GASNER wrote:

At room temp., (i.e., haven't been running it for an hour), the pressure will
be the vapor pressure of the stuff at that temp. (IF it is not so low on fluid
that there is no fluid at all left). You have to look up somewhere what the
vapor pressure of each is. (I used to know, but that was a long time ago.)

That is correct. If you have a thermometer you can also connect your gages and
measure the temperature at the evaporator and the condensor with the system
running. Most gages have temperature indicators for different refrigerants such
that you can read the low side and high side temperatures directly. Believe me,
its is hard to mistake R12 for R22, because the pressures are much different.

I think that the stuff for cars is the one with the least pressure for a given
temp since it is so damn hot under the hood of a car.

Actually, automobiles used to use R12 which as you stated has a lower vapor
pressure than R22. For example, at 100 degrees F R12 is at ~115 PSI, while R22
is at ~200 PSI. R502 at 100F would be ~215 PSI.

Since 1996 autos sold in the USA use R134A. R134A at 100F is ~124 PSI which is
higher than R12, but much lower than R22 or R502.

I have gauges and an electronic leak detector, and I would fix my freezer, but
. . . how do people get freon today without a licence?

(Not that 'I' would do it if it were illegal. Just wondering about how 'other'
people do it.)

Earl

Well, you can buy R134A without a license at auto parts stores. There is a non-controlled
R22 replacement marketed as (I think) Puron. According to my home AC man there is also now
a non-controlled drop-in replacement for R12, but I don't know what it is called.

What is in your freezer?

Don W.