[DML] Re: A/C - switch back to R12?

["Harold McElraft" <hmcelraft@xxxxxxx>]

A closed system should not be affected by the atmospheric pressure. 
Generally 134 should run about 10-15% higher pressures than R-12 
depending on the condition of the system components. R-12 2.25 lbs 
134 2 lbs. The chart in the shop manual tends to be on the low side 
for ambient air temp. I think for stationary checking, the ambient 
air temps on the chart should all be about 10 degrees lower for each 
grade - i.e. 60 SB 50, 70 SB 60, etc. You should monitor the low side 
pressure and have a temp gauge in the center outlet typically the 
compressor should cycle (the higher the ambient air the less frequent 
the cycles) with R-12 around 25-28 psi and 40 degrees at the outlet 
(R-12). R-134 may be 42 degrees at the outlet - not too far off R-12. 
Good cooling fans will make the difference for 134.

All of this assumes a proper functioning, properly prepared system.

The system was made for R-12 - if you can't afford to fix it so it 
will hold R-12, as it is expensive - use 134 and re-charge every 
season - no worse than an extra oil change. If you are going to the 
trouble to fix up the system to be nice and tight to hold freon - I 
would recommend staying with R-12.

Harold McElraft - 3354



--- In dmcnews@xxxxxxxxxxxxxxx, "John Hervey" <john@...> wrote:
>
> Andy, If I'm not mistaken your are in the northwest. It could be 
different
> for the altitude. I would leave it to the gauges which will tell 
the real
> story as to what is going on in your system.
> John
>   
> 
> -----Original Message-----
> From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On 
Behalf Of
> Soma576@...
> Sent: Friday, March 16, 2007 2:25 PM
> To: dmcnews@xxxxxxxxxxxxxxx
> Subject: Re: [DML] A/C - switch back to R12?
> 
> Hi John,
>  
> Can you tell me the target pressures for the A/C system and at what 
ambient
> temperature they should be read at, for both R134a and for R12?
>  
> Thanks!
> Andy 




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