The Danfoss Pressure Switch Checklist I Use Before Every Order

Look, if you've typed Danfoss pressure switch into a search bar and ended up with a catalogue that lists 40 models, I understand. I've spent nine years handling industrial control orders and field installs. I've personally made and documented 11 significant mistakes, totaling roughly $18,000 in wasted budget. One of my worst was ordering a Danfoss dual pressure switch with the wrong reset function. That error cost $890 in restocking fees and a week of downtime. Now I maintain our team's checklist so the next person doesn't repeat it.

This checklist is for refrigeration technicians, HVAC engineers, and plant operators who need to select, wire, and test a pressure switch without guessing. It's not a replacement for the official manual. It's the list I wish someone had given me before my first wrong order.

1. Start with the function, not the model

It took me about six years and a lot of swap-outs to understand that the model family matters less than the function you're asking the switch to perform.

Before you open the Danfoss differential pressure switch catalogue, answer this: what is the switch actually controlling?

• Low pressure control: usually manages a minimum or suction-side pressure, often in refrigeration pump-down circuits.
• High pressure cut-out: protects the discharge side from exceeding a limit.
• Danfoss dual pressure switch: combines low and high pressure functions in one device. A common example is the KP35.
• Differential pressure switch: measures the difference between two pressure ports, which is how it can detect a clogged filter or a blocked airflow path.

Why does this matter? Because a dual pressure switch and a differential pressure switch are not interchangeable. I'd rather spend 10 minutes explaining the difference than watch you order the wrong switch twice.

2. Match the series to the duty

Danfoss makes several pressure switch families. The KP series is compact and common on refrigeration racks and small compressors. The RT series is larger, heavier, and used in industrial applications. The MBC series is built for compressors and pumps, with more robust housings and connection options.

Don't pick a series because it sounds industrial. Pick it because the ratings match your system and your environment.

I can only speak to refrigeration and air compressor duty. If you're dealing with a classified area, aggressive chemicals, or extreme vibration, you need to verify approvals and wetted materials yourself. Your mileage may vary.

3. Check range and differential, not just the model number

A pressure switch is defined by two numbers: the set-point range and the differential (i.e., how far the pressure has to change before the switch resets). The range tells you where the switch can be adjusted. The differential tells you whether the switch will behave correctly in your system.

If you choose a switch with the right range but the wrong differential, you'll get nuisance trips or a system that never stops. The official Danfoss datasheets list these values separately. Use them.

The reset function is not a footnote. On a high-pressure cut-out, manual reset can mean the difference between a controlled shutdown and a compressor that cycles itself to death.

Here's the step most people ignore: check the reset function, especially on a dual pressure switch. Some dual pressure switches have automatic reset on the high-pressure side. Others need a manual reset. If you're protecting a compressor, the manual reset version can prevent short-cycling after a high-pressure trip. I still kick myself for ordering the auto-reset version when I needed manual. If I'd spent two minutes on the datasheet, we'd have saved the restocking fee and a six-day wait.

4. Verify contacts and switching capacity

The pressure switch often doesn't switch the motor directly; it switches the coil of a contactor or an alarm input. Check the contact rating. If you're working with a PLC, you may need gold contacts for low-voltage, low-current circuits. A switch rated 16 A at 250 V is not automatically suitable for a 4–20 mA input or a 5 V PLC signal.

Do not assume a switch that works on a clean control panel will survive outdoors or in a washdown area either. The IP rating is part of the specification.

5. Check the pressure connection before you order

This sounds basic, but I've seen it fail a dozen times. The pressure port has a thread type: G 1/4, 1/4 NPT, flare, or something else. The catalogue lists this spec, but it's easy to skip when you're in a hurry.

So glad I checked the port size once before finishing an RT series order. Almost had to expedite an adapter for a shutdown job.

6. Read the wiring diagram before you touch a terminal

Danfoss pressure switches have numbered terminals. The wiring diagram is usually in the installation guide PDF, and sometimes printed on the side of the switch. Use it.

I once wired a dual pressure switch with the low-pressure and high-pressure terminals reversed. The compressor wouldn't start, and the electrician blamed the switch. The switch was fine; the wiring logic was wrong. That was a stupid way to lose half a day.

7. Test it in the field, with a reference you trust

Set the switch using a calibrated gauge or a known test pressure, not the readout on an old manifold. Then cycle the system. Does the switch make or break at the correct pressure? Does it reset when pressure rises or drops? Does the dual pressure switch perform both functions independently?

Do this test while you're still on site. It's much cheaper to fix a setting there than to come back after the system has been running for a day.

If you're using a differential pressure switch, test the difference between the two ports. A single pressure reading won't tell you anything.

What I'd tell myself before the first order

• Dual vs differential: A dual pressure switch is not a differential pressure switch. One combines low and high functions; the other measures a pressure difference.
• Reset type matters: If the system can short-cycle on a high-pressure trip, manual reset is not a nice-to-have. It's a decision.
• Contacts are part of the spec: Low-voltage PLC signals need the right contact material.
• Thread type is a spec: "I'll make it work" usually means a trip to the supplier.
• Test before leaving: A setting that looks right on paper is not the same as a proven setting.

That's the checklist. The next time someone asks me to find a Danfoss pressure switch, I start with the function, check the reset, and test the switch in the actual system. It's a lot cheaper than my tuition.