Charging by superheat

[smoke]

I've never done it before. I've always either weighed the charge in or used the pressure/temp. at the coils.

So I would like to know how to do it the "best" way.

From what I understand I take a temperature reading on the liquid line going into the evap. Then I take a temperature reading on the vapor line 6 inches from the evaporator outlet. I should have a difference of 8-12 degrees F.

Is this correct?

Thanks all,
-smoke-

[jeffcolledge]

Superheat is suction line temp minus saturated suction temp.
A temp. reading on the liquid line is used in subcooling recordings. The best place to take the superheat reading is at the inlet of the compressor. Most compressors are rated to have about 10F superheat.

[sparks]

Check here.


http://hvac-talk.com/vbb/showthread.php?threadid=21500

[frozensolid]

Remember only charge cap tube systems on superheat.

TXVs use subcooling or sight glass.

[R12rules]

Originally posted by frozensolid
Remember only charge cap tube systems on superheat.

TXVs use subcooling or sight glass.

And SUBCOOLING method is the better of the two. Especially on the new blends.



If somebody would have told us in detail what we would endure in this trade once real freon was outlawed and only blends were available .... we could have titled the book; "A Brave New World!"

[hvacbear]

Sounds like someone listened in tech school! This was the way we were taught (in the AF) it works, but make sure you read the manufacturers literature because sometimes they want 20 degrees or more.