Danfoss Pressure Switch: How to Pick the Right One When Time Is Not on Your Side

Here's the answer up front. Match the Danfoss pressure switch series to your application: KP for standard refrigeration and HVAC, RT for industrial and washdown environments, MBC for compact OEM builds, the MP 55 when you need differential pressure monitoring, and the KPI series for compressor oil pressure protection. Once you've got the series right, the rest is just setting range and connection size.

I'm not guessing. I've spent 15 years sourcing and installing industrial pressure switches, with most of my work handling emergency replacements. When a client calls at 2 PM with a compressor offline and 32 pallets of dairy product at risk, you don't have the luxury of a two-week research project. You need to know, in minutes, which switch goes where. That's what this field guide is for.

Why I'm Confident About This

Last year alone, I processed 47 rush orders for pressure switches, with 95% delivered on time. That number isn't about being lucky. It's about having a selection framework that's been tested against real failures.

In March 2024, a cold storage facility called on a Friday afternoon. Their RT 116 high-pressure switch had failed, and if the refrigeration system didn't come back online by Saturday morning, the entire inventory was going to spoil. The pressure range was the easy part—8 to 32 bar, standard for that duty. The real question was understanding why the original switch was an RT rather than a KP. The answer? The IP66 rating. The unit was installed in an area that gets hosed down weekly. An IP44 KP switch wouldn't have lasted two years in that environment. That one detail meant the difference between an overnight fix and a roughly $50,000 write-off.

The Series Breakdown (The Part You Actually Came For)

Let me walk through this the same way I do when I'm triaging an order.

KP Series: The Default

If you maintain refrigeration racks, HVAC units, or packaging machinery, the KP series is your most likely replacement. It's the broadest line in the Danfoss pressure switch portfolio.

The KP 1 is a low-pressure switch, usually for pump-down control. The KP 15 combines low and high pressure in a single unit—two protection points, one switch. The KP 35 handles high-pressure cut-out, with ranges up to 32 bar. And if you need manual reset for a safety application, the KP 36 is the version you'd pick. These are decent workhorse switches, but they're rated IP44. Indoors or in a protected enclosure, they're perfect. Damp environments? Not so much. Don't skip that detail.

RT Series: When the Environment Bites Back

The RT series is the heavy-duty option. IP66 housings, better resistance to vibration, wider temperature tolerance, and a more robust switching mechanism. The RT 116 is the high-pressure switch I source most often for industrial refrigeration. The RT 118 does the same job for low-pressure control.

Here's the simple way to think about it: if the switch is exposed, use RT.

MBC Series: The Compact One

MBC switches are smaller and designed for OEM and tight-fit installations. The MBC 5100 is a common pick when you need a reliable high-pressure switch in a control cabinet that doesn't have an inch to spare. It's a snap-action switch, which means you get a positive break and make without slow contact wear.

MP 55: The Differential Pressure Option

Now, if your search was for a Danfoss differential pressure switch, the MP 55 is the model to focus on. It doesn't measure against atmospheric pressure. Instead, it compares two pressure inputs and trips when the difference between them reaches your set point.

Classic use case? Filter monitoring. As a filter loads up, the pressure drop across it increases. The MP 55 catches that and gives you a signal to clean or replace the filter before it becomes a problem. It's also used for flow detection in some systems. Not the most technically dramatic switch in the catalog, but genuinely useful.

KPI Series: Oil Pressure Protection

If you landed here because you searched for a Danfoss oil pressure switch, the KPI series is what you need. These are oil differential pressure switches that protect compressors from losing lubrication. They measure the difference between oil pump pressure and crankcase pressure. If lubrication drops dangerously low, the switch cuts the compressor before the bearings decide they've had enough.

One quirk: KPI switches include a built-in time delay. That delay exists so a temporary oil pressure dip during startup doesn't trigger a nuisance trip. If a compressor shuts down right after starting, the switch isn't the problem. The problem is that oil pressure never came up in the first place.

Installation: Where Good Plans Go Bad

Selecting the right series is half the job. The other half is getting it installed without causing a second failure.

Wiring: Trust the Diagram, Not Your Memory

KP series switches use standard terminal markings: 1 for common, 2 for normally closed, 4 for normally open. If you've installed a few, you've memorized that.

And that's exactly the trap.

A couple of years ago, I was swapping out a KP 35 on a rooftop HVAC unit. Installing a pressure switch is routine. I didn't read the wiring diagram on the new switch because I "knew" the layout from dozens of previous installs. Well, that production run used a slightly different terminal arrangement. The compressor short-cycled three times before I stopped, pulled the cover off, and actually read the label. No equipment damage, but it cost us an hour and some client confidence. Learn from my laziness: photograph the old wiring before disconnecting, and check the diagram on the new switch. It's a two-minute habit that prevents a miserable afternoon.

Setting Ranges: The Scale Is Not a Calibration Tool

Every Danfoss pressure switch has a range scale on its adjuster. It's a reference, not a certified calibration. If your set point matters—and it always does—verify it with a pressure gauge or calibrator.

The nastier one is the differential adjustment. On KP switches, the differential controls how far below the set point the switch resets. Too tight, and you get rapid short-cycling. Too wide, and the system may not restart when pressure recovers. The first time you chase a problem caused by that, you'll remember this paragraph.

Check the Nameplate

If you're replacing a switch, the old unit's nameplate is your friend. Every Danfoss switch has a model stamp, a range marking, and an electrical rating printed on it. I've taken calls from panicked maintenance managers who were convinced they had an unusual model, only to read them the model number right off the photo they sent. The nameplate answers most questions before you even open the datasheet.

When This Framework Doesn't Apply

I don't want you to treat this like a universal law, because it isn't. A few honest caveats.

My experience is concentrated in HVAC, refrigeration, and light-to-medium industrial applications. If you're in oil and gas with hazardous area classification, you're not choosing by series alone—you're choosing by ATEX certification and project documentation. Danfoss makes ATEX-rated versions of several KP switches, but that's a different selection process driven by compliance, not convenience.

This framework also assumes you're replacing a switch on an existing system. If you're designing a new system from scratch, you should be thinking about the full control loop and the entire protection strategy, not just which pressure switch to bolt on.

And one final note: I can only speak to genuine Danfoss units sourced through normal distribution channels. If you're looking at a switch with a missing nameplate or getting parts from an unfamiliar supplier, the wiring and range information I've given you might not apply. A part number that looks similar but isn't identical can behave in a very different way. Verify the model stamp.

Here's the right way to read this article: if you're an engineer or technician staring at a failed pressure switch and a deadline, this framework gets you from "what do I order" to "it's ordered and arriving tomorrow" in about 5 minutes. That's the entire goal. Selecting a Danfoss pressure switch doesn't require a week of catalog deep-dives—it requires knowing your application, matching the series to it, and then trusting the nameplate.