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Old 09-10-2020, 07:53 PM   #1
billr
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Default Propane for A/C

I hope to get some useful discussion, but expect to get some blasts, too. I will try to keep "thick skinned"!

I have read other hints here that R-290 (propane) can work well in place of R-134a; but is illegal here in USA due to fire danger. Being a curious soul, I wanted to try anyway...

It is a '95 SL2 and the A/C has not worked for many years. No known damage, but just stopped cooling and it isn't my primary SL2 so I figured to never bother fixing the A/C. Nothing to lose, right?

I connected the gauges, no pressure in system, so I pulled a vacuum and it held fairly well. So, I charged it with barbeque propane; left the PAG oil in there.

Cooling does definitely seem good. I can get 20-30F at the dash outlets. The low-side line into the compressor has frost on it, even with hot air from the radiator blowing on one side of that line and the exhaust manifold about 6" away on the other side. Pressures are different, of course. I settled on 300-350 psi high with the low staying fairly constant at 20 psi. I tried varying the charge a lot, going up high enough that the compressor was cycling on/off from the high switch (about 400-450 psi); that 300-350 seems to be best so far. With propane, I had no qualms about adding/bleeding to try a lot of different pressures.

So, I'm trying to decide now if I should go ahead and flush all the PAG and replace with something that is compatible with propane and R-134a (POE?) and recharge with real R-290. I don't really need working A/C in this car, but would sure like to prove out a replacement for R-134a; especially since it seem to cool so much better!

PS: I figure the charge I have in there is about equivalent to 1 qt of gasoline, and would have to get "trapped" just right, if released, to keep in the 2-10% flammabilty range to burn at all. I'm not too concerned about the fire dange
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Old 09-10-2020, 11:23 PM   #2
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Default Re: Propane for A/C

This is available in Canada.
https://www.redtekstore.com/
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Old 09-10-2020, 11:40 PM   #3
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Default Re: Propane for A/C

The supplier for that link is in TN.
Here is some info from the supplier
https://redtek.ca/refrigerants/12a/
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Old 09-11-2020, 12:02 AM   #4
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Default Re: Propane for A/C

You like many assume no damage to vehicle ac systems. If no damage occurred then it should work. Like many unfamiliar with pressurized systems (aerosol spray cans of paint, shaving cream, Reddi-wip cream, Pam, brake and throttle cleaner, propane tanks for BBQ or portable torch, each system is designed for a purpose and safety for public use. With propane, every steel cylinder is designed for rigorous safety against dropping onto a concrete floor from a certain height without breaking off its valve as well as expected extreme temperatures when stored out in sunlight. There are zero vehicle ac systems using steel or copper tubing for lines, condenser coil, evap coil and drier. In my limited knowledge, every vehicle ac system uses aluminum, pressure rated hoses and fittings to meet engineering standards and safety margins with whatever refrigeration gases are determined for safe use. Your car is now a bomb waiting for the right circumstances to explode (worse case scenario already proven) to best case with a rupture ignited with an ignition source to burn as a torch until all pressure is released. You can search for the explosion of a so called research experiment going badly when propane was deliberately released in a car with windows up and deliberately ignited by someone attempting to prove propane isn't flammable. Remember, you assume all risks when an accident occurs even if not your fault but propane is released either by rupture or damage to release it as if opening a propane torch without lighting it. All it needs is an ignition source whether under the hood or inside the car when a spark occurs from switch or wire break. Remember, you measured between 300-350 psi on the high side. This pressure remains high as long as ac is running. Pressure drops down to whatever lower pressure is seen but won't be below 50 psi. To state no damage occurred is wrong.

98% of vehicle ac damage is about the leak no one wants to admit to but will run to the store for the refill kit to refill a..........leaking system. Your system simply leaked out, period. If physical damage occurred, you'd already notice it as any catastrophic damage to ac systems usually results in an immediate release of pressurized refrigerant, oil and dye. Oil and dye leave their tell tale signs with dye showing up as green and glows with a uv light since it's fluorescent dye. If you do not use an inexpensive uv light to search for dye marking the leak area(s), two likely leak sites are the two service valves. Both should exhibit traces of refrigerant oil and dye as dye remains permanently in solution in a system. Once released, dye will remain detectable for a few weeks but fade over time. Service valves (when a system is open for repairs) are the easiest parts to replace before evacuation procedures. While service valves are the main shut offs, the caps are considered the main seal against valve leaks. GM considers trace leaks as less than an ounce per year. 28.35 grams per ounce. A loose or worn cap missing its O-ring simply allows refrigerant to leak.

