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

Fri Aug 16 11:57:50 EDT 2013

IF you KNOW:

1. the total volume of the tubing on both high and low pressure sides
2. the pumping rate of the compressor
3. the ambient air temp
4. the cold-side coil temp
5. the hot-side coil temp
6. the specs of the particular refrigerant
7. the total volume of oil in the system
8. the somewhat messy thermodynamic equations
9. differential equations

you CAN calculate what the pressures should be and generate pressure/temp
curves to extrapolate your data with.

There's a reason no one does it that way. The old pressure method was
unreliable and will cause damage to modern, high-efficiency systems. About
the best you can do is to use a high/low gauge and make sure that you are
below the max on the high and between the min/max on the low. Get the low
side too high and you'll freeze up the coils or crap out the compressor
trying to compress a flow that's partially liquid.

On Fri, Aug 16, 2013 at 11:41 AM, Ron Frazier (ALE) <
atllinuxenthinfo at techstarship.com> wrote:

> 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<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/Minto_wheel>
> http://en.wikipedia.org/wiki/**Drinking_bird<http://en.wikipedia.org/wiki/Drinking_bird>
> http://en.wikipedia.org/wiki/**Stirling_engine<http://en.wikipedia.org/wiki/Stirling_engine>
> http://en.wikipedia.org/wiki/**Ocean_Thermal_Energy_**Conversion<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<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
>>
>>
>>
>
>
> --
>
> (PS - If you email me and don't get a quick response, you might want to
> call on the phone.  I get about 300 emails per day from alternate energy
> mailing lists and such.  I don't always see new email messages very
> quickly.)
>
> Ron Frazier
> 770-205-9422 (O)   Leave a message.
> linuxdude AT techstarship.com
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