Air con re-gas numbers with a mish mash of parts

[madmog]

I'm installing Air con in my W114 and am using parts from various places - an aftermarket blower, Fiat 500 compressor (because small and bigger won't fit) and whatever condensing radiator will fit. This car never originally had air con. All parts are new. 

Reading around gassing these things, each vehicle has a sticker stating the amount of gas to be added; presumably based upon the volume of all of the parts. So, if making a one off, is there a formula or technique for determining the amount of refrigerant to add? Similarly, the amount of air con oil to add to a dry system?

I have a vacuum pump already and the air con gauges seem cheap enough though I'll probably leave it to a professional but even then I would want to know the volumes to see if the professional is in the right ballpark.



Thanks

[Rich]

I’m curious to see what pressure cutout sensing system you will use, having only briefly dabbled in A/C (beyond replacing parts) I know that you can’t run a compressor constantly for long before the system goes a bit wonk. I was doing some trigger testing on a Corsa a few years ago (turned out to be an engine ecu fault not triggering the AC auth) and was running the compressor by way of a bypass and it eventually (I assume) overpressureised the high side and stalled the compressor. 😬 As for calculating capacity, hopefully someone clever will have something useful.

[colnerov]

Hi, Get someone to charge it that does plant or similar equipment, because there will likely be used to no label with content information. A good operator will have an eye for it, by reading the gauges as to quantity installed. They will also know from that the oil needed, have dye added as well because it will aid fault finding leaks in the future. As said you will also need high and low pressure switches to operate and protect the system. also speak to them about an appropriate condenser because they will have a catalogue of options and a universal one may be suitable. They can make up hoses as well.

Colin

[madmog]

Apr 25, 2023 15:36:46 GMT Rich said:

I’m curious to see what pressure cutout sensing system you will use, having only briefly dabbled in A/C (beyond replacing parts) I know that you can’t run a compressor constantly for long before the system goes a bit wonk.

Something called a Trinary switch which came with the cockpit unit from Car Builder Solutions. To paraphrase their catalogue:
A three function pressure switch ... one wire will turn on the condensing radiator fan whenever the air con is used ... the other two provide a safety cut-out for the compressor if the pressure is either too high or too low. Costs about £22 but you would need to plumb it in. I don't have an ECU to get upset so its straightforward. I don't know if it could be used in conjunction with whatever the your ECU is (supposed to be) doing to control pressure or could be used instead of the ECU's air con sensor, perhaps using the same port. 

Apr 25, 2023 16:33:55 GMT colnerov said:

Hi, Get someone to charge it that does plant or similar equipment, because there will likely be used to no label with content information. A good operator will have an eye for it, by reading the gauges as to quantity installed. They will also know from that the oil needed, have dye added as well because it will aid fault finding leaks in the future. As said you will also need high and low pressure switches to operate and protect the system. also speak to them about an appropriate condenser because they will have a catalogue of options and a universal one may be suitable. They can make up hoses as well.

Colin

Thanks Colin, I'll use the vacuum and gauges to at least check for leaks so I don't waste someone's time. I actually have a hose maker which is a great piece of kit off Ebay. So I'm all set but for the gassing. Oh, and getting the engine running and all the wiring and interior.

[kevins]

You can do it by looking at the operating pressures, I think there's a table in my Range Rover manual, I'll see if I can find it tomorrow, most A/C specialists will be familiar with doing this, it's what you do when replacing R12 with 134A etc.

[Rich]

That switch/sensor arrangement sounds ideal, a neat solution to the problem with retrofit.

[kevins]

This is what they specified for the fill on a R12 Range rover classic, I use these figures a rough guide on most things, mainly making sure I don't exceed the high side numbers (usually leave a 20-30 psi margin on old systems), some of the modern gasses / systems  go a bit higher  but I tend to start around here and add a bit more if it's not effective. Recently I've been using R290 which is refrigerant grade Propane and what a lot of the top up gasses sold on ebay are (it's not damaging to the environment if it leaks out so very good for a system test), I've put it in the range rover and street KA (which was R134A) both seem to run higher low side pressures than specified in the table with this but the Aircon works fine.



Found a similar tabe for 134A




bear in mind you shouldn't exceed what the parts were originally designed for so if you have a R12 evaporator and expansion valve I would stick to the R12 pressures etc.

[jonsey]

I used to do a/c charge determination tests for an oem manufacturer. What you are trying to achieve is enough gas back to the compressor so it doesn’t try to compress a liquid and enough liquid at the expansion valve so that it can change to a gas and you get the benefit of the latent heat when the liquid turns to a gas.

We would run the car in a climatic wind tunnel and at say 35- 40degc with 200 gram charge, wait until all press and temps are stable then add 50 grams and repeat etc. When all pressures and temps are plotted against charge amount on a graph you will get a level plateau. The correct charge amount would be the middle of the plateau giving you say a 50g tolerance either side. This is the info you usually see on the label under the bonnet

I doubt you have access to a climatic wind tunnel so I would say as long as your not going so high a charge amount as to be bouncing off the high pressure switch 28bar ish, or so low as to be damaging the compressor due to low oil circulating, it will be fine. In between the limits the only issue is bad performance-not old enough to too good- evaporator freezing and the a/c cutting. Middle field is good.

Like others have said a good a/c fitter should have floating about in his brain an idea of what cars have what charge amount and what size components they use. He can then make an educated decision

I’ve not touched this stuff for 14 years but If it was me I’d start at 500 gram and add if not cold enough.

I will also add make sure all safety switches are utilised. A/c shouldn’t be able to operate without the blower on. Have the electric fan on when a/c is on. You will see some silly high pressures in the system of things go wrong

Good luck. Let us know how it goes