Improving the AC system's efficiency
 

It is a well known fact that running the AC system can drastically reduce gas mileage, so I did what I could when I replaced my AC compressor last year to improve its efficiency, and therefore reducing the amount of power it wastes while also improving performance.

The first thing I did was I tuned up the system the best I could. I removed and flushed the evaporator as well as all of the AC lines, I replaced all of the seals as well as the TXV and the filter dryer, and I insulated the low pressure AC lines before I reinstalled them to reduce the amount of heat they absorb from the engine compartment. The less heat the refrigerant absorbs, the less pressure the compressor will build and the less power it will take to run.

Then I turned my attention to the condenser. Since it was from 2005 and the car had over 220K miles on it at the time, the fins were bent beyond repair by flying debris. Even though the condenser didn't leak refrigerant, I replaced it with a new Denso condenser, which cost around $60 with shipping. In my opinion, replacing the condenser while the system was open was well worth the money to improve efficiency and prevent leaks in the future.

So once I reassembled the system, I evacuated it overnight with a vacuum pump to remove any air or moisture and I refilled it with 4 ounces of double end capped PAG oil, which apparently has better lubricating properties and isn't hydroscopic. I then added 19 ounces of pure R134A refrigerant, which is within the factory spec of 17.6 to 19.4 ounces.

After all of that work, the AC worked pretty good, I would say at least as good as when the car was new, although this car's AC never worked great, especially at idle.

But about 1 month later, I decided to try Envirosafe Industrial R134A replacement. It is basically a 60/40 blend of propane and isobutane, so it's a flammable refrigerant and I wouldn't suggest trying it.

So I took the car to a shop to have the refrigerant recovered, then I took the car home, evacuated the system for over an hour to remove any remaining R134A refrigerant, and filled the system with about 7 ounces of Envirosafe Industrial R134A replacement, which they told me is approximately equal to 19 ounces of R134A.

I immediately noticed that the system cooled off quicker, and it got colder at idle. Also, this refrigerant runs at a lower head pressure than R134A, so the AC compressor doesn't draw as much power to compress it. Not only will that improve gas mileage, but it should extend the life of the system too.

But as soon as I drove it on the highway, I noticed that the compressor cycled on and off more. With R134A it pretty much ran constantly on a hot day, but with this refrigerant it cycles on and off instead of running constantly, which should save some gas.

I also "feel" like the AC doesn't create as much drag while it is running with this refrigerant due to the lower head pressure, but I can't prove that.

Anyways, let me know what you think about this :)

It should be completely safe for people to try out. The auto ignition temperature of the gas is above 1200* F. Although the can itself should be stored below 125* F, but I think that is so the pressure does not build up too much in the can.

https://www.es-refrigerants.com/docs/13007_499.pdf

Edit: After reading some reviews from people who have used this product in their vehicles, most have said that it works better than R134a. An occasional HVAC person would say that nothing but regular 134a should be used, but I haven't read of anyone having issues with it. I think I might try this product in my vehicles now.

Thanks. It does seem to work better, it is better for the environment since it is ozone safe and it has almost no GWP, and it should be better for the system's longevity. But my biggest concern would be what would happen in a front end collision. If the condenser is smashed and wiring sparks or something... That could end badly. Or the less likely scenario where the evaporator goes bad and dumps all of the refrigerant inside the car. A spark from a relay or switch could also end very badly.

I remember reading a forum where someone apparently used this refrigerant in their car to replace R12 (IIRC an old Porsche) and somehow a hose was sliced by the cooling fan, I think while they were running the car on a dyno. It supposedly ended up starting a fire. I wish I could find that forum.

EDIT: This wasn't the forum I was looking for, but here is an article about the incident: http://www.imcool.com/articles/airco...erant_Fire.htm

I think if you keep your vehicle well maintained you have little to worry about. In the event of a front end collision... Keep a fire extinguisher handy in your car if you're worried about it :)

Edit: I think I have little to worry about because my evaporator is located in the rear of my engine bay and I am planning on buying a heavy duty front bumper. As far as that isolated incident goes... I suppose if your AC hoses run near any fans then this idea poses a few risks.

