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

[Ron Frazier (ALE)]

Phil,

That's some cool information you posted.  Nice website.

So, if you wanted to top off a system without vacuuming it down, for a 
given car and a given outdoor temperature, how would one determine what 
the high side and low side pressures are supposed to be?  The can I was 
using has an adjustable gauge for low side pressure correlated to 
ambient temperature, which seems fairly accurate.  But, apparently, that 
means little in regard to the level of refrigerant in the system.

You said r134a was unregulated for personal use.  That's not totally 
true.  The following epa faq says it's illegal to knowingly vent r134a 
to the atmosphere.

http://www.epa.gov/ozone/title6/608/faq.html

I find this fascinating from a scientific point of view whether I ever 
work on my car or not.  I have had an interest in alternate energy for a 
long time.  When I get time, space, and money ... someday ... I want to 
do experiments with low temperature heat engines to use solar power or 
even ambient heat in my attic (which is, in effect, solar) or geothermal 
energy.  I would really love to be able to run an engine on a 100 degree 
F temperature delta.

http://en.wikipedia.org/wiki/Minto_wheel
http://en.wikipedia.org/wiki/Drinking_bird
http://en.wikipedia.org/wiki/Stirling_engine
http://en.wikipedia.org/wiki/Ocean_Thermal_Energy_Conversion

Sincerely,

Ron


On 8/16/2013 1:13 AM, Phil Turmel wrote:
> 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
>
>    


-- 

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Ron Frazier
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