AC with Propane- Staying Alive - Page 6 - PeachParts Mercedes-Benz Forum

Matt L · #76 07-03-2009, 12:52 PM

Look at the temperature-pressure curves of each material, as well as the critical temperature. Propane alone will give you too much head pressure. If your system were designed for propane, it would work not just good but great.

Hardware-store propane is pretty wet. Your grill doesn't care about a bit of water in the fuel.

Regardless of what the Duracool and Enviro-Safe makers say, moisture inside your AC system is indeed bad. And as for the instructions to let AIR into the system (or not pull a complete vacuum, which is the same thing), well I just think that's silly.

CWW · #77 07-03-2009, 04:59 PM

Quote:

Originally Posted by Matt L

Look at the temperature-pressure curves of each material, as well as the critical temperature. Propane alone will give you too much head pressure. If your system were designed for propane, it would work not just good but great.

Hardware-store propane is pretty wet. Your grill doesn't care about a bit of water in the fuel.

Regardless of what the Duracool and Enviro-Safe makers say, moisture inside your AC system is indeed bad. And as for the instructions to let AIR into the system (or not pull a complete vacuum, which is the same thing), well I just think that's silly.

When you're talking about excessively high head pressures, you're not figuring into the equation that you use significantly less hydrocarbon refrigerant than you would R134.

So you'd be right, if you would actually use 2lbs of propane to replace 2lbs of R134. But you don't. You only use .5lb or so. The pressures aren't an issue, because of the reduced volume allowable by propane's higher efficiency. It's a total non-issue. Your actual head pressures with hydrocarbons will actually turn out to be significantly lower than with R134a.

Matt L · #78 07-03-2009, 09:05 PM

Quote:

Originally Posted by CWW

When you're talking about excessively high head pressures, you're not figuring into the equation that you use significantly less hydrocarbon refrigerant than you would R134.

So you'd be right, if you would actually use 2lbs of propane to replace 2lbs of R134. But you don't. You only use .5lb or so. The pressures aren't an issue, because of the reduced volume allowable by propane's higher efficiency. It's a total non-issue. Your actual head pressures with hydrocarbons will actually turn out to be significantly lower than with R134a.

I am talking about pressure-temperature curves and critical temperatures, and specifically not saying that you use the same quantity of propane as you would R12 or R134a.

Adding isobutane (R600a) reduces the pressure quite a bit. That's why it is added to propane. But any leaks will not leak the two gasses at the same rate, which is why it is not a good idea to top off a blend. You should always reclaim and recharge instead. Then dispose of the reclaimed refrigerant properly.

Now, I don't see anything in the EPA regulations which prevent me from disposing of such a blend in my backyard gas grill. Perhaps there is something there though.

CWW · #79 07-04-2009, 11:00 PM

Quote:

Originally Posted by Matt L

I am talking about pressure-temperature curves and critical temperatures, and specifically not saying that you use the same quantity of propane as you would R12 or R134a.

Adding isobutane (R600a) reduces the pressure quite a bit. That's why it is added to propane. But any leaks will not leak the two gasses at the same rate, which is why it is not a good idea to top off a blend. You should always reclaim and recharge instead. Then dispose of the reclaimed refrigerant properly.

Now, I don't see anything in the EPA regulations which prevent me from disposing of such a blend in my backyard gas grill. Perhaps there is something there though.

I get what you're saying, but all I'm saying is, you will never see ridiculous head pressures because you're using such a greatly reduced volume of propane (or whatever other hydrocarbon refrigerant) vs. how much 134a is required.

Comparing the temp/pressure curves of each material is fine and dandy, but it pretty much goes out the window here, because you're only using 10%-20% as much hydrocarbon material as you would 134a, in order to get the same cooling efficiency. This will more than outweigh any differences in temp/pressure properties between the two. Your analysis would be completely correct, if you were using like quantities of each material, but you're not. A 2 or 2.2 pound 134a system will actually function better with just a few ounces of hydrocarbon. You're never going to have enough volume in the system to create absurd pressures.

Richard Wooldridge · #80 08-05-2009, 04:06 PM

I've been using a mix of propane/butane in my '77 Jag for over 15 years now, and not a hint of trouble. Also, I've not had to recharge it since going to the mix. I used what I think is called GAZ, a french mixture for high altitude camping that has about the correct ratio. The vent outlet temps will get too cold, below freezing sometimes in 80 degree weather, but in the hotter temps (85 and above) it doesn't freeze. I just turn the unit off for a bit if it does freeze up. It does take considerably less gas to make it work properly, about 33% less gas. There is less gas in there than would be found in a can of hair spray, which many people have inside the cabin, a much worse scenario to me!

EricSilver · #81 08-05-2009, 04:13 PM

Quote:

Originally Posted by amosfella

It was doing 5C at the sensors in my 95 S320. It was 27C according to my outside temp sensor...
With R134a, the lowest reading I got after checking it with the same sensors was 10C.... It was only 20C outside that day...

Same engine, different car:

Recently recharged with R134a and in 90-degree weather can set the ACC wheel to 65, and within 10 minutes the blower spins down to near-nothing and the temp is effortlessly maintained.

