A/C recharging with cans, How do you tell when they're empty?

[WH23G3G]

I've always had the convience of a shop machine to recharge an A/C system. I've never recharged with cans alone, until now. I've converted one of my old cars into a 134a system, with all new barrier hoses, drier, inline filter, flushed, repaired evaporator, and condenser, and new Sanden SD508 compressor. I added 2 ounces of oil into the compressor, the evaporator, and drier, and one into the condenser. It was an add on system installed back in 1978, so I was not able to find total refill capacity. I was told 7-9 ounces should be adequate. I vacuumed the system down for at least 30 minutes, no leaks were indicated. Then to recharge I used one of those dispensing guns with the trigger and the colored gauge on it. After a few minutes of pressing down the trigger with one can attached. Nothing was going on, so I thought maybe that can was empty since it was cold, so then I tried another one, after 2-3 minutes of squeezing the trigger I thought it was at least partially filled. But no change in air temp. When I removed the cans from the gun, they still had freon shooting out, so obviously I didn't get it all out. Good thing though, because I realized there was 2 ounces of oil in each can. So if any oil got in then I'm still within the 7-8 ounce range. How do you tell if the can is empty? What's best dispensing mechanism a home mechanic can use?

[Steve P.]

I watch a buddy doing AC/ repairs often. Once the repair is made and oil added to the system, he vac.s the system for about 10 minutes. Then shuts the manifold valve and waits a while to make sure it holds a vacuum. If it does, he then fires up the vac. pump and opens the valve. Most times he will vacuum a system that he opened up for more than an hour. He doesn't need to as he has a large volume pump, but better safe than sorry. Then he uses a plastic CAN PIERCING and holding tool. Attaches it to the manifold in place of the pump line. He by-passes the LOW PRESSURE switch and fires up the engine. Make sure you put the fan on high and on MAX AIR.  Open the valve and let the freon fly.

You can tell when the can is empty by it's weight.. Also if you shake it up and down a few times when you think it's empty you may feel some liquid. Give the throttle a few hundred more rpm and then shut the manifold valve. Release the spent can. You should get a short little blast from a spent can. NOT LONG...  Add as many cans as the system calls for.. 

When all the freon is in, shut the engine off. Replace AC caps and put the low pressure wires back in place.  Shut the hood and enjoy your AC.   

Hope this helps...

[Chatt69chgr]

Steve-------do you keep the can upright, that is, do you introduce the freon as a gas?  Would think this would be the case since if you inverted the can, the freon would be introduced as a liquid and possibly cause liquid slugging in the compressor.  Also you can assist the freon to vaporize by placing the can in a pan of warm (not hot) water.  And bypassing the lo-pressure switch allows the compressor to run thereby drawing the freon into the system---correct?  Additionally, I think the freon should always be introduced on the lo pressure side.  Plus, one should always wear a face shield in case by some chance, the can were to explode and throw freon into your eyes.

[Steve P.]

Yes,,, we use the can upright and a can pinch/piercing tool at the very bottom on the side.

ALLLLLLLLLLLways put it in on the LOW side....... 

Also correct on running the compressor to draw ALL the freon out of the can.. The can will get noticeably lighter as it empties into your system..

It should be put through a set of gauges and DON'T OVER FILL THE SYSTEM. 134 will run warm if too much is put in... R-12 is more forgiving..


Hope this helps..

[WH23G3G]

I rechecked the system pressure today and when I started it was low on the low pressure side so I started to add one can. It quickly jumped up too high at about 80psi with the A/C compressor on and the fan blowing high. The High pressure side was low at about the same. I checked the drier and saw that it was flowing with very tiny clusters of bubbles, the bubbles weren't very noticeable, but you could tell because it wasn't just straight stream of liquid. It still felt like the can's weren't emptying into the low side at all. I still believe I have at least a can and a half unused. It takes a little over 2.00lbs. I figure that I actually combined with the three different cans I've tried, I've got maybe a total of one can in. The clutch is engaging, on this system it runs constantly, and the compressor doesn't make any unusual noises at all, I even got the belt tensioned just right. I checked the expansion valve and it's not freezing up, it's not hot either. The condenser isn't unusually hot either, the low side service fitting gets fairly hot when adding. For some reason it's not sucking any freon in. Everything's new on the system besides the evap and condenser which were flushed and silver soldered for any possible leaks by a radiator repair shop. My only guess is where I messed up is vacuuming down the system. I used the venturi type vacuum pump with my 26 gallon compressor. I vacuumed it down for at least 30 minutes possibly more. It was actually one of the cooler days around too about 84, but humidity is still constantly high. I'm thinking of getting evacuated and vacuumed and recharged again. Is there anything else it could be? If the compressor clutch comes on when you turn the switch on and there's no strange noise coming from it, does that mean it should be working? It was replaced too, it's a Sanden SD508 series.

[Steve P.]

What pressures are you reading after it has been running for more than a minute??

Is anything icing up??

[WH23G3G]

Im reading the hi and low pressures after the system has been running for up to 10 minutes. The high is at 80psi and the low is also at 80psi. So the low is too high and the high is too low. I felt the expansion valve and it's not really even cold, and the drier isn't getting cold, but you can see refrigerant flowing through, with the tiny bubbles, so you can tell its still low. But nothing is icing. When I was adding, the service fitting for the low pressure got hot.

[Steve P.]

That sounds like a bad compressor to me.. I am not a pro by any means. I just help out a buddy that does this allllllllotttttt ...  Last time I saw that the compressor was the culprit.. Matter of fact, my 87' Dodge truck has this problem right now. It has had 2 "H" valves and a new evap. put in. They were replaced as I had to go into the heat/AC box to get out all the oak leaves. I also put a new heater core in it. So of course when I tried to charge the system the compressor was junk...

[WH23G3G]

That was the logical conclusion I came too as well. But if it sucked in some, I was thinking maybe there's still some moisture in the system. I called Sanden tech before I installed the compressor to make sure the amount of oil I was installing was adequate for this compressor. The tag on the compressor stated there was a little in the compressor to keep everything from rusting on the shelf and then I added 2oz of Ester 100. They said that would be enough. I put 2 in the evap, 2 in the drier, and 1 in the condenser. I also installed an inline filter. The compressor was a pain to install, since it's at the bottom of the engine so I want to rule everything else out first. I'm going to see if someone can evacuate completely, vacuum down, and then recharge using the machine I use to have at my old job.

[Steve P.]

Let us know how you make out. I talked to my buddy earlier and he also thinks you have a bad compressor. That's a bit strange though, being new.. It wouldn't be the first time..

I would like to see pics. of your set up.  I want to put AC in my 65' Coronet and am thinking about putting it down low at the fuel pump window. Is that where you put yours?? What did you do for brackets??

Thinking about hanging the alt. from the top water pump mount on the drivers side too... Also going to a late model alternator. One of the high amp mini jobs..  I want to keep the belts as short as I can..

[twilt]

If you are reading 80/80 with the compressor clutch engaged and running, its simply a bad compressor.

[WH23G3G]

Everything works, the drier is getting cold and the clutch is engaging. I had a mechanic look at it today. And it was partly my fault and the shop who installed the service fittings. They installed the low side service fiiting in the discharge side and the high pressure side in the suction hose. So nothing was getting sucked in. So luckily there is service adapters on the back of the compressor where I can install a suction R134A fitting. The mechanic said he would do that, evacuate the system, vacuum it longer, and recharge it, this time in the right valve.

[Steve P.]

whoa... That's the first time I have heard of that!! No wonder the cans felt full ..... They were!!