A/C - topoff versus complete discharge

[440Magnum]

Originally Posted By: Vikas
Originally Posted By: 440Magnum
but if the schrader valve core itself is leaking you can only replace it with the system discharged.


I thought that was the whole idea behind that tool which lets you replace the schrader valve core WITHOUT discharging the system.


The earlier link was the first time I've seen one of those. Slick little booger!

 

[Vikas]

Ya, RealFixesRealFast on youtube has a video on that tool. I suspect it is NOT cheap.

 

[friendly_jacek]

Not to steal this thread, but I unscrewed the plastic tops from Schrader valves (service ports) in my newest car, Prius with 6000 miles, and the same thing, slight pressure under the caps (you can hear a slight and short hissing sound when removing) and the freon sensor ($20 ebay item that actually works well) detects freon in the service ports. 3 of my 3 Toyotas do that. Is this normal or should I tighten them up?

 

[mechtech2]

Thos caps are lost or broken often.
But they are imnportant! Keep them on and in good shape.
They all seem to leak a bit otherwise at the valve.

 

[JHZR2]

The caps are part of the leak prevention system Ive read... In other words, they have o-rings and seal tight to prevent loss of refrigerant. If one has a lot of loss and the system is seeing loss as a result, then it may be worth a change.

Id be most concerned with trapped air in the refill lines when topping up. Need to figure how to purge the air out without loosing a lot of $$ refrigerant to the air.

 

[mattd]

complete service. I had a ford van come in today that was 4 LBS OVER filled...

 

[Drew99GT]

Originally Posted By: mattd
complete service. I had a ford van come in today that was 4 LBS OVER filled...

Did the A/C even turn on? If so, I bet it was LOUD!

 

[friendly_jacek]

Originally Posted By: friendly_jacek
Not to steal this thread, but I unscrewed the plastic tops from Schrader valves (service ports) in my newest car, Prius with 6000 miles, and the same thing, slight pressure under the caps (you can hear a slight and short hissing sound when removing) and the freon sensor ($20 ebay item that actually works well) detects freon in the service ports. 3 of my 3 Toyotas do that. Is this normal or should I tighten them up?


I used my AC manifold gauges and the pressures were by the book on the oldest car. I guess what I observed is totally normal!

Since I use the gauges rarely, should I purge the refrigerant from the hoses?

Right now, both blue and red hoses are pressurized (the gauges have a cutoff valve at the connections).

 

[mechanicx]

Originally Posted By: paulo57509
I just finished converting my '92 Lumina over to R134a. I thought it was a good time to do the conversion because the compressor failed. It didn't fail in the typical "black death" way and didn't circulate debris through the system. From the looks of it. it lost a seal and with it the oil and refrigerant.

What a two day ordeal.

Now I know why A/C service is so expensive to have it done at a shop.

To flush all traces of the old oil from the system, I flushed the evaporator and condenser (removed from the vehicle) and flushed the hard lines. The hose assembly I replaced with new.

I filled the replacement compressor and new accumulator with BVA 100 (POE) oil, evacuated and recharged with 24oz. of R134a from suicide cans (just refrigerant....NO oil or sealer). Twenty-four ounces is about 70% of the system capacity of R12 for this system so I should be good here. High and low side pressures are approximately 150psi and 30psi with the cooling fans running, respectively.

Ambient temps were around 70F and the system is blowing 40F. We'll have to see how it performs when (if?) the temps start to soar this summer.



You probably did a lot more work then you had to though. If there was not a failure with contamination it is not required to flush the system and actually the manufacture doesn't recommends flushing. It's also not necessary to remove all the R12 oil. If you can get it out that is good though. You want to shoot for 80-90% of capacity of R134a, with the high range if you removed all the R12 oil. Better to be lower than higher though. I think PAG 150 is what's recommended for the this system but POE should work OK. I don't mean to sound like I'm criticizing your work as it sounds like your system is working good. Those GM R12 systems seem to convert to R134a pretty well.

The things to watch out for with topping up with cans have been covered. If you use straight refrigerant and don't overcharge, purge air out of the charge hose etc, top ups can work just fine and are not as bad as a lot of A/C techs make them out to be. Of course it is always best to pull a vacuum and get any moisture and air out of the system and start with an empty system get the full proper charge level in. But as long as you don't get air in or overcharge topping up with cans won't harm anything.

 

[mechanicx]

Originally Posted By: friendly_jacek
Originally Posted By: friendly_jacek
Not to steal this thread, but I unscrewed the plastic tops from Schrader valves (service ports) in my newest car, Prius with 6000 miles, and the same thing, slight pressure under the caps (you can hear a slight and short hissing sound when removing) and the freon sensor ($20 ebay item that actually works well) detects freon in the service ports. 3 of my 3 Toyotas do that. Is this normal or should I tighten them up?


I used my AC manifold gauges and the pressures were by the book on the oldest car. I guess what I observed is totally normal!

Since I use the gauges rarely, should I purge the refrigerant from the hoses?

Right now, both blue and red hoses are pressurized (the gauges have a cutoff valve at the connections).


But even if your blue and red hoses stay sealed your yellow center hose and the center of the manifold guage will be exposed to air right? So I think ideally you will need to purge the hoses. You might have a can tap on the yellow hose that might seal but you have to open it to hook it up to a can.

