how do you make the a/c colder?

["R. Cummings" <cumm@flash.net>]

Original Message
>Hi Adam;
>
>    You lose 20% of the cooling capacity when you change from R-12 to
>R-134a. In addition, the pressure generated by the R-12 compressor is not
>high enough to take full advantage of the R-134a characteristics.
>    BTW, R-134a is a mixture of propane and isobutane. Something to keep in
>mind in a front end collision with that condensor hanging out in front. The
>automotive engineers apparently believe the risk is acceptable, but I would
>think there is a good chance of a fireball with a couple of pounds of
>barbecue fuel spewing out of a ruptured condensor.
>    I don't know of a way to make the system run colder if it is properly
>charged and the propane/isobutane mixture is right. One of the problems with
>R-134a is that the isobutane is lost preferentially and the mixture gets out
>of proportion, resulting in loss of cooling capacity. This apparently takes
>3-4 years and the system has to be drained and re-charged. Fortunately,
>R-134a is cheap.
>
>HTH
>
>Fred Munro
>
Wow!! How do these rumors get started. R134a is NOT a mixture and it is not
flamable. Many states have laws that flamable refrigerants may not be used
in mobile A/C applications. R134a is the ONLY replacement refrigerant
recommended by the vehicle manufacturers.

There are some SNAP approved replacements that have 4 or 5% butane to carry
the oil but in that quantity is not considered dangerous.

R134a runs about 20 psig higher than R12 on the high pressure side for the
same refrigerant temperature but hose life and compressor life are as much a
function of temperature as pressure.

We have not found a 20% cooling capacity loss with R134a unless the original
condenser is extremely marginal. If that is the case an additional condenser
fan usually cures the problem.

It requires about 15% less R134a to charge a system than R12 so it is easy
to overcharge if not paying attention. 

Bob Cummings   87 Coupe GT