How Do Heated Diode Refrigerant Leak Detectors Work?

The heated diode refrigerant leak detector is quickly becoming the most common type of detector seen in the field today. Sure, there are other models such as Corona Suppression and Infrared but the good majority of tools out there are heated diode.

Here’s the question though, how exactly does a heated diode detector work? What are the Pros and Cons of these types of products? Should you get a heated diode or should you look at maybe an Infrared or an Ultrasonic detector?

The How

This type of detector works by heating the refrigerant and breaking the molecules apart. When the molecules are broken a positively charged Chlorine or Fluorine ion will appear. The heated diode will detect these ions and sound the alarm either audibly, visually, or both.

What this means is that a heated diode detector will be able to sniff out pretty much all refrigerants used today. Why? Well most refrigerants either contain Chlorine or Fluorine. Let’s take a look at some of the most popular refrigerant classes and types on the market today:

  • CFCs – Chlorofluorocarbons have been pretty much phased out from the world today due to the Chlorine that they contained. Chlorine was found to damage the Ozone every time it was released or vented. Popular refrigerants in this category include R-12 and R-502.
  • HCFCs – Hydrochloroflurocarbons are pretty much the same story. They were also phased out, more recently, due to the Chlorine that they contained. The most popular refrigerant in this category which I’m sure you have all heard of is R-22. (R-22 was the standard refrigerant for residential cooling for many years.)
  • HFCs – Hydrofluorocarbons are where things get a bit different. In an effort to save the Ozone Chlorine was removed from these new classes of refrigerants. The one constant chemical that remained though was Fluorine. (Remember, that’s the other chemical that heated diodes detect.) HFC’s are the most popular refrigerants in the world today and include the most common names such as R-134a, R-404A, and R-410A.  Chances are you if you are working on a unit it’ll have an HFC refrigerant.
  • HFOs – Hydrofluoroolefins are a newer classification of refrigerants designed in effort to replace the HFC refrigerants. Like their HFC sister HFO’s also contain Fluorine. While these refrigerants are still being developed in labs today by Honeywell and Chemours there are some you may see in real world applications already such as working on a newer automobile and finding that it uses HFO-1234YF instead of R-134a.

You may have noticed that each one of those classes of refrigerants contained one of the key chemicals: Chlorine or Fluorine. While most refrigerants have these two chemicals not all of them do.

It is worth noting that there is one class of refrigerant that your heated diode detector will not find and that is Hydrocarbons. Hydrocarbons are your natural refrigerants such as Ammonia, Propane, or Isobutane. If you’re a residential tech then you’ll probably never run into these but if you’re a chiller or a freezer tech then you probably have already run into these at a supermarket or cold storage warehouse. For these you will need a Hydrocarbon detector.

Pros & Cons

Jut like with everything else there are Pros and Cons to purchasing a heated diode refrigerant leak detector.


  • Heated diode sensors can be very sensitive even to the smallest of leaks. Some of the top models can detect leaks as small as 0.006 ounces per year. Try getting that detection level with a Corona Suppression model!
  • With this type of detector you can move the probe right to the very spot of the leak and hover over that point to detect very small leaks. Infrared detectors require you to be constantly ‘sweeping’ back and forth rather than resting in one single location.
  • The most highly rated leak detector by technicians is a heated diode. Yes, that’s right the H-10 Pro is a heated diode model.


  • The biggest con on these types of detectors are the life of the sensor. Most diode sensors will need to be replaced after only about one-hundred hours of operation. A comparable Infrared detector will see sensor life last for years.
  • If you are working in an enclosed area that is saturated with refrigerant you man end up overwhelming your sensor and shortening it’s life.
  • The heated sensor needs time to warm up before it can be used. Depending on the model this can take thirty seconds or over two minutes.

Our Preferred Heated Diode Detectors

Alright folks so we’ve gone over how these detectors work, the Pros & Cons, but now we need to review what we here at RefrigerantHQ recommend.

Whenever I recommend a product I always like to use the Good, Better, Best model. What is that? Well you see there are three different kinds of consumers or customers. There are the guys who want the cheapest thing there but still will work, the good; then there are the guys who want decent quality but they are a bit timid on the cost, the better; and then you have the guys who want the premium product, the best. The question you have to ask yourself before reviewing our choices below is what kind of consumer are you?

The Good

Signstek Refrigerant Leak DetectorSignstek Portable AC Refrigerant Halogen Gas Leakage Detector Tester with High Sensitivity for Home Use

Buy on

The Signstek refrigerant leak detector is your bare bones heated diode detector. This tool is for the homeowner, the do-it-yourselfer, or maybe even a junior apprentice trying to learn their trade. This is a cheap but still a quality detector.

The Better

Inficon Tek-Mate Refrigerant Leak Detector

Inficon TEK-Mate 705-202-G1 Refrigerant Leak Detector, R22, R410A, R134A Detects

Buy on

The INFICON Tek-Mate is a very common and high quality heated diode detector that I am sure that you will find in any HVAC shop. Most everyone knows the TEK-Mate name already and will swear by it’s accuracy. The best thing is that as I write this it is under two-hundred dollars. (Price is subject to change at any time.)

The Best

Bacharach H-10 Pro Refrigerant Leak Detector

Bacharach - H-10 PRO Refrigerant Leak Detector

Buy on

I am sure most of you already knew what was coming before you even scrolled over the Bacharach name. Yes, it’s the H-10 Pro refrigerant leak detector. This thing is hailed as the best of the best out of any and all leak detectors by technicians, mechanics, business owners, and everyone else alike. This is a premium product just be ready to pay a premium price.


In conclusion that is a brief synopsis of how the heated diode refrigerant detectors work, the benefits and drawbacks, and RefrigerantHQ’s recommended products. Thanks for reading and I hope that I was able to answer your question.