading to remain persistently high—that is, the displayed vacuum appears better than the actual operating conditions. This results in the paradoxical situation where the instrument indicates that the vacuum meets the standard, yet the actual evaporation rate continues to decline. If too many water droplets accumulate inside the pressure-conducting tube, a liquid seal may form, blocking the transmission of negative pressure. As a result, the vacuum reading will freeze and no longer track the actual pressure changes in the chamber.

The secondary issues caused by condensation must not be overlooked either. A moist water film accelerates the oxidation and corrosion of copper foil on circuit boards and terminal blocks, producing conductive verdigris. These corrosion byproducts continuously cause signal instability; even if the condensation temporarily evaporates, the corrosion residues will still lead to intermittent failures. Long-term condensation will also gradually erode the sensor’s internal sealing structure, allowing moisture to penetrate the sensor core and ultimately causing permanent sensor failure. Furthermore, condensation inside the electrical cabinet is rarely isolated to a single point; PLC modules and relay terminals within the cabinet are often affected simultaneously, leading to valve malfunctions that indirectly amplify disturbances in the vacuum system.

It is easy to distinguish between vacuum failures caused by condensation and those caused by pipeline leaks on-site. Vacuum abnormalities triggered by condensation mostly occur during the early morning or on overcast, rainy days when temperatures drop; during the day, as the sun warms the cabinet and dries it out, the symptoms subside or even disappear; When a failure occurs, the vacuum reading fluctuates without a consistent rate of decline; rather than a continuous, gradual drop in vacuum, the reading drifts or jumps erratically. After ventilating and drying the electrical cabinet and purging the sensor terminals, the reading quickly recovers, and a pressure-holding test confirms the vacuum piping is airtight. In contrast, a pipeline leak causes the vacuum to decline continuously regardless of the time of day or weather conditions, and a pressure-holding test can pinpoint the leak location.

Corresponding preventive measures: Electrical enclosures should not be simply sealed shut, as fully enclosed enclosures are more prone to internal condensation due to diurnal temperature fluctuations. Prioritize the installation of temperature-controlled dehumidification devices or enclosures equipped with drain-and-vent valves to maintain the internal dew point below the ambient temperature; Vacuum sensors should be moved out of the main electrical cabinet whenever possible and installed as close as possible to the negative pressure piping to minimize the length of the pressure-transmitting tubing. Condensate drain ports should be added to the tubing to periodically drain accumulated water; use waterproof connectors with sealing gaskets at the wiring terminals to reduce the ingress of moist air into the cabinet; at the program level, add vacuum signal filtering to filter out transient spikes and prevent a single abnormal signal from directly triggering an interlock shutdown.