DaleClark

iTrader: (55)

Few things -

The '93-94 RX-7's use R12, the '95s use R-134a. From what I've heard, the '95s didn't have the coldest AC - it's better than a 134a conversion, but still not as cold as the '93-94s. That's part of the reason I bought a '94 and not a '95 .

The air-powered vacuum pump from Harbor Freight is CRAP. I bought one some time back - first off it's JET PLANE loud, and second it can't pull a full, deep vacuuum - it doesn't get down low enough to properly pull all the moisture out of the system. It's a waste of money. You'd be better off spending a few bucks on a used vacumm pump off Ebay, especially a quality brand like Robinair. Or, just have a shop do it for you - again, I had a full vacuum and R-12 charge for $120 - you just can't beat that.

I think it's already been well said, but I would NEVER run propane in an AC system. One of the things you can likely get away with, but if you *do* have a problem, it could be your car or your life. Not a gamble I'm gonna take to be a cheapskate - I'd wait a bit and save my money, then do it right.

Dale

DamonB

I have always used an air compressor to pull the vac. Remove the inlet filter from the compressor and then rig some fittings to connect that to the a/c. Works like a charm and many people have big air compressors.

I replaced all the seals and converted my car to 134a a couple years back. It does fine until it gets really hot (which is often in Texas) and then it takes a while to cool the car if it's been parked in the sun. My original 130,000 miles a/c compressor is also a little tired so I have a new compressor waiting to go on. Once I leak check it and pull a vac I'm going to recharge it with R12. I plan to replace the expansion valve for the hell of it to be certain everything is ready to go.

tzbfwt

iTrader: (1)

Dale - thanks for the tip on the vacuum pump - did you have a set a gages hooked up when you were using it? What kind of vacuum did it pull? 10 inches? I think my gages go to 30 inches of vacuum- and I'm sure a good Robinair would pull that - but if the HF jet engine will pull 10 inches - that would be good enough for me... I figured it was an orifice based pump - so you need a healty air compressor to power it - what size did you use? I watched a friend use one - but he had a 230V compressor - a big one - 10SCFM big at least. He didn't have gages - so don't know what it pulled. I've also heard that you can salvage an old compressor out of a frig and use it as a vacuum pump. and you should change your filter/dryer if the system has been open for a while - before you charge it.

Now - DONT USE PROPANE DONT USE PROPANE DONT USE PROPANE

there I've said it three times - but you guys better never go to Canada (they run propane power Silverados all over the place. Pressure? Try 3000 PSIG tanks in/under the bed. for that matter - stay out of most big warehouses too - propane powered fork lifts...

as far as the post above about the refrigeration gas under going some chemical change at the expansion valve?? wow - I hope you don't have an engineering degree if you believe that one... all refrigeration cycles I ever learned about involved a gas that boils at room temp and can be compressed to a liquid under a few hundred PSIG - I think a good R12 system runs at about 250 PSIG. when the liquid vaporizes in the evaporator, it absorbs heat, then it gets compressed again - runs thru the condensor to reject the heat, then back to the evaporator/expansion valve. Simple - R12 and propane just happen to have about the same boiling point - so they both work. If it were my car - I'd probably do a fill with propane to check out the system - if it stayed charged, I'd vacuum and refill with R134A.

Geesh guys - propane is not the Devil, I'd be much more concerned with those fuel and oil lines right above my cherry red turbos - didn't Broken 93 just catch his on fire with an oil line leak?

DaleClark

iTrader: (55)

The Harbor Freight vacuum pump pulled about 20" of vacuum. You really need to get a hard vacuum, closer to 25-28". The reason is water will boil in a vacuum - that's how you get the moisture out of the system, it boils and comes out as a gas. With a lower vacuum, the boiling point of water is higher, so there's no guarantee you can get ALL the water out of the system, which is essential.

Dale

BlueRex

Dale, the price of R12 varies by region. I've been quoted at about ~$70 a pound over here in CA. Since the production was halted at the end of 1995 the prices are only going to go up which is why the conversion kits are so popular. Any idea how many pounds are required to fill the a/c system?

