Need help with a/c recovery/recharge unit operation
 

Hello: I purchased an R134a/R12 dual refrigerant recovery and recharge unit. I just changed the a/c pressure switch and drier in my car. The machine pulled and held a vacuum on the system. So, all of that is fine. However, I can't get the freon into my a/c system.

I'm using R134a because it had already been converted. I just want the a/c working now and will convert back to R12 later. The problem now is the "pressurizing tank" light on the unit keeps flashing. The manual states that I should start the car and turn on the a/c because there is a pressure difference that needs to be corrected. I did that and it is still the same.

The a/c compressor in m car is not turning on because there is no refrigerant in the system. It seems like I'm almost there, but I need that little push from the in house experts.

Thank you for your help.

I think I'm familiar with that unit. It will need to see 100PSI in the tank before it will charge. When it is "pressurizing tank" it is actually warming the tank which raises the pressure in the tank assuming it has sufficient refrigerant. It can take several minutes before pressure comes up. In addition there are valves inline and at the tank that need to be opened before use and ideally closed after every use. If the valves are closed it won't see the pressure and won't charge.

Thanks for your response.

I pulled a vacuum on the car's a/c system and immediately set the unit to charge it with virgin R134. Seven ounces were sucked in rather quickly, then nothing. The virgin cylinder seemed to be heated pretty good. I don't know how hot it should get before the pressure is high enough. The manual says it could take 10 minutes, but it was longer than that.

The car's compressor doesn't seem to be turning on. The clutch certainly isn't turning, but I can turn it by hand. Does the car's compressor need to be running in order to draw in more of the refrigerant? If so, how do I get it to run?

I vacuumed and tried to charge the system again. The low side reads 105 and the high side is 110. The compressor is still not on. Six ounces of refrigerant were sucked into the system before it stopped. Any ideas?

search posts by larry bible.... he seems to know the systems...

there's a way to jump the a/c compressor to have it start up....

from mb doc:

if you remove the klima & use a jumper wire between circuit 15(power) & 87(compressor) the compressor has to run....

Those circuits are marked on the relay..& are marked 5 & 7 on the electrical connector.

That test will allow you to decide if the compressor is good or if you are having "klima" control problems.
__________________

Thanks Lee. I was just doing that when I came in and saw your post. I jumped the pressure switch and the compressor turns on and the clutch engages. However, there still seems to be a pressure gradient. Maybe now that I know how to turn on the compressor I should evacuate the system, pull a vaccum and try to charge it again.

Oh, and I've read so many related a/c posts that my head hurts.

There's still a problem with the pressure as the "pressurizing tank" light on the a/c recovery/recharge unit continues flashing. The refrigerant is just not getting drawn into the car's a/c system. I didn't perform another evacuate and vacuum cycle after I got the car's compressor to turn on. I don't know if that's where my problem is.

So far only 8 ounces of refrigerant have gone in. I don't want to run the car's compressor too long without a sufficient charge.

Does anyone have any other recommendations?

what kind of air do you have when you run the compressor.....??? cool? i think the systems don't take much more than a can and a half or so..

i don't want to lead you down the wrong path...but wondering if you have a stuck expansion valve.

It doesn't feel cool yet. The system was totally empty as I evacuated it and drew a good vacuum on it for a while. I changed the switches and the drier. The specs call for 38.75 ounces of R134a in the system. So, 8 ounces isn't going to do much. I'm not negating your theory about the expansion valve, I'm just stating some facts.

Thank you.

ok.... the other thing is..anytime i have added refrigerant.. i have someone step on the gas and get the rpms up to 1500

Thank you.
I just tried that. Nothing.

This is what is written in the manual for the a/c recovery/recharge unit:

"In some instances a differential condition may occur. This happens when there is a pressure balance between the unit and the vehicle air conditioning system. If a differential condition is reached, the PRESSURIZING TANK light will begin flashing. To correct a differential condition, turn the engine on, start the vehicle air conditioning system and press START/STOP OPERATION on the left hand panel."

Well, I've done that and it still does not draw refrigerant into the system. I jumped the pressure switch to get the compressor to turn on and the clutch spins freely while it's on. It's not intermittent.

I really need to know how to get that pressure gradient taken care of. Do I need to evacuate the system and draw a vacuum again now that I have the compressor running?

with the equipment you have it should be a piece of cake.

headed to port st lucie to look at a 95 e320 coupe... will check back in later

So, you're saying I'm not the sharpest tool in the shed? If so, I'm sure you're mistaken as my wife says I pretty much know everything. Well, except how to operate an auto a/c recovery/recharge unit.

Well, I've given up until I can get some definitive answers. I evacuated the system and pulled a vacuum on it again. I tried to charge it with the car running and the compressor on. The low side went up to 130 this time and the high side was at 105 or so. It only drew in 7 ounces. I shut it down because it just seemed the low side pressure was too high.

