R-12 A/C

[JHZR2]

Originally Posted By: Brad_C
Originally Posted By: Gasbuggy
I have a 92 Yukon Coupe that has a R12 system in need of charge. How do I connect propane to it?


A) You don't.
B) If you need to ask then you have much homework to do.

Pure propane has a much higher pressure curve than R12 and in hot climates may well cause rupture damage to the system. Appropriate HC refrigerants are a blend (usually of Propane & iso-Butane) which are mixed to lower the system pressure to that roughly matching R12. R290 is pure Propane.

In this chart OZ-12 represents approximately a 60/40 mix of R290/R600a (Propane/iso-Butane).
Y Axis is PSI. X Axis is temperature (C).

You can see on a hot day when condensing at 60C (pretty normal). Propane is about 100PSI up on R12. Not good.

The problem with blends is that there is a possibility of the more volatile species to escape at a faster rate than the other one. Then what?

Evacuating an HFC system is what scares me most - no shop is going to do it, and release to the air is a huge danger. Vacuuming it down is also a concern.

 

[Shannow]

Not sure on the use of "huge" in describing the risks.

 

[Brad_C]

Originally Posted By: JHZR2
R12 systems were optimized for the working thermodynamics of that fluid, which was different, and when the 134a was put in, in addition to having different pressure-temperature behaviors, it also was only filled like 75 or 80% (IIRC) as much as R134a. That makes a big difference on a hot day!


No, no, no, no, no... Like I said in my rant about HC being the same volume as R12 though it is a different weight, r134a is exactly the same.
For a given volume of liquid, r134a is 80.93% of the weight of R12. You charge by weight for the convenience of it, but the important factor is the volume of liquid in the system under steady state conditions.
So you put approximately 80% of the charge by weight when you retrofit an R12 system, but you are actually putting the same amount of refrigerant in there (liquid volume, gas volume at STP, whatever - it's the same thing).

The reason it's so [censored] as a retrofit is entirely to do with condenser performance.

 

[Brad_C]

Originally Posted By: JHZR2
The problem with blends is that there is a possibility of the more volatile species to escape at a faster rate than the other one. Then what?


You dump and re-charge. Just the same as you MUST when you fix a leaking R4xx series refrigerant like the 410a in most new A/C units. Yes the blend fractions and your performance gradually gets worse as it leaks away. If you have a leak you need to be recharging before or as soon as you notice the performance degradation anyway or you'll impact oil circulation and damage the compressor.

Originally Posted By: JHZR2
Evacuating an HFC system is what scares me most - no shop is going to do it, and release to the air is a huge danger. Vacuuming it down is also a concern.


Twaddle. Don't hold your lit cigarette at the discharge outlet of your vacuum pump and you're fine. Once you've recovered the remaining refrigerant (you know, that procedure where you pull the refrigerant from a mostly sealed system - after all the leak is probably why you're doing this - into a fully sealed system - the recovery machine and cylinder) the amount of gas left in the system is so small you'd have to be discharging it into a shoe box to reach the flammability limit. You do actually recover your refrigerant don't you?

Plenty of shops in Aus have been servicing HC systems for 20 years now. Don't do dumb stuff and you're fine. Just like you don't want naked flames when you de-pressurize an injection system.

[censored] you discharge more gas out of your BBQ before you hit the igniter than your vacuum pump will pull out of the system.

 

[JHZR2]

Originally Posted By: Shannow
Not sure on the use of "huge" in describing the risks.


If you press a schrader down and dump the system (as you can be sure some folks will), Id say the risk of a Darwin award are there.

If you evacuate a used bbq tank, manage to transfer it in there, and then use it in your grill? Likely not risky.

Here in the states, a typical automotive shop is not set up for these materials, so wont be touching it. Its different than Australia. A CFC/HFC, absolutely would be recovered - a shade tree person working on their vehicle? Perhaps not.

Im not going to be one to release 1 lb of propane in my general vicinity, no matter how "safe" some may claim.

The setup to recover HCs from a car is a reason Ive not gone that route. Ive fixed my R12 systems so they dont leak, and maintain an R-12 charge, plus an R-12 stockpile.


That said, I'm also not opposed to HC refrigerants, if the mix is right.

 

[JHZR2]

Originally Posted By: Brad_C


Originally Posted By: JHZR2
Evacuating an HFC system is what scares me most - no shop is going to do it, and release to the air is a huge danger. Vacuuming it down is also a concern.


Twaddle. Don't hold your lit cigarette at the discharge outlet of your vacuum pump and you're fine. Once you've recovered the remaining refrigerant (you know, that procedure where you pull the refrigerant from a mostly sealed system - after all the leak is probably why you're doing this - into a fully sealed system - the recovery machine and cylinder) the amount of gas left in the system is so small you'd have to be discharging it into a shoe box to reach the flammability limit. You do actually recover your refrigerant don't you?

Plenty of shops in Aus have been servicing HC systems for 20 years now. Don't do dumb stuff and you're fine. Just like you don't want naked flames when you de-pressurize an injection system.

[censored] you discharge more gas out of your BBQ before you hit the igniter than your vacuum pump will pull out of the system.


Therein lies the issue - in the USA, nobody has the facilities and means for recovering and servicing HCs (I had a typo where it says HFC above, obviously).

Heck, there are people who dump CFC and HFCs to the air without recovery, despite any "law", you think theyll care about recovering HCs?

If it was institutionalized in the USA, equipment would come about to the mainstream auto tech. Given that its forced underground, Im not seeing the chance as great, unfortunately.

 

[JHZR2]

Originally Posted By: Brad_C
Originally Posted By: JHZR2
R12 systems were optimized for the working thermodynamics of that fluid, which was different, and when the 134a was put in, in addition to having different pressure-temperature behaviors, it also was only filled like 75 or 80% (IIRC) as much as R134a. That makes a big difference on a hot day!


