Aircon Discussion

[frank rabbets]

Just read the FWM which confirms what you say but still confused. If the refrigerant in the sight glass is in liquid form does this liquid mix with the oil to become one liquid ? Or are the two not miscible ?

I take it refrigerant = gas. If the A/C is not running and the car has stood overnight the gas pressure should be equal throughout the system. If the gas level is low the only way to increase it is to add more but surely the pressure would increase?

The FWM says if compressor, evaporator, condenser or drier are removed these should be drained and the oil measured and an equal quantity returned to the system plus a bit more I suspect as it is impossible to get all the oil out of the old parts.

My genuine Denso/Toyota seals have arrived but I'm too tired to look in the box .

 

[StarCruiser]

I'm saying refrigerant because it can be gas, vapour, and liquid dependent on pressure and temperature. When you buy refrigerant it is liquified in a metal cylinder or 'bottle' and you weigh it in. You can introduce liquid into the suction of large systems without harm. Whether it's a 5kg bottle or a 200kg bottle, provided the volume of the bottle is correct for the amount of liquid then you will fit the liquid in.

A bit like LPG (which can be used as a refrigerant) is a liquid in the gas bottle (you can hear and feel it slopping about), towards the end of the bottle when the liquid boils off (you have trouble getting enough pressure out of a cold gas bottle) into gas then the pressure drops away. The crux is that the gas is a liquid at room temperature at a certain pressure. Once it is a liquid, at the right pressure, then you simply fill up the space with liquid until no more will fit. Some of the bigger systems have bullseye sight glasses in the receivers and you can see the liquid flowing in like filling a bath.

Some systems equalise after sufficient time has elapsed, such as a domestic fridge. In a larger system (not sure but this may be the case on vehicles) you have a solenoid valve which shuts off the liquid line after the receiver and before the expansion valve (domestic refrigerators have a calibrated orifice in the form of a capillary tube instead of an expansion valve). The whole contents of the system can be stored and isolated in the receiver. The whole system can be brought to low pressure to be opened and worked upon. The average pressure in the system will not change unless refrigerant leaks out whereas pressures are radically different across different areas of a running system.

 

[StarCruiser]

Put simply, if you want to know whether or not your system is full, you don't need a pressure gauge, just look in the sight glass for it to be full of liquid for most to all of the time.

 

[frank rabbets]

Got it. I'll double check my glass today with the system running. I've been so obsessed with oil amount that I totally forgot that the whole idea of a fridge was to compress gas to a liquid then let it out through a pinhole to produce cold.

Like I say I've changed 2 condensers and 2 receivers and have not replaced the oil lost as I should have done so I'm off to the A/C place to get some oil to add. A bit of guesswork. The system must be very low on oil but has not seized yet.

When you compress propane into a bottle you can start to feel it slopping around inside. The more gas you put in the higher the level of the liquid. Say the bottle is half full of liquid (gas) , what is in the top half of the bottle???? The pressure is constant throughout the inside of the bottle so why isn't it all liquid or all gas?

 

[StarCruiser]

Poor Service From Main Dealer

When you compress propane into a bottle you can start to feel it slopping around inside. The more gas you put in the higher the level of the liquid. Say the bottle is half full of liquid (gas) , what is in the top half of the bottle???? The pressure is constant throughout the inside of the bottle so why isn't it all liquid or all gas?

It depends upon temperature. At room temperature there will be an amount of vapour or gas or both that has boiled off from the liquid. Just like in a petrol tank or for that matter a bathroom with a steaming hot bath in it. The difference being that there is no air in either the refrigerant or the LPG bottle because it has been evacuated before it is filled.

At a critical low temperature, the bottle could contain only liquid with a vacuum above it. It would also be possible at that temperature for the liquified gas to remain stable as a liquid and be poured. For this, think of liquid nitrogen where it can be poured at room temperature from a highly insulated flask and begins to boil off over the edges of the beaker it is poured into as a vapour you can see, disappearing into the air as it warms further and becomes a gas.

 

[frank rabbets]

In that case, with liquid propane in a bottle, a pressure gauge would not act as a contents gauge? Is that right? My oxygen cylinder has a pressure gauge which acts as a contents gauge. Does this mean there is only compressed oxygen in the bottle?

I thought I might be able to add oil to my system through one of the valves on the compressor without having to release the gas. Any thoughts on that?

The 80 air con, and I guess all car A/C systems, do not have taps so you can compress the gas to a liquid, contain it somewhere, and then open up part of the system to work on it. If any part of the 80 is opened up there is no way you can save any gas.

 

[StarCruiser]

Poor Service From Main Dealer

In that case, with liquid propane in a bottle, a pressure gauge would not act as a contents gauge? Is that right? My oxygen cylinder has a pressure gauge which acts as a contents gauge. Does this mean there is only compressed oxygen in the bottle?

The gauge will read at a set temperature and I don't think (though I may be wrong here) the cylinders contain liquid oxygen. However there are rough gauges on propane to indicate when empty but other than that not overly accurate. Bottle weight (or the weight of the contents) as it is sold in, would be a far better indication of content.

I thought I might be able to add oil to my system through one of the valves on the compressor without having to release the gas. Any thoughts on that?

You would need a refrigerant oil pump and to pump it in without introducing any air or moisture by letting some gas out while you attach a line that is full of oil from the pump.

