A/C - topoff versus complete discharge

[lairdwd]

There is a lot of confusion in the DIY area for A/C. I saw one tech refer to those self-service cans as "suicide cans".
I'm trying to figure out when can you safely topoff versus doing a complete discharge, vacuum, re-oil, recharge?

I'm trying to establish a "best practice" around DIY and A/C. For example, I'm guessing if you let the charge get too low, then topping off isn't ideal due to the system being empty and possibly having more contaminents. On the other hand, topping off before half the charge is gone may be ok. I'm totally guessing though.

At $135 a pop for a discharge, vacuum, re-oil, recharge - the more I can do myself, the better.

 

[Y_K]

I killed one unit by doing this. Does not mean you guaranteed to fail as I did, but risk/reward ratio is not there.
If there is a correct way of doing a top-ff, i would bet it is a temporary measure still.

 

[sasilverbullet]

I think it's all about risk - you weigh the cost savings of "doing it right" with the risk of just topping it off.

The risk lies in betting "the problem is a little low on freon". If in fact it is low because of a very small leak, then that's low risk. But if it's not pumping out cold air because the compressor is weak you can blow a hose or worse by overcharging it.

I had an older car that was 134a and each year I had to put a can in because of a small leak at the clutch. Never had any problems with it.

 

[lairdwd]

You also get into the oil compatability issue (if one) in the DIY can. My altima's compressor very clearly calls for PAG 100, yet the DIY cans contain ester or (what I think is) POE. Compatable? I think not.

 

[440Magnum]

If you have a good set of manifold gauges, a thermometer, and the pressure vs. condenser temp chart for the refrigerant the system uses, there's never any need to do a complete discharge unless the system is contaminated.

By "suicide cans" I think the tech is talking about the alleged fix-in-a can bottles that have sealer, oil, and other poo all mixed together and a cheesy little gauge. those are a great way to 'slug' a compressor or fill the system so full of liquid oil and sealant that it can't possibly work right. Adding pure refrigerant and doing it PROPERLY is not harmful to the system.

With regard to the validity of topping off at all... you have to remember that NO automotive A/C system is 100% leak free. Just like all cars burn some oil past the rings, ALL car air conditioners lose a little refrigerant past the rotating seal on the compressor shaft. Most cars can go 10+ years without losing enough to affect cooling, but some vehicles have less liquid storage volume in the AC system (my Cherokees are particularly annoying in that regard- only 1 lb. total system charge) and any loss is more significant. So in some cars, you might notice a loss in cooling after only 5 years. Nothing is WRONG, so topping off is really the only thing you can do.

 

[440Magnum]

Originally Posted By: lairdwd
You also get into the oil compatability issue (if one) in the DIY can. My altima's compressor very clearly calls for PAG 100, yet the DIY cans contain ester or (what I think is) POE. Compatable? I think not.



Compatible, but not optimum. POE and PAG mix just fine, but their specific lubrication properties are a bit different. POE is more tolerant of chlorine residues (say from a conversion to R-134a from R-12), but isn't quite as good a lubricant. OTOH, PAG is very intolerant of moisture and chlorine, but in a pristine system its a bit better lubricant. There are also different viscosities of PAG, POE, and mineral oil used in R-12 systems. 100 is pretty much the norm for the vast majority of cars, but some specific systems specify other vis. oils, probably due to things like variable displacement compressors.

But yes, you really shouldn't ever grab one of the cans that is a witch's brew of lubricants, sealants, "conditioners" and R-134a (see my previous post).

 

[rshaw125]

I had an old van that would lose some freon if the winter was very cold. I would top it off in the spring. I knew if it needed some by checking the temp coming out of the dash vent. Did that for over 5 summers. It would blow 45 degrees all summer after the top up.

 

[Drew99GT]

Originally Posted By: rshaw125
I had an old van that would lose some freon if the winter was very cold. I would top it off in the spring. I knew if it needed some by checking the temp coming out of the dash vent. Did that for over 5 summers. It would blow 45 degrees all summer after the top up.