Canada does not forbid using r12a, known with several names as H12a, frosty cool, duracool. It's forbidden here in the USA. Its a mix of propane and butane. There's a very old video of a car meet from one of the mvac sites telling the story of a '60s/'70s Jaguar using duracool. Apparently the owner replaced one of the high pressure hoses as this hose was a little longer than the original. As he drove into the grass parking area to meet up with friends, as soon as he stopped, he was told a fire was coming from under the hood. Yelling and screaming ensued until the fire was put out. Severe hood damage. The longer hose was tie wrapped but they broke and the radiator fan chewed into the hose until it ruptured, releasing high pressure flammable refrigerant. No one died but the car was damaged. He assumed it was safe to use duracool instead of expensive r12. Older cars used distributors and one source of ignition. To say the least, the car lost value after the incident. Two examples I found over the years of using substitute flammable refrigerant. Yes, only two. Nobody likes admitting mistakes and owns up to it so there may be others but that's speculating. MVAC pros share horror stories amongst the group. I found the mvac sites and discovered the two incidents.

In my opinion, it's far easier to buy and use an inexpensive uv light to find dye markers from a leaking system than assume zero damage occurred. If zero dye or refrigerant oil isn't found after extensive examination, the evap coil is always presumed leak free since it is buried safely in the middle of the interior directly behind the firewall. If a leak occurred, it would be the two fittings to the thermal expansion valve O-rings. Again, dye marks where refrigerant leaks out under pressure. If this system was originally r12 then a 1/4 oz of dye added into the system is more than enough for future leak detection.

I've repaired r12 systems over the years. None use dye. R134a systems under GM configuration use dye as the easiest and simplest way to find leaks with many unfamiliar with refrigeration repairs. I am not an expert nor a professional. Just a diyer with some knowledge willing to pass on info since its saved me money on home repairs equal to ac repair shops. My first r134a repair was to my L300 after 10 yrs of reliable service in the streets of NYC (potholes galore). Found the leak within 5 minutes with a uv light after parking at Home Depot at dusk where dye glows easily. Three years since the last repair with one of two worn out fans and the second one having one poor electrical connection, burning the plastic connector. Bent the male pin to fit better and erratic ac cooling went away (one of two fans not running lowers cooling).

Personally, my guess (sight unseen) is if you determine zero dye and oil leaks then the two service valves should be replaced. Evacuate the system and refill with r134a. If this system was converted from r12 by adding screw on r134a adapters, then its your choice to flush the system, replace all O-rings with r13a compatible rings, replace the drier and pour in pag oil, The original r12 to r134a modification was screwing on r134a fittings and pouring in about an ounce or more of ester oil to allow r12 mineral oil to mix with ester oil. R12 mineral oil isn't compatible with r134a. Ester oil bridges the incompatibility issue without having to flush a system ($$$ when repair shops are involved). If your ac system is r134a from the factory then flushing isn't needed as pag oil is already in the system.
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Old 09-11-2020, 12:20 AM   #5
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Default Re: Propane for A/C

Just wanted to note that the REDTEK 12a product is actually R290 according to the safety data sheet.
Here are some equivalent weight charts that you might find helpful.
http://63.135.115.175/techinfo_char_wt_charts.html
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Old 09-11-2020, 11:39 AM   #6
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Default Re: Propane for A/C

Yeah, I also saw that in the MSDS. I think I am going to remove the propane and back-fill with a small amount of R134a while I regroup and decide what I want to do next.
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Old 09-11-2020, 01:19 PM   #7
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Default Re: Propane for A/C

I ran it again briefly this morning, got 17F at the center dash outlet. I removed (to full vacuum) the propane, got about .657 lbs of propane out
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Old 09-11-2020, 03:45 PM   #8
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Default Re: Propane for A/C

Billr, what are you using to measure vent temps of 17 degrees F?
Digital/laser type or kitchen/pocket circular/mechanical immersion probe?
If an immersion type, then, have you calibrated it recently (spin the nut under the head and set after immersing in boiling water and then ice water)?
And now I still don't believe that an immersion type will read AIR accurately. I know cheese makers that use this type will only test when they plunge it into liquid, if they use this thing to measure air, it would result in a messed up batch of cheese because this is not accurate in the air, only in liquid.

Do you have some other gauge designed for accurate AIR temp measurements?
And, what was the ambient temp and humidity at this reading?

The AC system is limited on low side temp by the thermo-switch that (I believe) turns the system off at 34 degrees F.

Given less than perfect heat transfer to the air (like measured 3 inches from the vent grille) about 40 degrees at the vents is usually the best it gets.
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Old 09-11-2020, 05:06 PM   #9
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Default Re: Propane for A/C

Using a fine-wire type K thermocouple and Fluke 51 meter. Ambient was about 75F with humidity 45%. I check the TC/meter combo once in a while in boiling water and ice water; I believe it is within 1F of true.