If you don't have a vacuum pump to purge the manifold gauge, I think it is easier to just use a short charge hose from the can to charge. True you won't be able to see the low-side pressure when filling but that is of questionable value anyway. Or maybe just open the manifold's low side valves to purge the air first before filling the system, is what I'd do.

 

[wtd]

Originally Posted By: mechanicx
Originally Posted By: friendly_jacek
Originally Posted By: friendly_jacek
Not to steal this thread, but I unscrewed the plastic tops from Schrader valves (service ports) in my newest car, Prius with 6000 miles, and the same thing, slight pressure under the caps (you can hear a slight and short hissing sound when removing) and the freon sensor ($20 ebay item that actually works well) detects freon in the service ports. 3 of my 3 Toyotas do that. Is this normal or should I tighten them up?


I used my AC manifold gauges and the pressures were by the book on the oldest car. I guess what I observed is totally normal!

Since I use the gauges rarely, should I purge the refrigerant from the hoses?

Right now, both blue and red hoses are pressurized (the gauges have a cutoff valve at the connections).


But even if your blue and red hoses stay sealed your yellow center hose and the center of the manifold guage will be exposed to air right? So I think ideally you will need to purge the hoses. You might have a can tap on the yellow hose that might seal but you have to open it to hook it up to a can.

If you don't have a vacuum pump to purge the manifold gauge, I think it is easier to just use a short charge hose from the can to charge. True you won't be able to see the low-side pressure when filling but that is of questionable value anyway. Or maybe just open the manifold's low side valves to purge the air first before filling the system, is what I'd do.


My Robinair manifold gauge has a purge valve for the yellow hose so that you can purge the air out of the line when you change the cans.

The correct way to service an AC system that has stopped blowing cold because of a leak is to fix the leak and than vacuum the system down and recharge with the correct amount of refrigerant. Topping off can work but you never know how much you really have in the system and you probably won't get peak performance.

Wayne

 

[Craig in Canada]

IMO it depends on why you feel you need to recharge. If your AC "suddenly" doesn't work this spring, you need to diagnose the system and find out what's going on.

In my case, my 1998 BMW had very slow, gradual loss in performance over the last 4 years and the system had never been serviced. I try to run it every couple of weeks through the winter but often it's too cold for the system to run properly. In the heat of summer it could still blow cold air, but in high load situations (hot, humid, car parked in sun, fan on max trying to get cooling started) the vent outlet air was getting noticeably warmer than a nearly identical car 4 years newer. Under less heavy load the AC vent air was 38F.

Since there were no major leaks and a 4-5 year roll off of performance in maximum demand situation I just topped it up with a partial can of R134.

In Canada, it is illegal to sell R134a to non-licensed individuals. Thus it is unobtanium for us. It's not illegal to own, use, or bring across the border from the US where you can buy it at Walmart so that's what I did. I may have been tempted to DIY the whole evacuate, test replace valves, refill with oil and recharge by weight if the gases could be obtained. Considering my symptoms I sure wasn't going to give a stop $500 to deal with it. Either I was going to live with it or try a little top up...

 

[lairdwd]

Let's assume that you currently have a low charge on a 11 year old A/C that's never been recharged. In addition to 134a, should you add oil too?

For example, my wife's AC has probably 20% charge. Therefore, which one is better (i.e. cheaper/safe) to :

1) topoff with some r134a AND some quanitity of my own oil
2) complete discharge and recharge with fresh oil
3) topoff with r134a, and don't worry about the oil

 

[Craig in Canada]

Originally Posted By: lairdwd
Let's assume that you currently have a low charge on a 11 year old A/C that's never been recharged. In addition to 134a, should you add oil too?


Only if you lost some - which comes back to WHY is the system low. If it was leaking at the compressor and lost some oil, then you will need oil too. If it's been leaking very slowly from the Schrader valves then oil loss is not likely and the system will still contain the proper amount of oil. If whatever leak you have only leaks when the system is operating then oil loss is more likely than a system which leaks a little all the time.

You should maybe look for any telltale signs of oil leakage around major AC system features, welds, components, valves etc... If you don't find any, you *probably* don't need to add any oil.

Quote:

For example, my wife's AC has probably 20% charge. Therefore, which one is better (i.e. cheaper/safe) to :


Has 20% remaining, or is 20% low. 20% remaining is not "a little low" or a "small leak".

Quote:

1) topoff with some r134a AND some quanitity of my own oil
2) complete discharge and recharge with fresh oil
3) topoff with r134a, and don't worry about the oil


If it's 20% remaining, I vote #2, but add "find and repair the leak" to the list.

 

[mechtech2]

How does oil know not to leak at certain spots?
How does it choose only special locations?

 

[Craig in Canada]

Originally Posted By: mechtech2
How does oil know not to leak at certain spots?
How does it choose only special locations?


If oil pools where the leak is (like in the compressor), then some oil will leak out. If the leak is from somewhere else high in the system (like at a schrader fill valve) the leaking refrigerant won't carry oil with it.

I believe the oil gets aerosolized throughout the system to a certain extent when the compressor is running, which is why I mentioned that a leak which only occurs while the system is operating could lose some oil too.