Improving the AC system's efficiency

[EcoCivic]

Originally Posted by ratgreen

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.

[ratgreen]

Originally Posted by EcoCivic

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

[EcoCivic]

Originally Posted by ratgreen

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

[jeff5may]

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.

[EcoCivic]

Originally Posted by jeff5may

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.

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.

[teoman]

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.

[EcoCivic]

Originally Posted by teoman

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

[teoman]

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.

[EcoCivic]

Originally Posted by teoman

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.

[oldtamiyaphile]

Originally Posted by EcoCivic

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.

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