Any comment on my previous question about the lack of performance from r134a in an r12 system being related to the compressor design?

DamonB

It's a combination of things. In a nutshell 134a is less efficient so cars designed for it have larger evaporators and condensors. A car originally designed to use R12 has evaporators and condensors that are not optimized (too small) for 134a and thus the a/c becomes "handicapped" when you convert an R12 system to 134a.

The other big bug-a-boo is that 134a runs hotter. If you merely charge an R12 system with the same amount of 134a your pressures will end up too high and the compressor life will be drastically shortened. You have to use less 134a to keep the system pressures in check. In the end it's a double whammy: The 134a is less efficient and you have to use less of it. I never charge the a/c without a manifold gauge set so I can monitor the system and be sure everything is within safe parameters.

dgeesaman

iTrader: (7)

There is a huge difference between systems designed for propane, and putting propane in an AC system. Propane fuel tanks are designed in many cases to withstand an 80mph crash into a solid concrete wall. Yes, we have flammable fuel lines in our cars too, but they are away from heat, crumple zones, and other nasties. IIRC the A/C lines are all over, and they're aluminum.

Dave

BlueRex

Thanks for the info DamonB.

In you previous post you said that you converted your car to r134a. Any idea how the conversion kit helps opposed to just putting r134a in an r12 system? IIRC all I saw in one of those kits were some new fittings and r134a refrigerant.

DaleClark

iTrader: (55)

The car only needs like a pound and a half of freon, BTW. It will be more or less depending on the region, but it should still be reasonable.

The proper way to do a 134a conversion is a little time consuming. The oil in the system should be drained and replaced with 134a compatible oil, and the O-rings should be replaced with 134a compatible O-rings. The system then needs a hard vacuum and a proper charge of 134a - Damon's right, you have to run less pressure with 134a to keep the head pressure at the compressor in check.

134a works great in a system it was designed for. It would be nice if there was a way to run 134a and have the same cooling you get with R12. For some people up north, 134a might be just fine. For Florida's heat and humidity, it isn't doing the job - car takes longer to get cool, and you end up running the system on full-blast more of the time.

I can't stress enough how pleased I've been with the AC in my car - not only does it blow ice cold, but it makes little to no difference in how the car runs, unlike my old FC 'vert that felt like I tossed out an anchor with the AC on.

Dale

mad_7tist

there is no such thing as an r-134 o-ring. when you retrofit replace the ones you remove and any that were leaking.

DaleClark

iTrader: (55)

They did change the material the O-rings are made of to be compatible with 134a and the newer compressor oil. But, if you buy any new O-rings, you'll most likely only be able to get the 134a-compatible-material O-rings.

That said, if an O-ring is still working, it will probably keep working with 134a. But, IMHO it's a good idea to take care of ALL the O-rings if you're doing some major AC system work, as they're a very frequent failure point.

Dale

DamonB

There are in fact different o-rings for 134a systems but it's not because of the freon, it's because of the oil. R12 and R134a systems use different oils and R12 oil is not compatible with 134a oil. When I converted my system I did exactly as DaleClark describes. I removed all the old freon and also drained the drier and the compressor of their oil. I replaced every o-ring in the system with a new one that is compatible with the new 134a oil. R12 oil becomes acidic in the presence of 134a and its oil so then it eats your o-rings and compressor seals over time. Again this happens over time and combined with people over charging with 134a leads to the "I converted and it worked great for a while and then crapped out" stories.

There are two types of oil IIRC correctly: ester and PAG oil. I forget which goes with which system but my understanding from the great a/c shop I found was that you could run r12 oil with r134a seals but you couldn't run r134a oil with r12 seals as it would eat them. The new o-rings I installed for the r134a conversion happen to be green rather than black. I don't know if that's a way of telling them apart or not.