I don't think it is that much of a risk either, but I am not going to say that everyone should start using it and that there is no risk at all either because that's not the case at all. According to the article above, a guy apparently almost lost his car because of a fire due to the use of this refrigerant.

May I ask what precisely you are doing about the mass of extremely reactive hydrocarbons at the rear of the vehicle?

If you carry a 2pound fire extinguisher you should be good.

Not a good comparison IMO. The fuel tank and lines are well protected and would be much harder to damage than the AC condenser, which can easily be damaged in a 5 MPH crash or by flying debris as I know first hand. If the back of the car is hit hard enough to damage the fuel tank, you would have bigger problems than spilled fuel.

Also, the AC system runs at much higher pressures. The fuel system usually runs at about 50 PSI maximum (although some systems run at a higher pressure), but the AC system’s high side can easily exceed 300 PSI on a hot day.

Not much to worry about. In reality, you have 7 ounces of "fuel" in the system. Even if it burned or exploded. What is the likelihood of damage from 7 ounces of fuel burning? If it even combusted at all...

If my car didn't use special refrigerant I would do this for sure.

Thanks for the input! I am not very worried about it either, but I wanted to discuss the possible risks as well. I guess my biggest concern would be if the condenser or a refrigerant line was punctured or damaged and the escaping refrigerant ignited, the resulting blowtorch could ignite surrounding combustible materials.

Since it is the industry I work in, consider natural gas leaks. It is not very often they ignite, many go entirely unnoticed for years. Particularly on small leaks, the gas would dissipate so quickly to a percentage where it is no longer a threat.

Great point, thanks! However, there is a tiny difference here- Natural gas is less dense than air, so it floats up and dissipates. On the other hand, propane and butane are denser than air, so they tend to settle in low areas and concentrate. Realistically that probably wouldn’t be much of a factor here, but I figured I’d mention it anyways.

Another idea
 

I am going to get a Mishimoto fan shroud kit for my car to help improve airflow through the radiators. Not just to help the AC operate more efficiently at low speeds, but also to help the engine cool better in traffic and at low speeds. Even with my Mishimoto radiator, the coolant sometimes heats up to around 210 degrees with both fans running when I am sitting in traffic with the AC on on a very hot day, which I don’t like.

Then there is the question of the extra power the Mishimoto fans would draw would be worth it for MPG. I would say yes, but I’m not certain. I can’t imagine that the Mishimoto fans would draw that much more power than the OEM fans do, but since they would improve airflow and therefore improve the efficiency of the AC system, but I am not certain.

Also gasoline vapors. It's good to be aware of the difference but if you've got a propane leak or NG leak in your garage it gets addressed in the same manner. Open a door or window and let it vent.

Flammable refrigerant kills 2 stones with 1 bird. Efficient cooling when needed, and instant heat when it bursts into flames!

Kidding aside, I'd consider it. The chance of fire seems pretty low, and the amount of refrigerant low enough that even if it did leak out and catch on fire, shouldn't do much damage.

I've shot camping propane bottles in a fire before, and it doesn't do much. Same with butane.

Coolant is flammable, oil is flammable, power steering and transmission fluid are flammable (my car had a PS hose recall for this reason), oil is flammable, and gas is VERY flammable. A little bit of propane shouldn’t be too scary.

That being said, you should keep one of these in your car anyways.
https://ecomodder.com/forum/attachme...3&d=1553793039

If you use a dry powder extinguisher, make sure to tip it back and forth every once in a while to prevent the powder from clumping on the bottom. You should be able to hear and feel it moving.

Lol thanks. However, if this video is real, I disagree that there isn’t enough refrigerant in the system to do much damage in the unlikely scenario where all of the gas leaks out into a confined space. https://www.youtube.com/watch?v=ANtAbkKrOuI

I think that the most dangerous (although extremely unlikely) scenario would be if the evaporator bursts while the car is parked and fills the car with flammable gas. Then the owner of the car gets in and starts it without knowing anything happened, and the spark from the ignition switch ignites the gas, causing an explosion while the driver is in the car. Again, I think that would be very unlikely though.

Meh, that mannequin seemed hardly phased, and I'm sure I've done worse to myself. Eyebrows grow back.

