AC receiver drier - what is 3rd port for?

[NathanR]

AC receiver drier - what is 3rd port for?

Could I use this to install a high pressure switch?

[Synchro Joe]

No expert here, but I have seen trinary switches installed on the receiver/drier. Not sure if there's an advantage to that location or not. Lots of A/C gurus here that can best respond to your question. Vintage Air makes one I know as a friend of mine has their set up in his old Chevy.

[NathanR]

I think the advantage is, I don’t have to install an additional port if the one on the RD would fit a switch. Wonder what the size of the port is...

[Steve Marshall]

Where is the fan located that you are going to run on the switch? Are you also going to use it for under/over pressure safety on the compressor? You can run it right off the compressor. This T adapter will enable that. Check the size. There are two different size high side ports.

https://coldhose.com/media/catalog/product/cache/1/image/39a31c89d93b1f0e8473dc2722e8793f/m/t/mt4047_1.jpg

[kuehl]

Originally Posted by NathanR

AC receiver drier - what is 3rd port for?

Could I use this to install a high pressure switch?

The 6 mm threaded hole on the top of the drier manifold is a 'blind' hole, it does not port into the drier or refrigerant circuit. It could be used for a temperature switch; some 70's 911's did have them.

How could you use it? Well, there is corresponding temperature/pressure relationship.
For example, R134a at say 300 psi is about 160F. In theory you could have a temperature switch turn on or turn off something. However, you'd be measuring the temperature/pressure far ahead in the system flow and things could be a bit 'late' for what you intended. A better design is simply an inline switch port off high side of the system between the compressor and the deck lid condenser.
Say for example the pressure switch built into the compressor to deck lid condenser hose