No, no, no, no, no... Like I said in my rant about HC being the same volume as R12 though it is a different weight, r134a is exactly the same.
For a given volume of liquid, r134a is 80.93% of the weight of R12. You charge by weight for the convenience of it, but the important factor is the volume of liquid in the system under steady state conditions.
So you put approximately 80% of the charge by weight when you retrofit an R12 system, but you are actually putting the same amount of refrigerant in there (liquid volume, gas volume at STP, whatever - it's the same thing).

The reason it's so [censored] as a retrofit is entirely to do with condenser performance.


There's a lot to it, yes I said mass flow (which implies liquid content and mass flow of liquid entering the evaporator) in my other post, but a complete assessment must be made. Since R134a has a higher heat of vaporization, if it were merely the matter of the same amount of liquid, the cooling would be really close (since 134a has that higher heat of vaporization). So I DO agree with you that condenser performance has a lot to do with this (as I believe I said before).

Its a common mention that R-134a is "less efficient" than R-12 (despite having a higher heat of vaporization). One needs a decently larger condenser area, and the pressure ratios that the compressor must deal with differ somewhat.

If:

COP = Tcold/(Thot-Tcold)

and,

Capacity = COP * mrefrig * Delta H Compressor

(COP times mass flow times enthalpy from compression; COP is increased by an increase in Tcold or a decrease in Thot)

We know that an r134a system runs at higher pressure. The pressure ratio is about 25% higher to obtain the same COP. So with the same condenser surface area and heat transfer characteristics, and a lower mass flow, and higher compression energy (due to higher pressure ratio), capacity will be lower for the same system.

We have approximately (for R-134a):

20% less mass
30% more energy removed per g of refrigerant vaporized
25% more work needed to pressurize the material (maybe not quite since the vapor density is less??)

The condensers and compressors were optimized for the pressure ratios and behaviors of R-12. If it was just a matter of the same amount of liquid being in there, the performance would be good/better.

I think were in violent agreement actually...

 

[ATS-V]

Originally Posted By: rooflessVW
I have converted all of my R12 cars to propane.

Winter mix Coleman's, use a little bit less than you would with R12.


40% of original charge by weight

 

[DoubleWasp]

Originally Posted By: Jarlaxle
Thought so. Dude...pour out the booze, flush the pills, and get some help.


I don't have that problem just because you do. Get out of your sister's bed and find something constructive to do.

 

[DoubleWasp]

Originally Posted By: JHZR2


The problem with blends is that there is a possibility of the more volatile species to escape at a faster rate than the other one. Then what?

Evacuating an HFC system is what scares me most - no shop is going to do it, and release to the air is a huge danger. Vacuuming it down is also a concern.


Huge danger? I'm guessing you have never owned and maintained a fleet of equipment with propane fueled engines.

When you go to service one of those systems, there is no recovery equipment. You're going to purge that system straight into the air, or you're not going to fix it.

Nobody who maintains or operates this equipment considers it a "huge danger".

 

[Shannow]

Agreed, with R12 and 134 being equivaent to 10,000 and 1,400 lb/lb of CO2, they are of course regulated and recovered.

Propane is nothing like that.

I had a Propane powered ute, and had zero issues during maintenance, you just don't do dumb things...same with my HC filled A/Cs.

 

[Jarlaxle]

Originally Posted By: DoubleWasp
Originally Posted By: Jarlaxle
Thought so. Dude...pour out the booze, flush the pills, and get some help.


I don't have that problem just because you do. Get out of your sister's bed and find something constructive to do.


That post makes me wish it was still legal to challenge someone to a duel.

 

[DoubleWasp]

It's to your benefit. If we still had duels, you would have been gone a long time ago.

 

[SteveSRT8]

Originally Posted By: DoubleWasp

Nobody who maintains or operates this equipment considers it a "huge danger".


Exactly, or every marina, warehouse, home improvement store, etc., with a forklift I ever went to would have blown up by now!

 

[HotDog15]

Originally Posted By: Jarlaxle
Originally Posted By: DoubleWasp
Originally Posted By: Jarlaxle
Thought so. Dude...pour out the booze, flush the pills, and get some help.


I don't have that problem just because you do. Get out of your sister's bed and find something constructive to do.


That post makes me wish it was still legal to challenge someone to a duel.


I will duel with you

Do you challenge me to a duel?

 

[Jarlaxle]

Originally Posted By: DoubleWasp
It's to your benefit. If we still had duels, you would have been gone a long time ago.


Probably...but so would the other guy. I choose flamethrowers at one pace.

 

[DoubleWasp]

Originally Posted By: HotDog15
Originally Posted By: Jarlaxle
Originally Posted By: DoubleWasp
Originally Posted By: Jarlaxle
Thought so. Dude...pour out the booze, flush the pills, and get some help.


I don't have that problem just because you do. Get out of your sister's bed and find something constructive to do.


That post makes me wish it was still legal to challenge someone to a duel.


I will duel with you

Do you challenge me to a duel?

Funny thing about duels is that the advent of firearms reduced the danger element. Pistols were so bad, nobody could hit anyone.

One Russian man was in 596 duels before being killed by a man who was actually in shock he hit him, as he intended only to demonstrate his grievance and desired no injury.

 

[wtd]

My daily driver 92 Cavalier still uses R12. I did replace the compressor, Accumulator, Condensor, OT, and all O-rings in the system quite a few years ago.

My other 92 Cavalier I converted to R134 before I had my 609 cert and it still blows cold 10 years later. I have a mostly full 50 lb tank of R12 and a few cans so I should be good for awhile.

I plan on repairing the system in my 70 Monte Carlo at some point and will keep it R12.

Wayne