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Air Conditioning Maintenance and the Refill Cans.

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Tommi
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Air Conditioning Maintenance and the Refill Cans.

Post by Tommi » Thu Aug 04, 2011 9:45 pm

I have read a bit about the AC refill cans and seen some questions in various posts so I thought I would start a new topic and answer them in one place.

I have installed, fault found and recharged countless domestic and industrial refrigeration systems. Completed a 4 year apprenticeship in refrigeration and airconditioning and completed vehicular air conditioning course. I have however never used a "Death Can", but I know what they are about.

The reason the cans are based on pressure and not weight is that Refrigeration is based on Pressure=Temperature (and vice versa). Different refrigerants (and there are A LOT of them out there) have different P/T relationships but all follow the same rule, high or low pressure equals high or low temperature respectively.

The actual measured amount of refrigerant required in a system to bring that system to the correct pressure is irrelevant (however important), it's the pressure that is important. In domestic and industrial applications we weigh gas into a vacuumed system, accurate the the gram, to ensure the precise pressure will be obtained whilst running.

Air Conditioning is ideally a 100% sealed system, leaking no gas, and theoretically recycling that same gas for its entire life. The problem is that in cars the vibration causes the refrigeration pipework to crack and leak so to get around this the use of rubber seals are used. The rubber gets worn and/or dries and cracks with lack of oil (I'll cover this in the next paragraph) so the gas leaks out giving the system a lower pressure and therefore a lower.... temperature! Good, we are learning.

The 25-45psi pressure guide on the can, relates only to the optimal working pressures of the system, it's best to have it at 40-45psi as this will allow for future leaks (if it leaks once, its going to leak forever unless you repair the leak). The refill can is the cowboy way of doing the job. Realistically the system should be repaired, vacuumed and re-gassed. But the can works so people use it. From my experience most garages will just vacuum and gas your system to its specs, this is better but not repaired so it will leak (usually very slowly). They offer this at "cooler or free" as they can charge you for repairs if it doesn't work. In my experience, leak sealant foam aka 'system safe leak sealer' rarely (if ever) works for very long.

The best way to avoid having to regas is to run your AC occasionally (lets say once a week, even when its freezing out). This will migrate the oil to the seals lubricating them :D. That's the oils secondary job, the first being lubricating the AC compressor, this is where the majority of the oil is stored and is usually enough to last the life of the system regardless of leaks. So the oil in the can is not hugely important, but good none the less.

Refrigeration techs refill systems on the liquid line*, which is neither the High pressure or Low pressure side referred to in other posts. Filling on the low side floods the compressor with liquid refrigerant, which is very bad, compressors can't compress liquid! Filling from the high pressure side is ineffective and dangerous, when the compressor is running its pumping high pressure (high temperature!) refrigerant directly into your can.

*Or on a vacuumed system from the high pressure valve whilst OFF.

If you don't have a liquid line access valve (I haven't looked but would be pretty sure the RX8 doesn't) you need to use the vacuumed technique. This also removes all contaminated air, moisture and unbalanced blends of gas from the system AND tests for leaks. Even if we did have a liquid line the can pressure would not be enough for charging.

My last and most boring point is that Car Air Con gas is R134a which is a manufactured blend of gasses, when gas leaks it does not do so equally, resulting in unbalanced (less effective) gas remaining. Top it up with more unbalanced gas and you will make it even more ineffective.

IN SUMMERY

- The cans are the worst of 3 options but cheap and temporarily effective. We live in a cold country so how important is car AC to you?
- Goto a dealer and get a vacuum and regas for best value for money. This is what I would do.
- A full repair will always be the longest term option and of course, the most expensive.

As you can see I'm an AC nerd. This is mainly here for reference but feel free to ask questions.

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tonybangbang
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Re: Air Conditioning Maintenance and the Refill Cans.

Post by tonybangbang » Thu Aug 04, 2011 11:01 pm

i had to replace my aircon hose's and rad what would u recommend i do ? replaced myself btw and at this moment in time its dam hot i was going to let kwik fit or budget refill it but from reading ur post am not to sure now

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Tommi
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Re: Air Conditioning Maintenance and the Refill Cans.

Post by Tommi » Fri Aug 05, 2011 5:27 am

As long as they do pull a vacuum on the system first it will be fine, this will check for leaks at the same time. The moisture in the air that is now present in your system needs to me sucked out to prevent the compressor being destroyed. I'll find out is Kwik fit do this first (they should!).

Update: Spoke to a guy from quick fit today who assured me all existing gas is removed before filling, when i questioned further he did say a vacuum was pulled. I would make sure this is done when you go but as for being worried, don't be!

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