1963 Jeep A/C

[Mikel]

Hello all,
I have a 1963 Jeep J300 pick-up truck. Years ago I transplanted an A/C unit from a '68 Wagoneer into my truck and finally I was able to piece it all together.

My unit is like this one:


I replaced all lines, dryer/accumulator, condenser (parallel flow), sanden compressor... I'm running R152A. Low side pressure is 40PSI, high is only 80PSI at idle.

The interesting thing is that even with such a small pressure differential, it cools reasonably well. Today it was 90F and humid and I was quite comfortable inside. It just takes a long time to cool the -not so well insulated- cabin. I can't help but think that I'm missing on a lot of performance, which is badly needed when the sun hits the cabin dead on (no tinting or filtering).

Is my TVX (I'm assuming) expansion valve stuck open? (this I did not replace) Unfortunately the expansion valve is really hard to reach or photograph. Any ideas?

Thanks.
Mikel

[Mikel]

Is there any other explanation to my low pressure differential other than a bad expansion valve? Could a new Sanden be bad? If so, can it be tested? I'm tempted to pinch a line and see if pressure rises.
Thanks.

[bohica2xo]

R152a is not an automotive refrigerant. There is no real data regarding it's use in MVAC.

You don't mention what type & how much oil you have in the system.

The evaporator and TXV are R12 items, and using something with a different P/T curve will give different results.

Was the system evacuated before charging?

[Mikel]

6 oz of PAG 150 and yes, it was evacuated.
Thanks.

[bohica2xo]

Well since you have PAG in it already, you can call your pressure check with keyboard duster a success.

Now evacuate it & charge it with 134a & it should work just fine.

[Mikel]

I was under the impression that R152A worked better in old R12 systems that R134A...?
Thanks.

[bohica2xo]

R152a is not used in any commercial system. I don't know of any published P/T charts for 152a in refrigeration. R152a is a Flammable Refrigerant

Let's start with the basics. We measure refrigerant charges by weight, because there is no easy way to measure out 15 ounces of liquid. Old guys like me have a Dial-A-Charge that can actually do both. Because the common refrigerants have a known density we can use either measurement. But there certainly IS a liquid level that is correct for the system.

Refrigerant heat capacity (Enthalpy) is expressed as an energy unit over a mass unit. Like kJ/Kg or Btu/Lb. So the density of the refrigerant is important.

134a has an Enthalpy of 300 kJ/KG R152a has an Enthalpy of 330 kJ/KG On that single property, 152a would seem to be "better". Until you consider the DENSITY of the two gasses.

134a is 1.225 grams / cc. But R152a is only 0.90 grams / cc. Not so good. by quite a margin.

So to move an equal ammount of heat you need 1.36 times the volume of a proper 134a charge when attempting to use R152a. There is no extra room in the system for a 36% overcharge. The expansion device is 74% of the area it needs to be, etc.

Certainly a system could be engineered to run R152a from the beginning. But if you plan to run flammable refrigerant in your car, go straight to the HC blends - they can mimic R12 or 134a easily enough. I think I will just stay with non-flammable refrigerant n my car.

[Mikel]

Thank you. I will try R134A this weekend.

[Mikel]

I tried R134A and it's been a noticeable improvement over R152A. Not to modern car standards, but quite acceptable in 90 deg. weather.
Thank you.

[bohica2xo]

Post the pressures & temperatures - perhaps there is more cooling available.