I had the same issue when I charged my 260E. It would not pull in anything more than the first can. In the end, I had to run the car at 2000rpm with the can in hot water for it do it. Have you tried that?

I am not sure why your low side is higher than the high side though. Possible blockage at expansion valve?

Did you put in correct amount of oil to correct for replacement of RD? (not your cause, but side Q)

Thanks for your reply.

The a/c unit has a "blanket" which heats the virgin cylinder, so there's no issue with a can freezing. The cylinder is pretty well heated.

The low side pressure seems to be my problem right now. Before my system lost enough refrigerant for the compressor to shut of it was in good operating condition. Looking back at it now, there were moments when it was intermittent, but that was more than likely because the refrigerant was slowly being lost via the pressure switch.

Could the loss of freon have caused a problem wth the expansion valve?

Yes, I replaced the oil.

Thank you.

I'm going to keep throwings things out there until something sticks. So, can the drier be part of the problem? I started this whole process last evening. I put a new drier in at that time, but the system was not left under vacuum overnight. I haven't opened the system after that drier was installed, but hasn't it been accumulating moisture all of this time?

If I should change the drier again I will as I have another new one. If I have to pull a longer vacuum on the system before attempting to charge it again I can do that also.

I just need some ideas here.

Thank you.

Recovery tank pressure is not what will keep it from charging from the tank. There is a float sensor in the tank and it will not release refrigerant from the tank until enough is in the tank for a charge. It will take several recoveries after tank preparation before you can charge from it.

Hope this helps.

Thanks for your help.

However, I do not want to charge from the recovery tank. I want to charge from the virgin tank of R134. There's a mode selector button on the unit which lets me choose "Charge Virgin"... So, that's what I've been attempting to do.

I went out this morning and pulled a vacuum on the system for an hour. Immediately after that hour was up I set the unit to charge the car's a/c system from the virgin tank of R134. This time it sucked in 1 pound of refrigerant. The low side pressure was 30 and the high was 200. The ambient temp was 85 degrees. The low pressure was actually all over the place at times. It went all the way up to 150 and dropped back down to between 30 and 40 rather quickly a number of times. I don't know if that's because of the pump going on and off or what.

If I shut the car off the low side goes to 70 and the high to 160. With the engine revving the low drops to 15 and the high up to 200. I can't get any more refrigerant in right now. I'm obviously getting there, but need that little push in the way of information as to what my next step should be.

The compressor turns on by itself now since there's a lb of R134 in the system. The vents blow cool, but not cold. I have to put 1 lb 6 oz more of refrigerant into the car.

Any help is appreciated.

revving at 1500 ...you need to get in the upper 30's for low side...then you will have cool air... high side is almost there....

congratulations on the progress made.

Hey Lee: I had someone revving it up between 1500 and 2000 rpm. It just wouldn't draw in any more.

maybe try later in the day..... that seems to be working for you...

all kidding aside... i just don't have any other answers.... or the one i give you ....you may not like/

take it to an a/c guy and let him show you the final trick if there is one....

i think the key is that you are holding vaccuum and don't have leaks....

Yeah, I know I can always take it to someone tomorrow. However, the guys I've dealt with here don't want me hanging around while they do anything. They don't want to educate me so I can do it myself. So, just letting someone else do it doesn't get me the answers I need. We've all been begginers at some time. I just need to find out what the proper procedure is and I can take it from there.

Pulling the 1 hour vacuum seemed to have made the difference. I don't know. Maybe it was coincidental. I'll keep my eyes on this post today waiting for more answers.

Thanks for your help.

you are probably trying to draw gas off the top of the tank instead of charging carefully with liquid where the gas pressure is used to push the liquid in.[100psi gas pressure in tank and 30psi pressure on low side if you open valve it will flow to the lowest pressure]

Hello: Thanks for your reply. I really don't know what you're referring to. The recovery/recharge unit I have can be set to do the charge automatically after the system is evacuated/vacuumed, or each function can be manually set one at a time. I tried it both ways.

The fact is, I finally got a complete charge of 39 ounces of R134 into my 1990 300SE. It's obviously a learning process for me. I held a vacuum on the system for one hour. Then, I immediately set the system to charge the 39 ounces of R134. The car's a/c system drew in 16 ounces in short order then stopped. So, I disconnected the hoses, evacuated them and hooked them up again. The system drew in another 7 ounces. I did that two more times (9 ounces, then 7 ounces) until the full 39 ounces were transferred into the car's a/c system.

I still don't know what I was doing wrong. I guess I'll figure it out one of these days.

The R134a provides reasonable cooling when it's not terribly hot here in Southern Florida. However, when the ambient temperature is above 85 degress, the fan has to be constantly on high or the cabin will become unbearable. I certainly want to convert the system back to R12 so that it can run as it was meant to. I'll start purchasing parts to do that soon.

strictly local driving in PBG will kill you....too much traffic there...

congratulatoins.

Too much traffic? Stop it! I've been in traffic. New York, LA and Miami have traffic. This is nothing.