I'm in the same situation. The key I've found is, it's better to be a bit on the undercharged side than to overcharge the heck out of it. When I need to top my system off after a couple years, since it'll lose several ounces by then, I charge it on a hot day and measure everything at 2,000 rpms and shoot for 50 degree vent temps. As soon as the low side psi goes into the green on the gauge and the air is getting cold, STOP and walk away.

Before I knew what I was doing, I recharged my system on about a 70 degree day and got it at about 45 psi on the low side, and when ambient temps got into the 90s, the pressure inside the system was so high it was tripping the high pressure shutoff.

Before you think your system needs more refrigerant, stick a thermometer in the dash, put the rpms at 2,000 with the windows down, and measure the temps. If you're getting 50 degrees or colder, everything is fine.

 

[Craig in Canada]

Originally Posted By: Drew99GT

Before you think your system needs more refrigerant, stick a thermometer in the dash, put the rpms at 2,000 with the windows down, and measure the temps. If you're getting 50 degrees or colder, everything is fine.


...with the fan set to MAX (important point).

 

[friendly_jacek]

I have a freon detection gauge and tested it on my cars. There is a slow freon leak from the Schroeder ports in both low milage Toyota cars I own. Thus, refrigerant boost is a must in older cars. I plan to check pressures in the older car soon before the worst summer heat starts.

I wish there was a way to tighten the Schroeder ports.

 

[bdcardinal]

Originally Posted By: friendly_jacek
I have a freon detection gauge and tested it on my cars. There is a slow freon leak from the Schroeder ports in both low milage Toyota cars I own. Thus, refrigerant boost is a must in older cars. I plan to check pressures in the older car soon before the worst summer heat starts.

I wish there was a way to tighten the Schroeder ports.


You do realize you can buy replacement valves right? If it were me I would repair the system for a couple bucks vs. adding R134a every few months.

 

[xxch4osxx]

I think they are called Schrader valves, and yes, they are easily replaceable with the right tools.

 

[Chris142]

If you don't suck the refrigerant out , vacuum and refill you really don't know how much to add. A guy that's good with gauges can get reasonably close.

The proper way is to start with an empty and vacuumed system.

 

[Craig in Canada]

Originally Posted By: xxch4osxx
I think they are called Schrader valves, and yes, they are easily replaceable with the right tools.


Replacement doesn't require special tools. Replacement without losing the charge does

 

[lairdwd]

Originally Posted By: Chris142
If you don't suck the refrigerant out , vacuum and refill you really don't know how much to add. A guy that's good with gauges can get reasonably close.

The proper way is to start with an empty and vacuumed system.


Agree. If the diagnostics checks out on the gauges, and it looks like it can hold a vacuum without leaking, I'll bring it to an A/C guy for a complete dischage, vacuum, reload of PAG 46 and r134a. If not, then oh well, gave it a good try.

 

[mechtech2]

Car AC systems DO have a range .
But R134a should not be over filled - more is not better.

 

[friendly_jacek]

Thanks for advice, I will look it up.
The leak is minimal as the sensor I have is super sensitive. The cars have several years and AC still works fine. But, like I said, it's probably time to check the pressure.

 

[440Magnum]

Originally Posted By: friendly_jacek
I have a freon detection gauge and tested it on my cars. There is a slow freon leak from the Schroeder ports in both low milage Toyota cars I own. Thus, refrigerant boost is a must in older cars. I plan to check pressures in the older car soon before the worst summer heat starts.

I wish there was a way to tighten the Schroeder ports.



There is.... And you can replace the schrader valve cores themselves, just like on a tire. AC Schrader valves are just like tire stem valves, except some versions are a bigger diameter. An AC shop or the AC section of most auto parts stores will have a schrader valve tool you can tighten the core in its housing with, but if the schrader valve core itself is leaking you can only replace it with the system discharged.

 

[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.

 

[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.