Window tint
 

I frogot to mention that I also had the side and back window tinted with 3M Crystalline 40% window tint, which helped a lot. I am hopefully going to get the windshield tinted with the same but the 70% version. Not only will it help to keep the car cooler, but it will also help keep me from getting blinded by the sun

The refrigeration industry has been having a very hard time in the last few decades. The patents have run out on the current batch of gases and the profit margin has dropped. Considering the gwp issue, along with flammable gas concerns, there are not many viable options. R-410a was a stretch back when it got vetted.

In Europe and Asia, the powers that be have decided that stuff like propane and butane is ok for small appliances. The commercial market is especially all in on building refrigerator and freezer units that are filled with hydrocarbon refrigerant. The supermarket industry is leaning on the government to increase the limit on the refrigerant charge, so they can run the freezer aisle and back of house coolers with natural refrigerant.

Natural?

Yes. Propane and butane are naturally occurring gases

If I actually used my A/C here I'd consider it, but the average high temperature in summer is only around 80 degrees, and humidity isn't too bad.

Thanks for the clarification.
The word natural has unfortunately loat most of its meaning due to marketing BS.

I wonder if some of the lines can be coated with ceramic to reduce heat entry to the AC system.

Of course the AC techs don't want this being used. It is freely available. And I get a kick out o fpeople that talk about what will happen in a front end crash. Worst case, you will have a very short duration flash fire. And you are in the car....behind the FIREWALL.

I may try this on the cab AC of my 87 Toyota Sunrader RV.

And there is one more benefit not yet mentioned. Propane is a ginormous molecule. Much less prone to leaking at seals. And if it does leak very slowly, who gives a sheeet? It is dirt cheap.

Great idea! You could actually coat the low pressure lines (The large pipes that get cold with the AC on) in ceramic, and it would improve the efficiency of the system, at least a tiny bit. It will reduce pressures and temperatures inside the system the same way that reducing the fan speed will, meaning that more of the system's capacity can be used to cool the inside of the car.

What I did is I used pipe insulation from the hardware store to insulate the metal parts of the lines where possible, which seems to work pretty well. However, I didn't want to use something combustible (foam pipe insulation) on the part of the AC line that goes down to the compressor because it runs right past the exhaust header, so what I did instead is I cut an old heater hose down the center, put it over the pipe as well as I could, ziptied it in place, and wrapped the whole thing in electrical tape.

Not pretty and I'm sure it isn't as effective as thick foam pipe insulation, but I am sure it is at least somewhat effective since the heater hose is pretty thick rubber, but most importantly, it won't cause a fire. I am probably going to try to find a better solution though since the heater hose is ugly and it doesn't fit well around the bends.

The oil for r134a is flammable, and when combusted, basically creates mustard gas- which is deadly at a few PPM. r134a runs at higher pressures so it's more likely burst and spray out onto something hot.

My last purchased car came with propane, if you've got an old car it's basically your only choice.

Exhaust wrap would work. You could even wrap that in thick aluminium heat shielding. Reflect the heat before it gets there.

I believe the r12 / r134a substituters were using about 70 percent butane and 30 percent propane to achieve the same vapor pressure in the system. As usual, a txv works better than a fixed orifice, but is less tolerant of being undercharged.

According to the MSDS sheets I have read, R12A (the drop in R12 substitute) as well as Envirosafe R134A replacement are made out of 60% propane and 40% butane.

My AC is currently empty. Leaking core. Once I've fixed it, I can just use R600a instead of R134a (which my car normally takes)?

I never tried it, but I am sure it would work to some extent and it shouldn’t damage anything. However, I would personally use the Envirosafe R134A replacement or something simalar for the best performance unless you just want to try it.

If you choose to try it, keep in mind that you won’t charge the isobutane to the 30-50 PSI that you would normally charge to, the pressure will be much lower. I am not sure, but normal low side pressure (depending on a lot of things) may only be about 8-10 PSI or so according to this pressure temperature chart: https://www.raprec.com/download/reso...pt/r600a...pdf

If you want to try this, I would suggest that you charge for the lowest vent temp since I am not sure what the pressures should be and you probably won’t find much info on this. So basically that means add refrigerant a little at a time with the AC running and the fan on high with a thermometer in the vent. Once the vent temp starts to increase, remove a little refrigerant until the vent temp is at the lowest. R600A can be vented to the atmosphere, so no need to recover it.

