Why Our HVAC Equipment Kept Failing — And How DR3602 Fixed It

Introduction

It tripped at 70 bar last month. 85 bar this month. Our commercial HVAC chiller loop was experiencing erratic pressure spikes, leading to repeated compressor lockouts and a staggering $12,500 in emergency repair costs over a single quarter. As system integrators, we realized our existing single-point control logic was fundamentally inadequate for these dynamic load conditions. We needed a reliable dual setpoint pressure switch to properly manage these fluctuations and protect our critical infrastructure.

The Problem: One Pressure Point Wasn’t Enough

The core issue stemmed from the physical limitations of our legacy control hardware. Single-relay switches can’t provide both high and low alarm protection simultaneously within the same fluid circuit. Consequently, when the system pressure dropped too low due to a minor leak, the single relay could not trigger a low-pressure warning while still guarding against the high-pressure spikes exceeding 90 bar in our 0-100 bar operating range. We attempted to wire two separate mechanical switches in parallel; however, this traditional method failed due to calibration drift and conflicting deadbands, leaving our pump control logic highly vulnerable.

The Solution: DR3602 Dual Relay Pressure Switch

To resolve this control gap, we integrated the DR3602 Dual Relay Pressure Switch into our primary HVAC manifold. This specialized dual relay pressure switch features two independent relays for high/low alarm or pump control, allowing us to establish precise operational boundaries within a single device. By utilizing its programmable setpoints and hysteresis, we configured the first relay to maintain standard pump operation and the second relay to trigger a hard shutdown if pressures approached critical limits. Therefore, this high low alarm pressure switch provided the exact dual-state control we required, easily monitored via its integrated 4-digit LED display.

Results

Since installing the DR3602, our facility has recorded a 100% reduction in nuisance trips and compressor lockouts. The precise pump control pressure switch logic allowed us to stabilize the chiller loop, completely eliminating the $12,500 quarterly maintenance drain. As a result, the system achieved full return on investment within the first 45 days of operation, proving the long-term financial viability of upgrading to solid-state dual-relay instrumentation.

Why Dual-Relay Control Matters in HVAC Systems

HVAC pressure control is rarely just about detecting whether pressure is “normal.”

Different pressure conditions can require different actions.

A low-pressure condition may require the pump to start or an alarm to be activated. A high-pressure condition may require the compressor or pump to stop immediately.

A high low pressure switch with independent relay outputs makes it possible to assign these functions separately.

This is particularly useful for:

• Dual independent relays for high/low alarm
• Programmable setpoints and hysteresis
• 4-digit LED display
• 4-20mA analog output optional
• RS485 output optional
• 24VDC powered
• NEMA 4X / IP65 enclosure

Conclusion

Relying on outdated single-point switches for complex HVAC systems inevitably leads to equipment failure and costly downtime. By implementing a dedicated dual relay pressure switch, integrators can secure comprehensive high and low-pressure protection in one robust package. Are you still trusting your critical pump control systems to inadequate legacy hardware?

Tags: #pressureswitchwithdelaytimer #adjustablehysteresis #NEMA4Xpressureswitch #DR3602