[DML] Re: R12 to R134 Conversion Help
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[DML] Re: R12 to R134 Conversion Help

Absolutely correct on all counts. The only thing to really add to that are considerations for other environmental factors and the impact that they'll have upon the Air Conditioning System's efficiency.

Certainly as the ambient temperature outside of the car increases, the temperature of the Evaporator Coils are going to increase as well because the external air is already so saturated with heat that it cannot absorb as much heat from the Condenser when the heat exchange occurs as the air is drawn across it. A drop-in R134a conversion where no VOV has been installed, nor where the Low Pressure Switch has been adjusted will certainly affect cooling, and in the case of older cars and trucks that use clutch-driven fans it can even hinder cooling. If the Orifice Tube doesn't allow proper flow at idle, and the ambient temperature outside is cool enough NOT to engage the engine fan, there won't be sufficient air flow to keep the A/C working properly, not to mention that the flow of refrigerant has been greatly hindered, hence the lack of cooling efficiency that so many people have experienced. So in older cars without an auxiliary fan you definitely will have problems if you get stuck in traffic.

Another factor is going to be radiation from sunlight. If you live in an area such as The Mojave, Sonoran, or Saharan Deserts, it doesn't matter if you use R-12 or R-134a, you're going to need to tint your windows. It's a fact. A tint reduces the amount of heat from the sun that enters your car and keeps it cool not just while parked, but while you drive as well. It has to be done, otherwise the continuous heat from the sun will increase cooling times as well as hinder cooling because it'll heat your skin back up as the cool air cools it. That's not going to be R134a's fault.

Plus we're talking about a DMC-12. This isn't like we're trying to cool the same volume of passenger area as even a compact sedan, let alone a giant Suburban.

Like I say, I agree with you wholeheartedly. The thing that I'm questioning is R-134a's cooling ability within itself. Not just the Capacitance of R134a itself, but the conditions in which it is installed.

The findings of the EPA and their partners for a successful conversion over to R134a are as follows:
1. You need to adjust the cycling switch counter clockwise to 21 PSI cycle off.
2. High Side pressures remained almost the same on FWD Vehicles, and only increase by 10-15% on RWD vehicles.
3. At speed, R134a actually produced COOLER duct temperatures than R12.
4. At Idle R134a on SOME cars MAY be 2-4ºF warmer.

The only loss in efficiency that we're seeing here is honestly that 2-4ºF. A 10ºF increase in ambient outside temperatures will cause a greater drop in duct temperatures than that, not to mention that even in triple-digit temperatures we're still talking about duct temperatures less that 50ºF.

Now these readings were taken on cars with fixed Orifice Tubes. So as a counter to that, there is the Variable Orifice Valve that replaces them. With a VOV you can actually drop the temperatures anywhere between 5-30ºF at idle (depending upon the source of info). So that not only counters the tiny loss of cooling efficiency, but can possibly increase it's capacity beyond that of R12.

Take a look here for yourselves:

Like I've said before, I'm not advocating anyone convert a car to R134a just because they can. If you've got a car that only needs a minor amount of servicing, and it's cheaper to just recharge the A/C system with R12, by all means just do that. Now on the other hand if you're having to rebuild an entire A/C system from the ground-up and have to buy new hoses and a compressor anyways... Well in that case it just makes more financial sense in the long run to make the switch.

Though whose to say that we might not have another choice right around the corner within the next year...

vin 6585

--- In dmcnews@xxxxxxxxxxxxxxx, "jtrealtywebspannet" <jtrealty@...> wrote:
> Air conditioning works on the principle of heat flow. The amount of heat moved by the A/C is a function of the amount of heat the refrigerant can absorb per unit lb and all of the inefficiencies involved with a mechanical system.


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