The 80 air con, and I guess all car A/C systems, do not have taps so you can compress the gas to a liquid, contain it somewhere, and then open up part of the system to work on it. If any part of the 80 is opened up there is no way you can save any gas.

Correct. Valves cost money. Before entering the system the refrigerant should be reclaimed (removed) first and either disposed of or replaced into the system. The first being the best overall as you don't know what you are removing with the refrigerant.

 

[frank rabbets]

Thanks for your help on this. It's coming back now. I did do physics at school bot that was 1962 .

 

[StarCruiser]

Poor Service From Main Dealer

Thank you Frank. It's made me dust off the memory banks to be able to put together useful explanation on a topic that is not my primary subject. Glad to be of some help

Looks like my one remaining overworked brain cell is still holding up [emoji4][emoji6]

 

[frank rabbets]

I need to correct myself on the Workshop Manual. It says to save and measure the oil from the compressor and add the same amount back in + 20c.c. With the other components you do not measure the old oil, you just throw it away and add a fixed amount. I think my system should hold about 200c.c. but I've replaced the condenser and drier twice and should have added 100c.c. for these 4 items. My system must be half empty. I'm sure several pumps have been seized due to ignorance on this topic.

I used to visit scrap yards in the early 60's to search for motorcycle parts. There was no health and safety and most owners would let you go around freely and find what you wanted. I used to buy old giant compressors, which I assume were from butchers cold rooms, and take them apart. I built one compressor for my garage and used an old oxygen cylinder as a tank. The wall of the cylinder was about 5/8 inch thick. I had to drill a hole in it for the output pipe.

SC it will be interesting to hear about your system when you get round to fixing it.

 

[StarCruiser]

Reminds me of the early 90s when I lost my job and started helping out at the local mower repair shop. The guy had an ancient air compressor that had been left there. It was mounted on a WW2 bomb casing as a receiver! [emoji33] I furnished him with a second hand Hydrovane instead.

 

[chapel gate]

" I'm sure several pumps have been seized due to ignorance on this topic."

I agree, thats why i keep bringing it up..

 

[Shayne]

My condensor was crushed , i have replaced it and had planned to go to the nearest service place and ask them to fill it up . I don't really care about my a/c but if its there it may as well work . So having read this thread in fits and starts with eyes wide shut should i ask for a flush and fill to include 6floz of oil ?

 

[clivehorridge]

My condensor was crushed , i have replaced it and had planned to go to the nearest service place and ask them to fill it up . I don't really care about my a/c but if its there it may as well work . So having read this thread in fits and starts with eyes wide shut should i ask for a flush and fill to include 6floz of oil ?

If they're half worth their salt, Shayne, they should do a full diagnostic first, and a 20 minute vacuum leak test, and then tell you the full status.

 

[chapel gate]

My ensor was crushed , i have replaced it and had planned to go to the nearest service place and ask them to fill it up . I don't really care about my a/c but if its there it may as well work . So having read this thread in fits and starts with eyes wide shut should i ask for a flush and fill to include 6floz of oil ?

8 floz, dont forget the evaporator, 2floz per component is a good rule of thumb. If you have exact amounts from an fsm etc go with that.

 

[StarCruiser]

Putting on vacuum is only a basic leak test. The system needs to be pressurised with dry nitrogen to a decent pressure to see if you have any leaks. Then vaccing out is essential before adding the refrigerant to ensure only refrigerant is in the system. If the system has been open for any length of time (hopefully open ends were sealed soon after separating them) then the vacuum should be applied for longer to boil off and remove any moisture as moisture will freeze in your orifice…and you certainly don't want that. [emoji33][emoji33][emoji33][emoji6]

 

[frank rabbets]

I sent a p.m. to Dave 2000 and he says some machines actually recover all the oil and put the whole 7 ounces required for the single system 80 back in. I also talked to Toyota Stourbridge. They have a new machine they think can remove all the oil and put the total in but they are not too sure how to use it yet. They say to pop over and see so that's what I'll do.

 

[StarCruiser]

Sounds like it's worth a haggle to have them do a bit of training on your truck for free Frank. [emoji6]

 

[chapel gate]

Putting on vacuum is only a basic leak test. The system needs to be pressurised with dry nitrogen to a decent pressure to see if you have any leaks. Then vaccing out is essential before adding the refrigerant to ensure only refrigerant is in the system. If the system has been open for any length of time (hopefully open ends were sealed soon after separating them) then the vacuum should be applied for longer to boil off and remove any moisture as moisture will freeze in your orifice…and you certainly don't want that. [emoji33][emoji33][emoji33][emoji6]

And replace the dryer if the system has been left open for any length of time.

 

[Pumpy]

The best bit of advice I got for the air-con on my 80 was to take it to somewhere old-school that knows what they're doing, rather than one of these places with a machine.

Bloke at the aircon place said "It's an R12 system, needs to be done manually" Must have been a while since they'd done one because the main chap got all his younger staff to watch him doing it while he explained what was going on, real interesting to watch. Mine had 3 leaks fixed, 20 min vac test, "deep system vaporisation" then 150ml retro min oil, 800 RS24 refrigerant added. gas cost £125 they added an hour labour (which wasn't bad considering they were at it an hour n 45mins) with the vat it was £198.

proper job done, so I was happy.

I was advised to keep it on all the time so the oil get round everywhere.