Danfoss RT116 vs KP Series: A Cost-Focused Pressure Switch Comparison

I'm the procurement manager at a 45-person HVAC and refrigeration service company, and I've managed our controls-component budget for six years. I've negotiated with enough vendors and documented enough POs to know one thing: before you compare Danfoss pressure switch models, you need to compare the application first.

Most of our orders fall into two families: the Danfoss RT116 pressure switch and the KP series. These are often treated like interchangeable options in the same category. They're not. And that mistake shows up on the invoice.

What We're Actually Comparing

I'm going to compare these two product families on four dimensions: application fit, installed cost, reliability and maintenance, and documentation/engineering time. Each dimension ends with a clear conclusion. At the end, I'll give you a selection checklist.

This is not a general which-is-best review. The best pressure switch is the one that matches the physical measurement you're making. The second-best pressure switch is the one that your technicians can install and service without extra parts or phone calls.

Dimension 1: Application Fit

The KP series is the workhorse for refrigeration and air conditioning compressor control. Models like the KP1 and KP15 cover high-pressure and low-pressure cut-out duties. The KP35 combines low- and high-pressure monitoring in a single housing. These are single-pressure or dual-pressure controls, not differential pressure switches.

The RT116 is different. The Danfoss RT116 pressure switch is a dedicated differential pressure switch. It compares two pressure points and reacts to the difference between them. That's the tool for filter monitoring, flow blockage detection, or measuring pressure drop across a heat exchanger. If you're running air handling units with large air filter rolls, an RT116 can trigger a service signal when the media is loading up.

I used to assume a specialized differential switch would be a premium solution for every job. In practice, it's the opposite: the specialized switch is often the cheaper solution—because it doesn't require extra components to simulate a function it was never designed for.

One caveat: the KP family also includes the KP36, a differential pressure control used for oil pressure failure protection on compressors. That's a different role. For general process differential pressure monitoring, I reach for the RT116.

Conclusion: Need differential pressure? RT116. Need compressor high/low pressure control? KP. The application fit decides most of the cost story.

Dimension 2: Installation and Setup Cost

Let's talk about the real cost comparison. I'm not going to quote list prices, because they change and every distributor has a different multiplier. Instead, think about installed cost: parts, labor, piping, wiring, and your technician's time.

In a retrofit I audited a few years ago, one vendor proposed a KP-based solution for a filter-monitoring application because the base switch had a lower quoted price. Another vendor proposed an RT116. The KP quote looked cheaper on the line item. After adding an external differential relay, extra pressure taps, and an extra hour of wiring, the KP route cost roughly 25% more than the RT116 route.

The RT116 is not always simpler to install. It needs two impulse lines, which means you need proper connection points on both sides of the filter or heat exchanger. If those points don't exist, the installation labor goes up. But if you're comparing a purpose-built differential switch against a single-pressure switch with aftermarket workarounds, the purpose-built switch usually wins on cost.

Conclusion: For differential duty, the RT116 is often the lower installed-cost option. For standard compressor control, the KP is simpler and cheaper to install. Don't pick a switch just because the base price looks lower.

Dimension 3: Reliability and Maintenance

The conventional wisdom is that an industrial pressure switch is a pressure switch. I thought that too, until I started tracking service callbacks by component type.

In our data, the KP series has been solid. It does one job and does it consistently. A spare KP switch is cheap enough to keep in stock, and replacement is a straightforward swap. The RT116 is also reliable, but it has an extra responsibility: both impulse lines need to stay clear. A plugged line can cause a false reading, which looks like a switch failure even when the switch itself is fine.

I don't have hard industry-wide failure-rate numbers, so take this with a grain of salt. In our chilled-water straining application, the RT116 units have run for four years without a calibration issue. That's a limited sample, but it matches what I've seen in other differential pressure installations.

Conclusion: Both families are dependable when they're applied correctly. The RT116 adds a maintenance point—the impulse lines—but it also protects equipment from the problems that clogged filters can cause. That's a cost trade-off worth recognizing.

Dimension 4: Manuals and Engineering Time

If you think documentation doesn't affect cost, ask yourself how many hours your team has spent staring at a confusing wiring diagram. Specifying the right pressure switch is only the first step. The installation team has to understand it.

Danfoss publishes solid technical material, but you have to look for the right document. When we first installed an RT116, I searched for the Danfoss differential pressure switch manual and used the official PDF for connection and adjustment guidance. It saved us from guessing.

The KP wiring is simple enough that I rarely open the manual twice. The RT116 takes a little more reading on the first install because the differential connection isn't as intuitive. But the manual is thorough—and a thorough manual is worth money when it prevents a miswired control.

Conclusion: Engineering time is part of total cost. Budget a little extra first-time setup for the RT116, but use the official manual to remove the guesswork.

Which One Should You Buy?

Here's my practical checklist, not a marketing answer:

• Choose the RT116 if you need to monitor the difference between two pressure points: filter loading, strainers, flow blockage, pressure drop across a heat exchanger. In my opinion, it's usually the lower total-cost route for these jobs.
• Choose the KP series if you need high-pressure cut-out, low-pressure cut-out, or dual-pressure compressor control. You don't need differential measurement for that. Paying for extra capability you won't use is the fastest way to inflate your own budget.
• Choose both if your system has two separate requirements—for example, compressor protection and filter monitoring. It's a normal system design, and the cost is justified by the protection each switch provides.

Notice I didn't say it depends and then leave you hanging. The selection is straightforward once you know the measurement you're trying to make.

Bottom Line

If you're accountable for the numbers like I am, compare total cost, not the unit price column. The cheapest quote on a switch is not the cheapest installed solution. Ask the simple question: are we measuring a single pressure or a pressure difference? That question will lead you to the right Danfoss pressure switch family faster than any product catalog.

And if your search was does the air filter affect the ac in a car, the short answer is yes—a dirty cabin air filter restricts airflow through the evaporator, so the AC output drops. But that is not the Danfoss product line I'm covering here. Similarly, if your search was is STP a good oil filter, I can't help you there—that's outside industrial controls. This article is about industrial pressure switches, and those are the ones I can help you price out.