Three Situations, One Switch: How to Choose the Right Danfoss Pressure Switch When the Clock Is Ticking

There isn't one "best" Danfoss pressure switch—here's what actually matters

If you Google “Danfoss pressure switch” hoping for a single recommendation, you’re going to be disappointed. Because the right answer depends entirely on your situation: are you engineering a new system from scratch? Replacing a unit that just failed on a Friday afternoon? Stocking a spare for a customer who needs it tomorrow?

I learned this the hard way. When I first started specifying pressure switches, I thought a KP35 would fit most light-industrial jobs. Then a refrigeration integrator called at 4 PM needing an MBC 5100 for a glycol loop—and I had none in stock. That mistake cost us a same-day courier and a lot of goodwill. So let's break this down by scenario, so you don't make the same guess.

Here are the three most common situations I see in the field, and the Danfoss switch that fits each.

Scenario A: You're Engineering a New System (No Existing Switch)

This is the cleanest scenario. You're designing an HVAC or refrigeration line, and you can pick any Danfoss pressure switch that meets your specs. The focus here is on accuracy and range, not speed.

My recommendation: The RT series, specifically the RT 116 for differential pressure.

The RT line is Danfoss's heavy-duty mechanical switch. It’s been around for decades, and the documentation is thorough—wiring diagrams, pressure range tables, everything you need for a clean installation. The RT 116, for example, handles differential pressure from 0 to 11 bar, with a fixed hysteresis. It's not the cheapest, but the reliability is well-documented. (Source: Danfoss RT series datasheet, 2024 edition.)

In my role coordinating controls for industrial refrigeration projects, I've specified RT switches for ammonia and CO2 systems. The repeatability is excellent—I've seen them hold setpoint within ±1% over 18 months. That's the kind of data you want when you're designing a warranty-backed product.

One thing I wish I knew earlier: pay attention to the electrical rating. The RT series comes with different microswitches. If you're switching a 10A load at 250VAC, the standard version works. But for high-inrush loads (like motor starters), you might need a Gold Flash contact version. It's a small detail that saves a lot of callbacks.

Scenario B: You're Replacing a Failed Switch—and It's Urgent

This is where things get stressful. A machine is down. Production is waiting. The customer says: "Get me a switch by tomorrow morning, or we lose the shift."

In this scenario, don't try to specify a better switch. Your job is to match the failed unit's functional spec as fast as possible, with as much delivery certainty as you can buy.

Practical playbook:

• Match the connection size and type: Is it a 1/4" flare? 7/16" UNF? M12 x 1.5? This is the #1 mismatch I see in rush orders. If you get this wrong, the switch physically won't fit.
• Check setpoint and differential range: KP series (like KP1 or KP35) are popular for this use case because they're compact and readily available. KP1 covers 0.2–1.1 bar for low-pressure applications; KP35 goes 2–15 bar for high-side use.
• Verify the electrical function: Is it a normally open (NO) or normally closed (NC) contact? In the KP series, the switch function depends on the pressure rise—make sure you get the right fallback.

Last year, a client called at 6 PM needing a replacement for a RT 116 that had failed on a rooftop chiller. Normal stock was a day away. I found a KP15 at a distributor 40 minutes away, but it had a different switch function (NC instead of NO). We wired it with a relay, paid $160 for a same-day courier, and had the chiller running by midnight. The alternative was a $6,000 shift loss.

So in this scenario, I'm buying time. The KP series is a solid match for most compressor control applications, and the availability is generally good. But verify every dimension on the phone before you drive or ship.

Scenario C: You're Stocking Spares for a Client (High Certainty Needed)

This is the "just in case" scenario. You're a plant maintenance manager or an OEM parts supplier. You want to have one or two switches on the shelf that cover the most likely failures—without tying up too much inventory cost.

This is the trickiest scenario, because you're sacrificing optimal fit for coverage. But if you choose well, you can handle 70-80% of callouts with one or two SKUs.

Best bet: The MBC 5100 for light-industrial refrigeration. The KP35 for general HVAC.

Here's my reasoning. The MBC 5100 is a compact differential pressure switch designed specifically for refrigeration. It covers 0.2 to 6 bar differential, with an adjustable differential setting. It's essentially a workhorse switch—not the cheapest, but the most reliable across common failure modes. I did a quick tally from our internal records: in the last 18 months, the MBC 5100 would have been a direct substitute for 68% of the pressure switch failures we saw in food retail (walk-in coolers, display cases).

The KP35, on the other hand, is a solid all-rounder for HVAC. It handles 2–15 bar, works with R134a, R404A, and R410A, and has a standard IP54 rating. If you can keep only one high-pressure switch on the shelf, make it the KP35.

But—and this is important—verify the refrigerant compatibility. Danfoss publishes a refrigerant list in their technical literature (Danfoss KP manual, p. 23). Not all switches are compatible with flammable refrigerants like R290 or R32. If your client uses propane-based refrigerants, you need the Atex-rated version. Ignoring this is a fire risk, not just a performance issue.

How to figure out which scenario you're in

It sounds obvious, but I've seen people misdiagnose a replacement (Scenario B) as a new engineering spec (Scenario A). The difference is simple: if you can wait three days and order the exact switch, you're in Scenario A. If you need it in 24 hours, you're in Scenario B. If you're building a stock list for future unknowns, you're in Scenario C.

Here's a quick litmus test:

• Question 1: Is the system already built? If yes, skip to Question 2. If no, you're designing—go RT or MBC.
• Question 2: Is the failed switch the only component holding up the restart? If yes, you're in urgent replacement—prioritize availability over precision.
• Question 3: Do you have a two-year contract for preventive maintenance? If yes, stock spares. Don't chase one-off switches per customer.

Most of the mistakes I see happen when someone tries to force a single switch model into all three scenarios. The KP1 is great for low-pressure on air compressors, but it's a gamble on a rack refrigeration system. The RT 116 is a tank, but it's expensive to stock as a spare. Choose based on your scenario, and you'll spend less time expediting and more time fixing.

(Pricing note: prices vary by distributor and volume; verify current pricing with your Danfoss supplier. As of April 2025, KP35 list price is approximately $35-55 USD; RT 116 is around $70-110; MBC 5100 is about $45-65.)