[ale] [WAY OT] WARNING - diy car ac recharge kits can be dangerous

[Phil Turmel]

On 08/15/2013 11:38 PM, Ron Frazier (ALE) wrote:

> The container you're talking about is functionally no different from the
> can that I had.  Based on what I read, the only safe way to ensure the
> proper amount of refrigerant is in the system is to vacuum it down and
> put the refrigerant in by weight.  Also, you have to make sure the
> compressor has adequate oil in it.

Yes, if you use a vacuum pump to draw a system all the way down, you do
have to add oil.  And the spring scale I mentioned is to weigh the tank
as you draw from it.

> Are you saying that there is a safe way to "top off" without
> overcharging and potentially creating a dangerous situation and without
> doing a full vacuum down?  Obviously, monitoring the low side pressure
> is not adequate.

That's why commercial gage manifolds have both high- and low-pressure
hoses and gages.  Yes, monitoring both high- and low-pressure
simultaneously (compressor running), you can safely top off.

Thermodynamically, the key is that the high- side has to reach a
pressure corresponding to a radiator (condenser) temperature high enough
to permit heat transfer to ambient.  The higher the outside temperature,
the higher the high- side has to go before the A/C system will cool at
all.  200psi or so.  The car's cycling switch holds the low side near
30psi.  If the rest of the system is perfect, that gives you ~32F in the
vents while rejecting heat at a ~130F radiator.

http://www.csgnetwork.com/r134apresstempconv.html

> On a side note, don't you have to have to have a business license to buy
> from msc or grainger?

Nope.  But my corporation does get 10% off. :-)

Phil