Danfoss Pressure Switch FAQ: Straight Answers When You're Under the Clock

I'm a field controls specialist, and I've spent the better part of a decade on the service side of industrial refrigeration and HVAC. That means I've handled my share of pressure switch problems, including the kind that show up at 4:30 PM on a Friday. Danfoss pressure switches are everywhere: compressor racks, chillers, air-handling units, hydraulic skids. When a plant calls with one down, the questions are almost always the same.

Here's the FAQ I tend to work through, answered the way I would on an actual service call.

• Which Danfoss pressure switch do I actually need?
• Where do I find Danfoss pressure switch distributors in a hurry?
• Where can I find the Danfoss oil pressure switch manual?
• How do I set the cut-out and differential on a Danfoss pressure switch?
• Why is my new Danfoss pressure switch chattering or tripping right away?
• Can I substitute another Danfoss pressure switch model if the original isn't available?
• What should I do today so I don't need a rushed order later?

Which Danfoss pressure switch do I actually need?

When I'm triaging a rush replacement, the first thing I ask for isn't a series name. It's the code number from the silver rating plate. KP, RT, and MBC only tell you which product family you're looking at:

• KP series: compact pressure switches, mostly found in refrigeration, air conditioning, and compressor applications. Models like KP1, KP15, KP35, and KP36 are common, and each one has its own pressure range, differential, and reset behavior.
• RT series: the heavier industrial and marine line, usually with a metal enclosure. An RT116 still shows up in plenty of older panels.
• MBC series: compact modular switches aimed at OEM and industrial applications, such as the MBC 5100.

The exact model number does the real work. Over the past twelve months alone, I've helped chase down replacements for more than forty different Danfoss pressure switch codes. Every one that went smoothly started with the code from the rating plate. A Danfoss order code, often printed as 017-xxxx below the type designation, is what a distributor needs to pull the right switch from the shelf. If the rating plate's scratched off or missing, you're guessing, and guessing usually costs you a second trip.

Where do I find Danfoss pressure switch distributors in a hurry?

Danfoss generally sells through authorized industrial distributors rather than direct to end users. If the clock's running, the distributor locator at danfoss.com is the official starting point. As of January 2025, that still beats scrolling through generic parts aggregator sites for a brand-specific component.

Call with the full type designation and code number in hand. A good distributor can check stock in minutes. If someone tries to sell you a similar Danfoss pressure switch without asking for the code number, treat that as a warning sign, not a convenience.

One caution about marketplace listings: I've seen plenty of too-good-to-be-true Danfoss pressure switches online. To be fair, some of those sellers are authorized and perfectly legitimate. But gray-market and counterfeit switches do turn up. For a component that can shut a plant down, or fail to shut it down when it should, an authorized-channel invoice is worth the extra phone call.

Where can I find the Danfoss oil pressure switch manual?

If you type danfoss oil pressure switch manual into a search engine, you'll get a long list of PDFs, and most of them won't match your exact switch. Start with the code number from the rating plate, then look for the matching literature on the Danfoss product pages or documentation center.

The manual matters even more when the switch is protecting compressor lubrication. That application uses an oil pressure differential switch, not an ordinary single-pressure control. It compares oil pump pressure against crankcase or suction pressure, and the safety circuit needs a time delay so the compressor can build oil pressure during start-up. Danfoss MP 54 and MP 55 oil pressure switches are classic examples of this type. If someone replaces that assembly with a standard LP or HP switch, or bypasses the time delay, the compressor can trip on every start.

The manual gives you the wiring diagram, terminal numbering, and the recommended setting procedure. Download the matching PDF before you take the old switch apart. That five-minute step has saved me more than one late-night redo.

How do I set the cut-out and differential on a Danfoss pressure switch?

Most mechanical Danfoss pressure switches have two adjustments: the main range and the differential. The main range sets where the switch changes state, and the differential sets the gap between cut-out and cut-in. If a high-pressure switch cuts out at X, for example, the pressure has to drop below X minus the differential before the switch resets.

Too narrow a differential causes short-cycling or chattering. Too wide a differential means the system runs well outside its normal window before the switch comes back. The two adjustments also interact, and the relationship isn't identical on every model. The scale printed on the switch housing is a reference, not a calibration-grade instrument. Set it close, then verify the actual cut-in and cut-out with a calibrated pressure gauge.

And don't ignore the reset mode. A manual-reset switch stays locked out until someone presses the button. An automatic-reset switch closes by itself when pressure returns. On high-pressure safety cut-outs, that difference is a safety feature, not a convenience option.

Why is my new Danfoss pressure switch chattering or tripping right away?

Before you call the switch defective, ask what the switch is actually seeing. Chattering usually means the pressure at the connection is oscillating around the setpoint. It can also mean the switch is mounted somewhere with severe vibration, which causes contact bounce regardless of the pressure.

People assume the chattering switch is causing the problem. More often, it's the other way around. The pressure is fluctuating, and the switch is the only component reporting it. I'm honestly not sure why bad switch is the default diagnosis. My best guess is that because the part's new, the rest of the system gets treated as innocent. It's usually not.

If the switch trips immediately every time the unit starts, compare the setpoint with the actual start-up pressure. A switch set below an unavoidable start-up spike will trip every time, even though it's doing exactly what you asked it to do.

Can I substitute another Danfoss pressure switch model if the original isn't available?

Sometimes, but only if you compare more than the pressure range. In my first year in the field, I made the classic rookie mistake: I matched the range and ignored the reset mode. I installed an automatic-reset switch where a manual-reset high-pressure cut-out had been. It cost us an evening callback when the compressor kept restarting itself and re-tripping instead of staying locked out until someone fixed the underlying cause.

Besides reset mode, check the differential range, contact arrangement, electrical rating, connection size, enclosure rating, and any approval markings. Cross-reference those against the original switch's datasheet. If the application is safety-related, I order the exact original code rather than trusting a cross-reference, even when the cross-reference looks right.

What should I do today so I don't need a rushed Danfoss pressure switch order later?

Walk the plant and photograph the rating plate of every critical pressure switch. That includes KP and RT switches already in service as well as MBC units in new machinery. Store the photos where the maintenance team can find them, and write the order code into your asset records.

Then buy one exact spare for each critical application and keep the associated manual PDF with it. Spare switches cost a lot less than an unplanned shutdown. And if you take those photos now, you won't be the person calling a distributor on a Friday afternoon trying to read a half-scratched code off a greasy rating plate.

The five minutes it takes to check those rating plates is the cheapest insurance I know.