Danfoss Pressure Switches: An Office Administrator's FAQ for Getting Orders Right the First Time

Why I'm writing this down

I'm the office administrator at a 350-person company. I handle all the non-production purchasing—MRO supplies, office goods, maintenance parts. Roughly $180K annually across 8 vendors.

In 2021, someone from engineering sent me a requisition that said "Danfoss KP35 pressure switch." I typed it into our supplier portal, found 14 variants, picked one, and hit submit. Then crossed my fingers.

That switch had the wrong port connection. Three weeks for the return and replacement. The maintenance tech was nice about it. I still felt stupid.

Since then I've ordered 40+ batches of pressure switches. I've made fewer mistakes—not zero. Here's what I wish someone had told me.

How do I know whether we need a KP, RT, or MBC series?

If you're not an engineer, the best thing you can do is learn the broad differences and then throw the specifics back to whoever wrote the requisition.

• KP series—this is the bulk of what I order. HVAC, refrigeration, regular industrial control. Differential, low, high pressure. If a requisition says "KP," it's likely HVAC or refrigeration.
• RT series—bigger, heavier industrial use. Mostly I see these on older equipment in the shop. Sturdier. More expensive.
• MBC series—specific low-pressure applications. I see fewer of these, but when someone mentions "filter monitoring" or "fan status," it's worth asking if they need MBC.

Most buyers focus on which series to order and completely miss a more important question: where is this switch actually being installed, and what pressure range is it measuring? That answer determines the series far better than any catalog description.

What do I do when the requisition just says "Danfoss pressure switch"?

Happens every few months. Someone copies half a description from a work order system, or assumes everyone (including me) knows the rest.

Here's what I send back:

1. Which series? (KP, RT, MBC)
2. Full order code including the suffix? "KP35" alone isn't a complete part number—it's a family name.
3. Port size—G1/4, G3/8, or 1/4 NPT? (Get this wrong and the switch won't fit, no matter how good it is.)
4. Reset type—automatic or manual? (Manual reset switches have a button you press once.)
5. Electrical rating—SPDT or SPST, and operating voltage?

If they can't answer all five, I don't place the order. Full stop. Waiting for that information is cheaper than the return shipping, downtime, and the awkward conversation when the replacement doesn't work either.

What's the difference between all those KP35 variants?

This one burned me early on. The KP35 is a differential pressure switch commonly used in HVAC—filter monitoring, fan airflow, chiller differential pressure. But within that name, there are different port connections, mounting brackets, and reset options.

Some of those variants look nearly identical on a supplier's product page. The only difference might be the termination or whether it comes with a bracket.

If your requisition just says "KP35," treat it as incomplete. Ask for the full order code. The extra 30 seconds of clarifying that before you submit an order beats three weeks of wait time after you get it wrong.

How can I tell a genuine switch from a counterfeit?

Counterfeit industrial components are a real problem. I'm not the person who's going to take a switch apart and tell you what's inside. But from a purchasing angle, three habits have helped me avoid issues:

Buy from authorized channels. If a supplier offers a Danfoss switch at 40% below everyone else's price, that's not a bargain—it's a question mark. Someone is making up that gap somewhere.

Match the serials to the packaging. Genuine Danfoss switches have traceable serial numbers. The print quality is something you can verify physically.

Start small. If a new supplier is offering a good price on the right part, order a small test batch before you commit to a full production quantity. Test batches are how I learned which suppliers are reliable without risking a full order.

What documentation should I ask for before placing an order?

I ask for these every time, and I've stopped apologizing for it:

• Datasheet—including any relevant switch-specific performance data
• Wiring diagram (critical when the wiring isn't obvious or the terminal layout has changed)
• Declaration of conformity—CE marking where applicable, UL if relevant
• Warranty terms—specifically, what's covered and for how long

The wiring diagram was my blind spot. I once received a switch whose terminals didn't match the old one—took me two hours and a favor from a maintenance tech to figure out how to wire it. Now I ask for the diagram upfront and attach it to the work order so the tech can check it before installation.

What does a wrong order actually cost?

Let me tell you about the time I tried to save money.

I found a substitute switch that looked compatible—same pressure range, similar physical size—for about $12 instead of the $50 I usually pay. Ordered ten. The return and reorder cost me three weeks and one very annoyed maintenance manager.

I thought the supplier was cheaper because they were running a promotion. Actually, they were cheaper because it was a slow-moving version and the replacement parts weren't interchangeable with our existing setup. That discount was a symptom, not a cause.

Ten switches at $12 looked like $120. The rushed reorder, return shipping, and downtime pushed the real number closer to $800. A lesson learned the hard way: a cheap part without proper documentation isn't a bargain—it's a delayed problem.

So what's my pre-order checklist now?

I built this over two years. It's saved me from repeat mistakes more times than I can count.

1. Full order code, including all suffixes
2. Port connection and size matched against the existing piping or manifold
3. Reset type (automatic or manual)
4. Electrical contact type and voltage
5. IP rating—especially relevant for outdoor or wash-down environments
6. Datasheet and wiring diagram obtained and attached to the internal work order
7. Supplier checked for authorized distribution status (if new)
8. Test batch ordered for any new supplier or variant

That's about 5 minutes of work. The first time I ran the full checklist and pushed through an order without a single follow-up call—that was satisfying. Not dramatic. Just clean. Exactly what a purchasing process should feel like.

Most ordering mistakes are prevented before you click submit. A few minutes verifying now beats a week fixing your order later.