Hello: I have a dual R12/R134a a/c recovery/recharge unit. I'm trying to charge my 1990 300SE with virgin 134 after recovering what was in the system and then pulling a vacuum on it.

I cannot get the charge into the vehicle as the pressures are too high. I've found that the pressures are high in the hoses while they aren't even hooked up to the car's a/c system. I have had the a/c unit remove the pressure from the hoses and then I hooked them up to the vehicle. However, only approximately 7 ounces of refrigerant gets sucked into the system before the pressure builds again and inhibits more refrigerant from being drawn into the vehicle's a/c system.

Either I'm doing something wrong or there's something wrong with my recovery/recharge unit.

If someone with experience using auto a/c recovery/recharge units can walk me through this I would appreciate it. I would not mind paying for a phone consultation. I can send payment via PayPal.

Please send me a PM or post hereon if you are able to help.

Thank you.

Close the high side valve and charge into the low side. It should just suck it right in if you are charging with the enigne running.

A lot of new machines are set up to charge into the high side but as you have found out, that is not always the best way. Ideally you pull a vacuum and that vacuum will pull in all of the required refrigerant. Charging into the high side is ok if that works out. If it doesn't then compressor operation just tries to push it back into the machine which sounds like what you are experiencing. So just charge it into the low side. Even if the machine is set up to charge the high side it will do if from the low side.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

After talking with you I remembered you do want to close the high side valve on your machine when charging (you should be able to leave the high side valve at the charge nozzle open). Sorry about that.

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Jim

Well, it's obviously a learning process for me, but I'm getting there.

Here's what happened: I closed both valves and hooked them up to the high and low sides. Then I opened them and recovered the refrigerant. That went well. I then pulled a vacuum on it for 45 minutes. That went well.

With the car off I then set the unit to dispense the correct amount of refrigerant. Twenty two ounces were sucked right into the system. Very nice at this point. I still need 16.75 ounces to go in. Well, at this point I get an error code telling me the pressure is too high. So I shut it down.

I wanted to call it a night so I closed both valves at the hose ends and detached the low side from the car. I went to detach the high side, but it's way too hot! So I'm letting it sit for a while then I'll take it off and start back up in the morning.

Now, since I had that high side hose open when I was charging the system, do I need to start over again with a recovery, vacuum and charge? Or, do I pick up where I left off?

Thank you for your help.

Thank you for your response.

It seems you hit the nail on the head. I actually had two problems. I wasn't operating the valves correctly and I didn't close the high side when I was charging the system.

I have valves at the machine on mine and when ever I charge I charge through the low side valve (the high side valve is closed on the machine) and a "charge" valve that I throttle to control refrigerant going into the car (the valves at the ends of the hoses remain open the whole time). You should have enough refrigerant in the car to satisfy the low pressure switch so if you did not get to your target charge amount then you can run the car with the a/c on (the compressor should run at this point) and the low side pressure should come down allowing you to throttle the remaining amount of regrigerant into the car.

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Jim

It seems the only way to close the high side on my machine is at the end of the hose where it attaches to the vehicle. I guess it doesn't matter as long as it's closed somewhere.

And yes, enough refrigerant was introduced into the system to satisfy the low pressure switch which allowed the compressor to come on. So, I'm in pretty good shape right now.

Tomorrow morning I will try to get the rest of the refrigerant in. I'll report back here with my progress.

Thank you once again. I appreciate your help.

Glad to help. You may want to go back and evacuate/vacuum again to start from scratch. I don't like to disconnect my machine until all the freon is in the car based on actual weight. If you don't want to go back through that procedure then you can run a vacuum on the low side hose before you open the valve at the end of the hose. Sounds like you are about to get it.

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Jim

Yes, before I read your last post I was just thinking that I should do a complete recovery/recharge again. It's certainly good practice for me. I'm feeling pretty good about it now.

I'll report back tomorrow.

Thank you.

Success!

With step-by-step help from engatwork via the telephone, I was able to completely charge my vehicle's a/c system this morning. Opening and closing the valves on the recovery/recharge unit at the correct times was key.

I was able to go through all of the steps, and after the vacuum was pulled for 45 minutes all 38 ounces of refrigerant were sucked right into the system. I didn't even have to start the car to do it.

So, a HUGE thank you to engatwork for his help.

And thank you to duxthe1 for his post that helped confirm where my errors were.

That's what we're here for.

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Jim