Danfoss Pressure Switch FAQ: Installation, Testing & Emergency Tips

Danfoss Pressure Switch FAQ: What I've Learned from Hundreds of Rush Orders

I'm a maintenance planner at a mid-size refrigeration contractor. In my role coordinating emergency repairs for supermarkets and cold storage facilities, I've handled probably 300+ pressure switch replacements over the last six years. Sometimes that's a planned swap, more often it's a 3 PM call that a freezer case is down and the store manager is losing product. I've made plenty of mistakes along the way, so I'll share what actually works — and what doesn't.

Here are the questions I get asked most often, plus a couple you might not have thought to ask.

1. What is a Danfoss dual pressure switch and when would I use one?

A dual pressure switch combines a low-pressure and high-pressure cut-out in a single housing. You'll see them on refrigeration systems where you need to protect the compressor from both low suction (loss of charge) and high discharge (overpressure or blocked condenser). The Danfoss KP series, for example, has models like KP15 that are dual-function. In my first year, I made the classic spec error: I ordered two single switches when one dual would've saved wiring time and panel space. Cost me an extra hour of labor and a bit of pride. Now I always check the system requirements first.

2. How do I find the Danfoss pressure switch catalogue PDF?

Danfoss publishes detailed product catalogues on their website. Search for “Danfoss KP RT MBC pressure switch catalogue” and you'll find the official PDFs — they're about 80 pages covering all series, dimensions, wiring diagrams, and setting ranges. I keep a copy on my phone for field reference. Pro tip: the catalogue includes cross-reference tables for older models. Saved me twice last quarter when I needed to replace a discontinued RT116 with a modern equivalent.

3. Can I use a multimeter to test a Danfoss pressure switch?

Absolutely — and it's the quickest way to diagnose a switch that isn't switching. I've tested probably 200+ switches with a multimeter. Here's the routine:

• Disconnect power and remove wires from the switch terminals.
• Set your meter to continuity (or ohms).
• Connect probes to the common (C) and normally open (NO) terminals — should be open circuit when no pressure is applied.
• Apply pressure manually (or use a hand pump) until you hear the click. The meter should show continuity at the set point.

If it doesn't click at the expected pressure, the switch is likely damaged or the diaphragm is leaking. I'm mixing up the exact pressure values here — a KP1 might trip at 1 bar or 1.5 bar depending on the adjustment. Point is, the multimeter test is reliable. Just don't forget to recalibrate after adjustments.

4. Why is my Danfoss pressure switch not switching?

Three most common reasons I've run into:

1. Blocked impulse line — dirt, oil, or ice in the connection tube. I lost a whole afternoon on a freezer case because a tiny piece of copper deburr plugged the line.
2. Worn contacts — after thousands of cycles, the internal contacts can burn or pit. You'll hear the click but no electrical continuity. A multimeter test confirms it.
3. Wrong differential setting — the difference between cut-in and cut-out points is too narrow. On an RT series switch I had set the differential too tight; it kept cycling rapidly until the contacts welded shut. That was an expensive lesson — new switch plus a service call.

The most frustrating part: you'd think a simple switch would be foolproof, but field conditions always find new ways to surprise you.

5. How do I wire a Danfoss KP pressure switch?

The KP series typically has three terminals: common (C), normally open (NO), and normally closed (NC). For a typical compressor cut-out circuit, you usually connect the control voltage to C and NO. If you need fail-safe that cuts power on pressure rise, use NC. I've seen plenty of beginners wire the switch backwards — the compressor runs fine but the safety doesn't work. Check the diagram on the switch housing; it's laser-etched and easy to read. 'Put another way: always confirm whether your application needs the switch to open on rising pressure (cut-out) or close on rising pressure (cut-in).'

6. What's the difference between KP, RT, and MBC series?

Quick breakdown from what I use daily:

• KP series — compact, general-purpose, adjustable range typically up to 30 bar. Good for package units and smaller refrigeration.
• RT series — more robust, higher pressure capability (up to 60 bar), often used in industrial ammonia systems. The RT116 is a classic for high-pressure cut-out.
• MBC series — designed for OEM applications like food trucks and medical coolers, with fixed settings and no adjustment knob to prevent tampering.

If I'm in a rush, I check spare parts inventory: KP are usually stocked everywhere; RT might need a day or two. MBC are special order only unless you carry them, which most distributors don't.

7. How to adjust the set point on a Danfoss pressure switch?

Adjusting a Danfoss pressure switch is straightforward but easy to screw up:

1. Remove the cap (usually a Phillips screw or a thumb-turn).
2. Turn the large central screw clockwise to increase the cut-out pressure, counter-clockwise to decrease. Each full turn changes the setting by roughly 0.5 bar on most KP models — but I'm going off memory, you should check the specific model's data sheet.
3. The smaller screw adjusts the differential (difference between cut-in and cut-out). Turning it clockwise widens the differential.

I made the rookie mistake of adjusting the differential when I meant to adjust the cut-out. That caused the switch to short-cycle for a whole day until I realised what I'd done. Now I always mark the original setting with a sharpie before I start.

8. Where can I get an emergency replacement if mine fails?

If you need a Danfoss pressure switch same-day or next-day, here's what I've found works:

• Call your local refrigeration wholesaler — many carry common KP models on the shelf.
• If they don't stock, ask if they have a universal replacement (like the Johnson Controls P70) that can be configured to match Danfoss settings. Not ideal, but keeps the system running.
• Online distributors like Grainger or SupplyHouse sometimes offer overnight shipping on Danfoss parts.

I had a situation last March: 36 hours before a supermarket's health inspection, their walk-in cooler's high-pressure switch failed. Normal lead time was 3 days. We found a local supply house that had a KP35 in stock, paid $22 in rush shipping to get it there by 7 AM, and installed it in 45 minutes. The alternative was losing product worth probably $8,000 — and failing inspection. That's when I started keeping a spare KP15 in my truck.

One more thing: I have mixed feelings about buying pressure switches online without seeing the physical product. On one hand, prices are lower. On the other, I've received switches that were old stock with corroded terminals. I compromise: I buy from a reputable distributor with a return policy, and I always bench-test before installing.