I hope that made sense. If you have any questions, feel free to ask.

Thanks. I was under the impression Envirosafe R134A replacement was essentially r600a. Being both LPG based.

I'm from the UK so getting Envirosafe R134A replacement is expensive. R600a is easier to get.

https://www.es-refrigerants.com/docs/59264_645.pdf

That makes sense. Feel free to try it then. I think the worst thing that would happen is that you would need to remove the R600A and use fomething else if it doesn’t work well. And at least in the US, you can legally vent R600A into the atmosphere

Refrigerant grade propane is r290. It has roughly the same pressure range as r22. Butane and isobutane both have lower pressures than r134a. If you are running a txv you'll have to run a blend.
http://acprocold.com/wp-content/uplo...rt-33776F1.jpg

You are right! Another thing to keep in mind is the maximum pressure that the system is designed to hold. I imagine for a R134A MVAC system the design pressure would probably be about 150-175 PSI on the low side and about 350-400 on the high side, although I'm not sure about those pressures. But if you exceed the maximum pressure that the system is designed for, bad things can happen.

This shouldn't be a problem if you use an R12 or R134A drop in blend or straight R600A, but this CAN be a problem if you blend your own refrigerant, especially if you increase the proportion of propane, the higher pressure gas, or for that matter if you try to use straight propane as some people have suggested to replace R12.

On my car, the pressure relief valve on the back of the compressor looks like it would spray refrigerant right on the exhaust header if it were to blow, which could end badly as is with R134A and oil mixed, but a flammable gas would make that worse.

Anyone have an ide of roughly how many liters per minute or hour are circulated? In liquid form? Or mass?

I ask because my old car was converted to LPG, and it would use engine coolant to vaporize the lpg. I always thought that was a huge waste of its cooling potential. I wanted to modify the vaporizer and put it inside the car or pass it theough the ac vaprizer. But never got around to doing the calculations if it would be worth it.

Checking the average, it looks like it was 14.8 liters of lpg per 100km.

I have no idea how much refrigerant the system actually circulates, but that would vary a lot based on the vehicle, the size of the AC system, ambient temperatures, engine RPM, airflow, and even vehicle speed.

However, I am thinking if you have a rough idea of the system's capacity (BTU per hour), you could calculate how much refrigerant would need to circulate based on the refrigerant's latent heat of vaporization in BTU's/LB. Basically that is a measurement of how much heat one pound of the refrigerant will remove if it vaporizes. Here is a chart of the latent heat of evaporation of some fluids, including refrigerants: https://www.engineeringtoolbox.com/f...eat-d_147.html

So basically I think you would need to figure out how many pounds of refrigerant need to be circulated per hour to get to the refrigeration capacity of the system (in BTU's per hour) based on it's latent heat of vaporization, then convert the pounds to liters. I'm not sure how well that would work though.

So here's an example: The system has an output of 12000 BTU and uses R22, which has a BTU/LB of 100. Divide 12000 by 100, and you get 120 pounds of refrigerant per hour needed to provide that cooling capacity, or 2 pounds per minute. Then you would figure out the density of R22 and convert to liters. I think that should work anyways :)

2 pounds per minute is very very roughly 1 liter per minute, the car would need to be burning 60 liters per minute...

Which would be a 1/4 efficiency gain for that particular car.

2 pounds of propane per minute would be much more than 1 liter per minute because of propane's low density. 1 pound of propane is about 0.23 gallons, so 2 pounds of propane would be about 0.46 gallons, or about 1.75 liters or so.

Also, as stated in the post, the 2 pounds per minute that I calculated was using R22 refrigerant and a 12000 BTU AC system just as an example.

Also, I have read that a typical car has a 3 to 5 ton AC system, which would be 36000 to 60000 BTU per hour.

A bit of hose could be used to redirect the breather outlet. Gas is a much lower ignition hazard than a pool of liquid. Besides, I've never heard of an exhaust manifold catching fire :D