I don't understand the aversion to R134, unless some efficiency is lost when doing the conversion from R12??

remotemark · #82 08-05-2009, 04:15 PM

Quote:

Originally Posted by EricSilver

Same engine, different car:

Recently recharged with R134a and in 90-degree weather can set the ACC wheel to 65, and within 10 minutes the blowers spins down to near-nothing and the temp is effortlessly maintained.

I don't understand the aversion to R134, unless some efficiency is lost when doing the conversion from R12??

Your car was designed to work on 134. The components designed to work with the higher pressure coolant. The R12 cars switched to 134 are still R12 cars in which the 134 does not adequately cool.

EricSilver · #83 08-05-2009, 04:17 PM

Quote:

Originally Posted by remotemark

Your car was designed to work on 134. The components designed to work with the higher pressure coolant. The R12 cars switched to 134 are still R12 cars in which the 134 does not adequately cool.

I see.

brewtoo · #84 08-07-2009, 12:04 PM

Quote:

Originally Posted by Richard Wooldridge

It does take considerably less gas to make it work properly, about 33% less gas.

Just curious. How do you know how much gas to put in?

Richard Wooldridge · #85 08-07-2009, 07:45 PM

I went by the results - ie, the temperatures and pressures. As soon as I got the temperatures I expected, I stopped charging. This resulted in roughly the same pressures as with R12. The most important temperature, to my way of thinking, is the temperature at the exit side of the evaporator. When it cools down, it means there is enough gas that it is still vaporizing at the outlet.. Any more charge won't accomplish anything.

mramay · #86 08-07-2009, 07:49 PM

What are the required pressures for R12? I have 35/275 and it's not cooling particularly well.

Thanks,
Mike
HOT Las Vegas

Richard Wooldridge · #87 08-07-2009, 09:08 PM

I suggest that you read this:
http://www.aircondition.com/tech/questions/82/

mramay · #88 08-07-2009, 10:06 PM

Quote:

Originally Posted by Richard Wooldridge

I suggest that you read this:
http://www.aircondition.com/tech/questions/82/

Very good answer! I'll keep my 35/275 and see if that will suffice in Vegas.

It's a little on the high side and the vents are putting out 55F vs the 40F I had before replacing a blown hose and putting in a new receiver/dryer, but it's "only" 93F today in Vegas. I'm now thinking that the 40F was due to lots of refrigerant, which resulted in some overpressure on the high side, which found/made a pinhole in the hose from the compressor.

airedale2 · #89 08-12-2009, 01:44 PM

Hello everyone,

havent posted for a while. I am using hydrocarbons in my ac on my 300d. Had to play around with the pressures for a while as the pressures from the supplier do not match up correctly. With trial and error i do have a functioning ac again. I am currently using products from envirosafe as it is a purified product. BBQ propane works fine, but the added butane keeps high side pressures lower. This is the reason for the blended product.

Tried lower pressures, and they were okay for cooler temps in the 80's. Tempuratures in TX are well into the 100's for most of the summer though. I have my low side pressure up to 55psi and my high side runs between 200-250psi depending on temps. Mostly around 225psi in 100 degree days.
I get about 50-55degrees at the vent while moving.

When running the motor at about 2500-3000 rpm, the pressures drop to about 35psi, which seems to be an ideal pressure when looking at r134, r12 and propane/butane. If you are charging your system with any refrigerant, you must run your motor at operating rpms. Most use 1500rpm as a rule of thumb, but remember that 617s like to routinely operate at 3000rpm. Then you get proper cooling across the outside condensor.

I have had the pressures up to 60psi with no appeciable losses or strain on the compressor. I have noticed that compressor runs with less strain than with the previous r134 conversion. The compressor was very noisy with r134, and not a good noise. It is now very quiet and smooth with hydrocarbons.

Hydrocarbons will work with ANY oil, mineral or pag. You do not need to flush anything unless you have an obstruction.

As far as conversions go, you only need to convert your r12 system with r134 fittings and then you can run any refrigerant you want. Epa has no standing on the use of hydrocarbons. Why, because the new refrigerant of the future 410a, is half hydrocarbons. And it runs at twice the operating pressures of its predecessor r22. If you are concerned with a leak, most leaks will occur outside the cabin in the high pressure side of the ac. If inside, it would be very, very minor and neglible.

So if i am correct, then it will be okay to use hydrocarbons in your house but not in a vehicle? Someone is going to make a lot of money off you naysayers. And thats okay. I just want to leave you my card when you call.

I am a fireman(that actually goes into actual burning buildings) and now i also have my ac certification soon to finish my assoc. in residential cooling. Looking from both ends of the spectrum, get used to hydrocarbons, because they are here to stay and will become the future.

By the way, r134 is on its way to being phased out along with r22. Then what are you going to use in your ac?

If anyone has any questions regarding charging their auto ac, feel free to contact me, i would be happy to help. Just remember, i assume no responsibility for what happens, including frostbite.

Matt L · #90 08-12-2009, 02:02 PM

Isn't R1234 now looking to be the next refrigerant after R134a? There were signs of R744 taking that stage, but it looks like 1234 is where we're going. Note that the ODP of both 744 and 1234 are zero, and they have very low GWPs as well (744 is 1, of course).

There is no retrofitting possible from 134a to either 744 or 1234, so I suspect that we'll be hearing a lot more about hydrocarbon retrofits for 134a systems in the not-too-distant future.