A Truly Simple A/C Question
 

I need to top off the R-12 in my A/C. I have the small 14 oz cans of R12, a top tapper and charging hose. I know to feed GAS into the low-side while watching the sight glass for bubble reduction. What I don't know is the proper way to hook up the charging hose. Do I tap the can, vent off a little R12 and quickly attach to the low side connection? Is there a better way to purge the charging line? I am trying to avoid the introduction of non-compressible gasses into the system.
Thanks.
got my 609 too :-)

Personally, I would never add freon without being able to monitor both high and low side pressures. If you get too much pressure in the high side hose it can explode, so it's a very good idea to know what's going on in your system. The method you describe is basically the method that I use with my manifold and gauges, but with the added step of bleeding two more lines. I like to thread the fitting into the low side service valve (not enough to seat it) before opening the valve on the can tap. That way I can seal the line quickly. Unless you're pulling a vacuum on the system, I don't know of a better way. However, this is an old-fashioned way of doing it, and someone may have since come up with a better way.

No way to do it with just a can tapper.

With hoses and a set manifold guages, it works as follows. Close both hi & low valves. Attach both hi & low side hoses. Crack open the low side valve, allowing a slow flow of refrigerant up the low side hose, into the manifold, and down the charging hose to the can tapper. After a few seconds of allowing the refrigerant flow to push the air out of the hoses, tap the can.

There are other procedures as well.

Can't do this with your setup because you don't have a shutoff valve to control refrigerant flow though the hose.

- JimY

"I am trying to avoid the introduction of non-compressible gasses into the system."
An admirable Goal...

That starting the R12 through the line with it attached but on lightly....and then tightening it was the old style way of doing it...
I think they have new hoses ... which I don't have yet... which are designed to either avoid that or minimize the amout of R12 vented to accomplish that goal...
But I am surprised that that was not covered in the 609 test.. ???????

I agree that you are trying to do this with less tools than is required to do it properly or safely...
You can run your system many many ounces lower than the max charge with few bad results compared to even ONE ounce over charged.. that really works against the whole AC gas/liquid change in pressure/soak up heat theory...

Something else I have heard is an overcharge can bend, break or wear the piston vanes inside the compressor and possibly the shaft seal. especially with R134a. high side monitors the pressure comming out of the compressor and really alerts you of an over charge. Sight glass can be misleading.

Go/log on to Harbour Freight tools; Nice new R12 gauge sets $39, R134A sets $49.

That is good info about the hose purge, I wish my former indy tech did this ($100 quote for evac/charge with my R12and my gauges) Along with his upside down discharge can (liquid) into low side, shotty 15 min vacuum. I trusted this guy until i watched him and got educated here. Now he says i have a bad compressor, I think he did it but can not prove it, he was quick to reclaim 1.65 lbs of my R12 and says it is too contaiminated to reuse. btw I paid him nothing and wont go back.

DIY forever on everything is my new motto.

About 1972 I busted two rebuilt compressor in one day putting liquid refrigerant into the suction side of the compressor... PING went the reed valves... but I was young ... will let yall fill in the rest of the sentence....

For a 'pro' that guy is a real loser... you are on the right track....

I plan to buy a good full charging set for R12. I see 30lbs going for maybe 400 and in truth once I'm better equipped, pump, good charging set etc both my W123's are getting treated to re-built AC's. I know the systems are basically OK but leaky and hope to tear apart and fix at least one this summer. I didn't see the r12 hoses at HF but will look again. They are on-line too. I think I'll do that instead of the single charging hose. The car in question isn't an MB; the A/C still freezes you out after 16 years. I've never even removed the caps on the lines. There's a steady stream of bubbles when at full load so I wanted to add a couple of OZ's to keep everything working. My goal is to see the amount of bubbles drop a little, not go away completely.

" My goal is to see the amount of bubbles drop a little, not go away completely."

Good...there are many warnings that even at correct charge under some situations you will still have some bubbles... so if someone uses ' getting rid of the bubbles' as the criteria they will most probably have overcharged their system.... very bad for performance....

:confused: Non-compressable ? ..I think all gases are compressable.....
You don't mean...non-condensable do you ? ;)


_

I think that is short hand in the industry for non compressible into liquid AT the Temperatures and Pressures available inside the AC system.....the working parameters of the compressor .....

I didn't find much of the information in the 609 study manual useful for actually working on A/C. You need to know what color cylinders different refrigerants are stored in, a bit about the ozone depletion theory, flammable refrigerants are against federal law in automotive A/Cs, cross-contamination of refrigerants is bad, etc. Nothing in the test actually tests ability to do A/C work, or knowledge of how A/C functions. Remember, we're dealing with the federal government here, so don't expect it to make too much sense :rolleyes:

Well, that makes sense... they are mainly charged with making sure AC guys know about the ozone deal.... and federal regulations....

Here you go: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=1504

May I add another wrinkle to this question? If one is using a vaccuum pump to draw down the system after a part replacement, both valves are open on the gauge set during the vaccuum. After the process is done, then both valves on the gauge set are closed, and the pump is shut off and disconnected. May I assume that purging the fill line at the gauge set after attaching the can of R134 will suffice? Since the low side line is in a vaccuum state, would it be unnecessary to somehow purge it also?

Thanks in advance...