Danfoss Pressure Switch Buying Checklist: 6 Things I Check Before Ordering Another KP or RT Switch

If you've ever ordered a Danfoss pressure switch and found out at installation that the terminals are different from the one you pulled off, you know the exact feeling. It's not just the cost of the part. It's the service call, the downtime, and the second trip to the job site.

I'm a procurement manager at a 40-person refrigeration service company. I've managed our controls and components budget - about $180,000 a year - for six years, negotiated with more vendors than I want to count, and logged every order in our cost tracking system. I'm not an electrician, so I won't pretend to give you a substitute for a licensed sparky. What I can tell you is what to check before you order, before you wire, and before the tech goes back to the truck.

Quick scope note: if you came here for a BMW oil filter or an oil filter silencer adapter 9mm, this page won't help you. That's outside what I source and outside what this checklist covers. This is about industrial pressure switches.

When this checklist helps

Use this when you're replacing a failed pressure switch, building a panel, or ordering a spare for a critical chiller. It applies to Danfoss pressure switches in the KP, RT, MBC, and KPI families. I'll give you six steps. Step 3 and Step 5 are the ones most people skip.

1. Confirm the switch family and function

'Danfoss pressure switch' is not one orderable part. The KP series includes low-pressure, high-pressure, differential, and dual-pressure controls. A KP1 is not a drop-in replacement for a KP15. If your system needs a Danfoss dual pressure switch, you need to know both the low-pressure and high-pressure settings, or you're guessing.

Look at the old switch's full model code before you search. 'KP15' alone is a start, but there are variants with different ranges, reset modes, and connection sizes. Write down the entire code and the date code if you can read it.

2. Confirm the pressure range and differential

The right family can still be the wrong switch. A dual pressure switch like the KP15 has separate low-pressure and high-pressure scales. The cut-in and cut-out values have to match the refrigeration circuit, and the differential has to match the application. Ordering 'a KP15' without checking the range can cause short cycling or no start at all.

In my first year, I made the classic spec error: assumed the model number was enough. It wasn't. The switch we ordered looked identical, but the pressure range was wrong. That mistake cost us a $600 redo and an unhappy customer.

If the old switch has no tag or the label is worn, use your manifold gauges to record the actual cut-in and cut-out before you remove it. That gives you a working spec even without a readable part number.

3. Pull the right wiring diagram before you disconnect anything

If you type 'danfoss kp15 pressure switch wiring diagram' into a search engine, you'll get a pile of images. Some of them are for other variants, and a few are just wrong. Use the current Danfoss datasheet or the manual that came with the unit. The datasheet shows the terminal arrangement for both rising and falling pressure, and it lists whether the contact is normally open or normally closed at rest. As of January 2025, the KP15 datasheet on Danfoss's site still includes that diagram and the contact position tables.

Take a photo of the existing wiring before you remove the old switch. Label the wires. (I really should do this on every job; I've skipped it on rush calls and it always costs more time than it saves.) Then compare that photo to the datasheet diagram. Trust me on this one.

4. Power down and test with a voltage tester

If you're asking 'how does a voltage tester work,' here's what you need to know: a two-pole tester lights up or beeps when there is voltage between the probes. That's enough to confirm a circuit is dead before you work on it. Use a tester rated for the voltage, and test the terminals you're about to touch, not just the wire you think is the feed.

I've been on sites where someone turned off the wrong breaker, and the switch was still live from a separate circuit. That's not the time to learn the difference between a no-contact tester and a real two-pole tester. This is the one step I don't let schedule pressure squeeze out.

5. Compare total cost, not just the invoice price

The conventional wisdom in procurement is to get multiple quotes. Fine. But after tracking 200+ orders, I've learned that the lowest quote is only the starting point. The total cost includes delivery lead time, freight, the restocking fee if it's wrong, and the cost of downtime if it fails to arrive.

In Q2 2024, I compared six quotes for a Danfoss dual pressure switch. The cheapest supplier was $32 below our usual vendor. But their lead time was 10 days, and their phone support stopped at 5:00. Our chiller downtime costs about $180 per hour. A 10-day wait wasn't a $32 savings; it was a potential $4,000 problem.

Bottom line: the price on the purchase order isn't the cost. The cost includes what happens after the part is delivered.

That doesn't mean you always pay more. It means you evaluate the whole picture before you pick. And read the vendor's return policy before you order. If the restocking fee is 25%, an order mistake is a lot more expensive than the part difference.

6. Inspect small details before the tech goes to site

Most people check the pressure range, then stop. Check the rest before the part leaves your bench:

• Pressure connection: 1/4 NPT, 1/2 BSPP, flare, or capillary? They aren't interchangeable without an adapter.
• Reset mode: automatic or manual reset? A manual reset switch won't restart the system on its own, which can be exactly what a safety control should do.
• Contact type: normally open or normally closed at rest? The same KP15 can be set up differently depending on the contact sequence.
• Included hardware: gasket, mounting bracket, screws. Missing pieces turn into another order.
• Factory set vs adjustable: some switches are sealed; make sure your spec calls for the right one.

Also, if you're replacing an oil pressure switch and the compressor still trips afterward, don't order another switch first. Check the oil pressure and the oil filter. A new switch won't fix a plugged oil filter. That lesson came from one of our techs after a long day of diagnosing an 'intermittent fault.'

What still goes wrong

A few things I've seen more than once:

• Replacing the switch without fixing the root cause. A pressure switch that fails often fails because something else in the system changed.
• Using a generic wiring diagram instead of the variant-specific datasheet.
• Assuming the old part number is still the right part number. Danfoss has consolidated some KP variants over the years.
• Forgetting to check the capillary length on remote-bulb versions. The box may say the right model and still have the wrong tube length.
• Relying on Internet images for terminal identification, then wondering why the compressor won't start.

Final thought

A pressure switch is a small part, but a wrong one can stop a whole line. The twenty minutes you spend checking the model code, the wiring diagram, and the actual connection details will save you the two-hour redo. That's the kind of cost control I care about.