Remember, I had frost on the low-side line going into the compressor yesterday when everything else was hot. Best dash temp yesterday, when all was hot, was in the mid-20F range, but I saw 18F early on, before the engine/manifold/radiator temps came up.

Next step is to choose a flushing fluid and method to get out the PAG. I have acetone, hexane, ethanol, isopropanol, ethyl acetate, and toluene readily available; any guesses as to which will work best on flushing PAG?
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Old 09-11-2020, 06:38 PM   #10
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Default Re: Propane for A/C

May I ask why you're flushing the system if its already using pag oil? Are you aware that pag oil is the preferred lubricant for r134a? If you're flushing to replace it, fine. Examine it for traces of aluminum chips or other metals. A crude at home oil analysis can tell you many things by feeling a sample between fingers. Pag oil is light honey colored and tinted from GM dye if this is the original r134a system. Search around for solvent compatible for flushing r134a systems, leaving little to zero residue that can contaminate a system. Any petroleum solvent will leave residue in a system to contaminate it.

With evap/outlet temps around 18F, the possibility of freezing condensation is assured to create a block of ice over the entire evap coil surface. I'm surprised the thermal expansion valve allowed temps to go below freezing. A guess is propane fooled the txv by virtue of its chemical characteristics different from r134a. All refrigerators using r134a don't use txvs. Ice making/subfreezing temps are accomplished with calibrated capillary tubing.
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Old 09-11-2020, 06:39 PM   #11
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Default Re: Propane for A/C

Nice testing setup!
I have never used this stuff, but it seems to be right in line with all the other flammable solvents you listed....(just don't smoke while you work!!)

https://supercool.ac/product/ac-flash-flush-quart/
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Old 09-11-2020, 08:20 PM   #12
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Default Re: Propane for A/C

"May I ask why you're flushing the system if its already using pag oil? Are you aware that pag oil is the preferred lubricant for r134a?"

Was I that unclear about what I am striving for? I don't want to use R-134a; I want to use R-290 (propane). My understanding is that PAG is not the correct lube to use with R-290.

My apologies for posting this here, it probably should have been in the "S-series Mods" forum.
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Old 09-15-2020, 10:00 PM   #13
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Default Re: Propane for A/C

I've used Freeze 12 with good results. You could also reduce the propane pressure. When the evaporator frosts, that restricts airflow. The excessive pressure also uses excessive fuel. You just want to get the vent down to 40 on recirculate. That's enough. Mine get to 48, and that's plenty for me. Fill until you get between 40 and 45 degrees. Then stop. No more is needed.
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Old 09-15-2020, 10:33 PM   #14
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Default Re: Propane for A/C

Yes, when I get back to it I plan to do exactly as you say. That will reduce the high/low differential and reduce the charge of "deadly" propane in it. I may even charge it once then remove the charge to determine how many lbs, then recharge. Propane is cheap and easy to work with...

And, of course, it will reduce chance of loading the evaporator with ice. I got a kick out of that concern; who ever has a big problem getting A/C to not cool too much?
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Old 09-16-2020, 12:03 AM   #15
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Default Re: Propane for A/C

As I've always only ever topped off my system, I've always been cautious with how much I add. Should I ever evacuate the system, I could put the correct amount in by weight. That said, I've always tended to lean on the warm side of things. This summer I was bold, and charged the system well over 200 psi with a consenser temp of 120, and got the inside down to 48. This year was also the first year I used a thermometer on the condenser. There are many charts that specify ambient temp, but few if any that state actual condenser temp, which can be obtained by spearing the thermometer into the cooling vanes of the condenser coil. The condenser temp more directly relates to condenser pressure than ambient temp, so I don't know why more don't specify a chart for that. At any rate, I'd like to get the interior as cold as necessary without putting excessive pressures on a 22 year old system, so roughly 250 psi with 110 degrees on the condenser and 48 on the vent in recirculate seemed adequate to me.
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Old 10-01-2020, 02:21 PM   #16
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Default Re: Propane for A/C

Propane is back in there. I settled on 25L/245H (psi), which seemed to yield 25-35F at the dash vent. Actually, that is a thermocouple stuffed well down into the duct going up to the dash; so dash temp is probably higher. Regardless, my wife will like it, but it is uncomfortably too cold for me.



It probably is still too much charge, as that T/C dropped down to a steady 22F when I drove around a bit at 40 mph. Tomorrow I will take it for a longer ride, and at highway (75 mph) speeds for a while. Stay tuned!
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