Danfoss Pressure Switch Wiring Guide: KP36 Setup, Diagram PDFs, and Quality Checks

This one's for technicians who need to wire and set a Danfoss pressure switch without burning the workday. I've been on the quality side of these installations for over 4 years, reviewing 200+ switch setups a year, and I can tell you that most field failures don't come from the switch itself—they come from skipped wiring checks and forgotten system maintenance. So here's a straightforward, 7-step checklist for getting a Danfoss pressure switch (KP36, KP15, RT116, MBC 5100—whichever you're working with) running correctly. It's not the only way, but it's the sequence that catches the most mistakes.

Step 1: Confirm the exact switch model and function

Don't assume you have the right switch just because the housing looks similar. The Danfoss KP36 pressure switch, for example, is a differential pressure switch for air and non-aggressive gases, while the KP1 is high-pressure for refrigerants. Getting the model number into your documentation early saves a ton of confusion. Check the nameplate, note the series (KP, RT, MBC, KPI), and confirm whether the switch is adjustable or factory-set.

Step 2: Get the right wiring diagram PDF

The biggest time-waster I see is someone wiring from memory. A Danfoss pressure switch wiring diagram PDF is available for every current model in the series, and per the Danfoss installation guide, using the correct diagram is part of the setup procedure. Don't use a diagram from another model just because the terminal layout looks similar—specifically for the KP36, the terminal functions (COM, NO, NC) might be oriented differently than on an RT switch. Print the correct sheet or keep it open on your phone. And if you're ordering replacement parts, have the diagram ready so you can match the exact pressure range and electrical rating.

Step 3: Inspect the system's filters before you touch the new switch

This is the one people skip. A new pressure switch will not fix a system that's being starved by a clogged filter, and a switch that trips on pressure spikes may actually be reacting to a filter issue. So while you're in there, ask: what does air filter do in car? In automotive or industrial setups, the air filter keeps contaminants out of the compressor and the control lines. And if you're checking a vehicle with a small engine (say, an EZGO utility vehicle), verify that the EZGO oil filter is seated and oriented properly. That's a common cause of oil pressure fluctuations on these vehicles. If you're not sure which way does the air filter go, look for the arrow on the filter frame or in the housing—most filters have one. Getting this wrong can throw off the system pressure readings and make a perfectly good switch look bad.

Step 4: Wire it, but double-check the terminals

Now comes the wiring itself. Disconnect power first—I don't care if it's a low-voltage control circuit; the habit matters. Then follow that wiring diagram PDF you downloaded. For most Danfoss pressure switches, you're dealing with a common (COM) terminal and either normally open (NO) or normally closed (NC) contacts. Use a multimeter on continuity mode to confirm which terminals close when pressure rises. I've caught real installations where a contractor swapped NO and NC because they assumed the switch was normally closed when the process required it open. That miswire cost us a $22,000 pump redo when the system ran without high-pressure protection.

Step 5: Set or adjust the switch point

Setting a KP36 or similar switch is straightforward, but it's worth doing slowly. Most switches have a range spindle and a differential spindle. Turn the range spindle until the pointer aligns with your cut-in or cut-out pressure. Then set the differential to control the gap between cut-in and cut-out. Here's where I'd add a caution: the scale on the housing is a reference, not a calibration. I wish I had tracked how often the scale is off by more than 0.2 bar when we first started, but I can tell you anecdotally it's not rare. If the pressure needs to be precise, use a calibrated test gauge while you turn the spindle.

Step 6: Test the switch under real conditions

Don't skip this. With the system running, slowly bring the pressure up and watch the switch point. Does it cut out where you set it? Then bring it down and confirm the cut-in point. For a differential switch, also verify the deadband is what you intended. This is pretty much where you catch leaks in the capillary lines and bad seals—problems that have nothing to do with the switch itself. The first time I tried this, I didn't have a proper setup and almost chased a false issue for a day. Now every install gets a 15-minute functional test.

Step 7: Label the switch and log the settings

Finally, put a tag on the switch or next to it with the actual cut-in/cut-out values, the date, and your initials. Future technicians (including future you) will thank you. In our quality audits, a labeled switch is the single best indicator that the installation was done thoughtfully. It also helps when the customer wants to argue about warranty—you have a record.

When this checklist doesn't apply

This is for new installations or replacements with the same model. If you're swapping in a Danfoss switch to replace an old competitor's unit with a different wiring scheme, you'll need to adapt the steps. Also, if your system has a corrosive environment or requires explosion-proof enclosures, a standard KP36 or RT switch might not be the right choice for the atmosphere. Don't let the simplicity of this list convince you to ignore local code requirements or the manufacturer's specific installation manual. The manual is always the authority; this checklist is just the practical layer I add from the quality side.

One more thing on the filter question: if you ended up here because you were searching for what does air filter do in car, or which way does the air filter go, and you don't actually own a Danfoss switch, feel free to bookmark the answer: the air filter stops particles from entering the engine, and the arrow on the filter shows airflow direction. Also, if you're maintaining an EZGO or similar small vehicle, the oil filter needs to be tight but not crushed, and replaced on schedule. But if your actual project is a pressure switch, you're in the right place.

There's something satisfying about a panel that's correctly wired, properly set, and labeled. After the hours of hunting down the right diagram and the nagging worry about whether you set the differential correctly, seeing the switch trip exactly where it should—that's the payoff. If you follow this checklist, you'll get there without the nagging.