The "conversion kit" I used was nothing more than the commonly available adapters for the high and low side ports. On top of that I drained all the oil from the system (it sits in the compressor and drier when the system if off), replaced ALL the o-rings with 134a types, pulled a vac to check for leaks and then added the r134a oil. I then pulled another vac and charged the system. My 130,000+ mile compressor is wearing out because even when charged correctly the high side reads a little low and the low side reads a little high. The seals are wearing so its pumping efficiency is going down. I got a steal on a new compressor long ago but haven't added it yet. I'll do that soon and switch back to r12 most likely.

mad_7tist

you are right about the oil. it does turn into black goo when it is exposed to moisture/air for any length of time. i think it is crazy to tell people they need to change the o-rings because the refrigerant is different. they are 10 years old so do it.. ok maybe. if you flush out the condensor and evap. replace the drier (all of which should get done) you need to put new orings on those components. an overwhelming percentage of ac problems are component failures. on r12 systems the schraders leak. and on cars that have them the crimped flexable lines they fail. o-ring problems are usually installer error wrong o-ring it was pinched etc.
damon have you give any thought to your expansion valve not functiong properly? ester is the old stuff pag is new. the ase says that the incompatibilty of the 2 is that mineral oil will not move through the system with 134 well enough to keep the pump properly lubricated.

Speed of light

iTrader: (8)

Guys, There is a lot of misinformation and half-truths contained in this thread. So I'm going to chime in here on with factual information on a few of the points, drawing from my engineering design experience with refrigeration systems.

Probably the best thing to do IMO (for most of you), if the $$ is reasonable, is to recharge your R12 system with R12. Most of the shops doing this use refrigerant that has been recovered from other systems. There are alternative refrigerants of several different types that also could be used with good results, but some research must be done to insure materials compatibility with the a/c system. (With the exception of HC12a, which is a drop-in and will work fine in any system--period.)

I would, under no circumstances, convert to R134a. It is a very poor refrigerant (relatively speaking) and doesn't do anything very well. R134a exists as a political solution to appease the companies that produced the problematic R12, which formerly made them very wealthy.

1) Mineral oil used in R12 systems is not miscible with R134a and MUST be changed to a POE or PAG type oil, which are not very good lubricants and are very hygroscopic. Ignoring this point will result in compressor failure;

2) R134a is a much smaller molecule than R12 and requires system changes, such as barrier hoses to prevent it from leaking out. It will find all the leaks you never thought you had in an R12 system;

3) R134a is very flammable--even more so than propane--and produces toxic products when combusted. You guys that are concerned about propane should check out the ignition temperatures and the LEL's for R134. How R134a was classified as non-combustible took an act of Congress--literally;

4) R134a is considerably less efficient than R12: has poor pull down performance, and operates with higher head pressures (another potential compressor failure point and larger power drain on engine).

Sorry, R134a is just a lousy refrigerant for a lot of reasons.

Additionally, pure propane is not recommended, as it is not well matched to the R12 refrigeration cycle; however, a good HC substitute is 50% R290 (propane) and 50% R600 (isobutane), aka HC12a or equivalant. Its enthalpy characteristics are very close to R12, it has a large molecule, no materials or oil compatibility problems, it's more efficient, it's cheap and easy to use.

BEFORE recharging the system with any refrigerant, I cannot overstress the importance of getting all of the air and moisture out of the a/c system. In order to do that effectively, you need a high vacuum. At room temperature that means at least 29.25" of Hg to flash out all of the moisture. Anything less will really not get the job done. A 28" vacuum, for example, will only remove 94% of the air. Air cannot be condensed in an A/C system and will get trapped at the top of the condensor resulting in loss of efficiency and higher than normal compressor discharge pressures.

Hope this helps....

tzbfwt

iTrader: (1)

So Dave

how safe do you feel with R134A in your system now??

thanks Speed of Light - very informative Post , but where the heck do I get my hands on some H12a?

any truth to the rumor that R12 was phased out because Dupont's patent rights ran out and it had to come up with some new gas to patent?