I'm a newbie to the forum.... but I was curious on who is running 12A refrigerant in their AC units....If you care to tell the pros and cons about what you experienced or what you've seen using it?I'm probably like alot of bus owners. I bought a MCI bus 1985 96a3 four years ago which has been a bigger project than I first anticipated but I'm a mechanical person and enjoy learning....I've learned a lot about buses! It would be easier to tell you what worked on this bus then didn't.
If you have any additional information like superheat and sub cooling calculations how much was weighed in and what you found on the high-pressure side for a reading(liquid side)
12a is Flammable and illegal in the US. I would avoid it. Are you sure your bus is setup for R12? Most of what I have seen is setup for R22. My 1981 was R22 and I retrofitted 407c, it is super easy and very safe.
Yes sir I know it's flammable.... it's in my new refrigerator and my new window air conditioner.....Just checking
If you have r12 I think you can pretty safely go to 134a with just an oil change. All of the bus system uses flare fittings and the compressor is used with both refrigerants interchangeably. But be sure you have R12, the bus systems have TXVs so if you put 134a in a R22 system it will do weird things. These bus systems are more like a commercial HVAC then automotive.
I filled by weight, I have not had a chance to check the subcooling (I just got a testo smart meter kit a few days ago)
I wrote about it in another thread, Basically you need 68 weight POE oil, drain the compressor and fill with the POE. Its okay if a little mineral oil is still in the system. Then vac down and make sure you hold vac for 24 hours. There is a lot of surface area in the system. It took me two cycles of 1 hr with the vac pump to stay at -29inhg, fill with 24 lbs of 407c.
Yes sir, I have Elitech gauge/ computer my system was running or 134A.... Yes sir I know the buses run a TXV not a fixed orifice thanks for your input
I actually pulled vacuum for about six-eight hours and then filled it with 100 psi of nitrogen and let it sit overnight (psi was still 100)and then pulled vacuum again before I weighed it in....It also makes it easier to pull vacuum porn from the high side and low side with the shut off valve disabled With a magnet
Quote from: Chuckyducky on August 03, 2020, 05:46:08 PM
Yes sir I know it's flammable.... it's in my new refrigerator and my new window air conditioner.....Just checking
Stationary appliances have very little in them and generally are safe as the whole system is contained and not moving. Your putting 24 lbs in a bus.
Your bus system is running 134a now? What compressor do you have?
I would stick with 134A if you have it.
HC12a is going to be hard to find and its pretty expensive. $20+ for 6 Oz on ebay. ($10k to fill your bus)
Is it safe to assume you have some HVAC experience? If you know what your doing I would change out the TXVs and use R410a if you have the big compressor.
Yes sir I recovered the 12 a and no longer using it just trying it for an experiment....😁 I recovered 32 pounds of 134a Weighted in 13# of 12a and I can tell you 12a outperformed 134A hands down it's too bad it's illegal and I had to pull it out! My compressor is an 05G Oh by the way the 12 a high-pressure side was 60 pounds less on the high side then 134A running on a 90° Day high humidity with a vent temperature of 36° and or 134A was around 50° vent temperature
Just so we're clear r134A burns also Along with your fuel injected cars running 60 # of fuel pressure with 20 gallons of Gasoline.... And 150 gallons of diesel fuel mounted under your seat on your bus And who knows how many propane tanks people are carrying around!
When I bought this bus The air conditioner malfunction light stayed on because the jack @$# Who just put the new 05G pump on Didn't set the unloaders correctly in the filter dryer was clogged And I had to use acid on the condenser door it was so clogged
Quote from: jap42 on August 03, 2020, 06:11:49 PM
Stationary appliances have very little in them and generally are safe as the whole system is contained and not moving. Your putting 24 lbs in a bus.
Your bus system is running 134a now? What compressor do you have?
I would stick with 134A if you have it.
HC12a is going to be hard to find and its pretty expensive. $20+ for 6 Oz on ebay. ($10k to fill your bus)
Is it safe to assume you have some HVAC experience? If you know what your doing I would change out the TXVs and use R410a if you have the big compressor.
Yes sir,what would be the pros and cons of using R410a refrigerant in a bus air conditioner ,what kind of pressure would I likely be seen on the liquid line? I'm looking for a low maintenance /low pressure AC system that I don't have to work on every season..... That cools extremely well.
