Don't get too excited, it's only a naked A/C compressor.

I rebuilt the A/c in my faithful old 300DT with new compressor, new factory hoses and receiver dryer. Flushed out the condenser and evaporator. I used, uh, test gas to fill and check for leaks with the intention of using R-12 after it all checked out. I found a leak at the compressor to mainfold flange and fixed it, losing seventy cents worth of propane as opposed to $75 worth of freon. For all the tree huggers.... I let the propane go into the atmosphere... so sue me.
Low side was too high at 65 PSI to please me so I replaced the expansion valve too. That was it. High side read 255 and low side read 32 PSI @ 2,000 RPM. Air temp at the center register was 43 degrees @ 70 MPH. My aux fan has a relay and it always runs when the compressor clutch is engaged.
A few days later noticed a bit of fog in the sight glass and checked again for leaks. None found so I added a bit more propane until it just went clear. Same pressure readings.
My mistake was that I usually jump the pressure switch leads on the dryer when I charge a system. It's keeps the compressor from cycling no matter where your CC settings are. This time I forgot to remove it.
Then I went on a test drive. One mile away the compressor blew it's cover off. Helluva loud noise like a big rig having a tire blowout. Just under four pounds of propane was released in less than two seconds
The charge must have gone completely under the car because the engine didn't stutter and the alternator brushes didn't light up the escaped propane
I attached a picture of the compressor. Anyone else ever see this kind of failure? Larry? Jim?
I replaced the compressor with a used one we had lying around and it works well so far. If I have no further problems with it, I MIGHT replace the propane with R-12 next year. Maybe not, but I will replace the compressor with a new one if I can't fix this one.
I'll follow up in either case.

__________________
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1984 300D
1985 300CD
1980 300SD
1993 SL500

That's pretty interesting - I'll bet it scared the heck out of you when it blew. Thank goodness there was no good ignition source close by. Interesting concept running straight propane. I did not realize it would cool that good. What kind of lubricant are you running?

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Jim

I run six ounces of mineral oil or capella wax free oil. Then it's only a matter of draining the propane and adding R-12.

Propane leaks are easily detected by the same electronic tester we use for R-12 & R134.

Scared me ?
I believe my sphincter tore a hole in my new leather seat.

I have seen this before.
That is a propane explosion inside the compressor.
Basically you created a micro diesel type compression explosion, in an area not capable of taking the stress.
A very good example of why you should never use propane or any flammable in an automotive A/C system.

If you are unlucky, next time the shock wave will travel into the evaporator and balloon rupture it.

There are several people killed every year using a flammable in an automotive A/C system.

If you want to check for leaks, use nitrogen or Co2.

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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
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You are way overcharged for HC refrigerant. Approx. 35% of R-12 recommended weight is what is generally used. You can figure it out from the molecular weight of the propane, iso-butane and compare it to the mole weight of R-12. I use ~ 18 ozs. of 70/30 propane/iso-butane as my "test" refrigerant in a 300SD (yours should be similar) that is rated for 2.9 lbs of R-12. Do NOT clear the sight glass or have too much. Four lbs of HC is a record

Here's some folks who have used HC. It's a discontinued board, but still worth reading.http://www.aircondition.com/wwwboard/alternative/

Here's another.. http://www.hc-tech.com/forum/pages/forum.html

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Yeah, propane makes a fine refridgerant. Pentane is (or was) used in -80C deep freezes for eons (they are two stage systems, R12 system used to remove the heat from the pentane system, two complete compressor/evaporator/condensor sets).

The only problem is when you have a small leak and get air in it by diffusion, which is exactly what I suspect happened to you. The propane/air mix will detonate when it reaches the O2 explosion limit in the compressor. You are lucky it didn't fail instantly, it would have blown the hood off.

Hydrocarbon AC charging is very dangerous, and illegal in most states for the exact reason you just demostrated -- explosions and fires.

At this point, I would flush the system and "new" compressor and recharge with R134a. You don't loose that much cooling capacity, and it's at least safe.

Replace all the o-rings, charge to 50 psi with either 134a gas or CO2 (or helium on argon/CO2 mix) and test for leaks. If it won't hold that pressure indefinitely or hold 29" vac for more than 30 min, it still leaks, fix it.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I called my buddy in New Zealand since it was he who told me about using propane in the first place. Three or four years ago his words were "just charge it up normally and leak test, that's all we use here. Not quite as cold as R-12 but servicable."

What he didn't say at the time was NOT to use the view window (sight glass to us) and rely only on your gauge readings. His shop services late model GM trucks and he just told me that he hadn't seen a view window on anything he worked on in about 20 years.

You were spot on fellows. Major overcharge. My high side now reads 165 to 175 @2,000 RPM and the low sides reads 30 to 32. Oddly enough the air temperature at the center vent reads 54 degrees at 70 MPH with OAT @92. That's eleven degrees hotter than the 43 degrees I got when overcharged.

And for the record. I was edgy about even mentioning my propane use for A/C. I would never recommend anyone else using it, but I use it. I guess I do many things that I wouldn't recommend others doing. I did find that by charging a freshly rebuilt system with propane, it was easier to find a leak than it was when using dry nitrogen. My buddy in New Zealand said he used a BIC lighter to check for leaks he couldn't hear. He just blows out the small blue flame and tightens the fitting

I learned automotive A/c in 1965, hold current ASE Master certs and a 609. That just means that I SHOULD know what I'm doing, even when I don't. I must have overcharged 30 or 40 systems in the past three years without a mishap. Lucky, and I know it. I normally charge the rebuilt system, test for leaks, test drive to get register temps, and then leave it overnight. Leak test again and refill with R-12. Test register temps again (always colder with R-12) and ship it. No leaks means no comebacks.

I was able to press the cover back on the compressor using a press and a couple of C-clamps. If it holds a vacuum overnight I'll pressure test it with nitrogen tomorrow. I doubt that I will change it out until next summer.

BTW, this is my car that we are discussing and not a client's or a friend's car.
I'd hate to try to explain to a client why his car looks like someone dropped a cherry bomb in a beer can

The amount of information that comes from this forum's members never ceases to amaze me. Thanks again.

I don't think it exploded, I think the head pressure went waaaaaayyyyy too high and just blew the thing apart. Straight propane is not a suitable substitute for R-12; the vapor pressure is too high, the pressure/temperature curve is too different. There used to be plenty of discussion on this topic on the alternative refrigerants board over at aircondition.com. Unfortunately, the alternative discussion has gone away; even the archives are missing.

Here's two web links to discussions of using hydrocarbons in automotive refrigeration systems: http://yarchive.net/ac/expansion_valve.html and http://yarchive.net/ac/hydrocarbon_recipes.html You need to blend the propane with isobutane to lower the overall vapor pressure.

I don't think it exploded because hydrocarbons are only flammable within a narrow range or hydrocarbon/air ratios. Think of the jets on your backyard BBQ grill. If it's setup for propane, you cannot hook it up to natural gas and have it work. If it lights at all, it'll barely produce any heat. It's necessary to mix the two components in the right ratio to get them to burn. I seriously doubt if that happened inside your a/c system. If it had enough air to explode, it wouldn't be cooling at all due to the non-condensibles in the system.

My $.03 (wordy post with assigned reading)

- JimY

Jim,

See my previous post for link to the alternative refrigerants archives. Seven loooong pages of 'em.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)