MVS Forums member Jason Reed posts a fantastic write up on PTC valve electricals and function for turbo cars. PTC = Positive Temperature Coefficient.
I always wondered what was inside the PTC valve and how it worked electrically, so I decided to take apart one of the ones I harvested from the junkyard a few months ago.
I removed the rubber bushing by prying it up and off. Then I used a hacksaw to slice down one side of the main PTC tube. While I was sawing the last bit of the side, when the blade dug into the bottom piece it popped off. The bottom piece is also copper and was soldered onto the copper tube.
On the side of the main copper tube is a small 2mm diameter hole that aligns with the external small vacuum nipple. I was surprised to see how small this hole is, but when I checked the inside diameter of the vacuum nipple, it was also 2mm, so they are matched.
Next I removed the copper wall from the side of the PTC with the electrical connector. I had to pry a bit with a small flat screwdriver and I heard a cracking sound as I pried it apart to reveal the PTC heater element.
The cracking sound was from breaking the solder joints between the copper wall and the contact pin and PTC disc. I measured the resistance from the surface of the disc to the pin 2 in the connector and got ~20 Ohms, which was the resistance between the pins before I took it apart. This indicates that the resistive element in the PTC valve is the disc. The disc is soldered to the copper wall and conducts heat to the copper wall and thus to the gas passing through the PTC tube. It’s interesting that the copper wall is itself part of the electrical circuit.