I also have three 1982 Copeland K body Electric compressors that didn't work due to broken valve plates and a stuck rotor that I managed to save that are running r12 (Freon) now..... Experimented with three different gases in the one unit that had a stuck rotor and I settled on r12 only because The refrigerant in a K body the Freon is in contact with the motor windings.
Both of my Copeland compressors on the Custom Coach built house a/c units are running r12 on my bus. They were topped off a few years ago with some "universal" refrigerant by a commercial refrigeration tech. Since then I've acquired a 30-pound can of r12 for next time around when things need work.
The main bus system can from GM with r22 in it, but when the new compressor was installed two years ago we went with r438a (M099) which seems to be doing just fine keeping the bus cool.
A lot of people make the argument that there are other flamables on the bus. A few notes to remember:
Diesel has an extreamly high flash point. Try dropping a match into a bowl of diesel.
Gasoline in a car has a simular issue except it does evaporate at outdoor temps and the vapor is ignitable. In you car a very small volume is under pressure and in a liquid state, which will leak out a liquid.
A fire from the gas or diesel in a vehicle will start and burn slowly and give you time to evacuate
Propane is held as a liquid in a heavy walled pressure vessel, its distributed at very low pressure and has very limited flow. About 70 CFM with a 175k btu regulator. In a bus you would need about 180CF in the bus to combust. So about 2.5 minuets if a 3/4 propane line ruptured. Propane has a bitterant and odor additives. at 70CFM you would smell it in seconds and have time to vent and shut off the gas.
Refrigerant is pumped from the back of the bus to the front in a liquid form around 200PSI through a 3/4" hose. If that line ruptured it could drain all 29 Lbs in seconds. That 250 cubic feet. There is very little odor to refrigerant.
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The HC12 does preform well but is a huge safety issue. Expensive and hard to find. Not sold in stores.
134a is an easy drop in. Its Cheap and available everywhere without epa certs.
R12 would work well but its getting expensive and hard to find. You would need an EPA card to buy.
R410a preforms very well, is cheap, and easy to find. You need an EPA card and you have to change the txv.
R410a runs much higher pressure so the whole system needs to be able to handle that. I would probably not realistically go this route.
If your system is made for 134a your going to get the best performance from it.
R12 and HC12 are going to run higher pressure and therefore require more power to compress.
Your HC12 experiment worked because you under charged. Your ambient temperature will make a huge difference in that performance. It sounds like the previous owner may have messed the whole install up. I think its still suppose to be 29 lbs. and with the unloaders not set very little would be pumping
Superheat can be a very good indicator of how much refrigerant is in the evaporator coil of an air conditioner......hc-12 with 13# in a bus most likely is not under charged..... That's why you check the superheat or sub cooling...... Knowing how full the evaporator is when charging is your friend!
But, on the DL you have an accumulator with two sight glasses, one at the top and one at the bottom and that thing must hold about a gallon of liquid refrigerant. How many pounds do you suppose that is, 7 or 8?
So isn't it reasonable to expect that the refrigerant level should always be between those two sight glasses? It seems to me that as long as you always have the bottom one covered you're golden. Pretty simple and easy. (If your hinges haven't sagged :'( )
Jim
Back in the days before we ran Prevost we had a fleet of MC-9's; 6V's, 8V's, 71's, 92's. Had both 5F30 and O5G compressors. In upgrading the refrigerants we settled on Freeze 12 as our replacement refrigerant. The performance was much better than R134A, at the same price point. This was especially true with the 5F30 compressor. With MC-8's and 9's which have small condensers the condenser core must be kept clean and be in good condition or you are pissing in the wind. Keeping the cabin comfortable in 100+ temps with 47 souls on board is a chore and expensive and the best you achieve is around 20-25 degrees cooler than ambient. We were big believers in Freeze 12. I think it is still available, this was 20 years ago.
Sight gauges on the receiver tank are a good reference.... As long as the TXV stays flooded in all ambient temperatures And when you're done pumping down the system to see if the receiver holds the charge.... A clear sight is not always 100% encase you have a bad TXV you'll never have a clear sight until it slugs the compressor
It's still available I have about 60 pounds of it in my shop.... I've been using it in old cars for 20 years.... Just make sure you tag it....