A/C R134a pressure question - Page 5 - PeachParts Mercedes-Benz Forum

Graplr · #61 06-27-2012, 10:52 AM

Quote:

Originally Posted by eatont9999

I drove home the other day after work and it was 102F OAT and these are the pressures and temps I recorded when I parked the car. Idle = approx 800RPM, low side = 48PSI, high side = 250PSI, 70F at center vent medium fan on auto. Edit: If I increase the RPM, the low side goes down to about 40PSI and the high goes close to 280PSI.

Yesterday it was 105F out and I was getting roughly 66F at the vent during city driving and 62-64F on the highway.

This morning it was 83F and I got roughly 58F at the vent.

Is there anything I can do to get lower vent temps? Do my pressures sound correct? I need a larger delta here because when the car sits in the sun, it gets up to 140F. I need that hot air removed ASAP when I turn on the A/C.

This is with R12? If so something is amiss. I know we visited air flow issues awhile ago, but it sure seems like ambient air is mixing to me. Your pressures seem normal at that temperature (without looking at a chart) so that leads me to believe it still is an airflow issue.

60F while driving is high, especially in 83F. I was able to get under that in my 84SD. Down into the mid 40sF with r134a and lower with R12. My 79 300TD with a York compressor and r134a blows 40F at the vent driving up to 90F (hasn't been any hotter yet while I have been driving. Today is supposed to be 95F though).

eatont9999 · #62 06-27-2012, 11:37 AM

This is with R12, new compressor, new drier, new TxV, flush, evap clean, dashpods replaced and a condenser from an 84 W126 chassis.

The system may be over charged. I put a few more ounces in after I noticed the sight glass was clear. If I had a reclaimer, I would evac and charge it again. I had a leak in the system upon initial charge and that screwed me up on my weight. Not to mention I was rushing due to a thunderstorm that was rolling in.

eatont9999 · #63 06-27-2012, 12:00 PM

I'll have to check my recirc flap again and make sure it is still closing all the way. Aside from that, I'm out of ideas.

Graplr · #64 06-27-2012, 12:57 PM

Quote:

Originally Posted by eatont9999

This is with R12, new compressor, new drier, new TxV, flush, evap clean, dashpods replaced and a condenser from an 84 W126 chassis.

The system may be over charged. I put a few more ounces in after I noticed the sight glass was clear. If I had a reclaimer, I would evac and charge it again. I had a leak in the system upon initial charge and that screwed me up on my weight. Not to mention I was rushing due to a thunderstorm that was rolling in.

Wait, I was thinking r134a pressures. With those pressures, it does seem overcharged. According to this chart- http://www.ackits.com/aacf/ptchart.cfm - 100F you should be 26 on the low side and 220-270 on the high side. I have heard overcharging is worse for performance of the evap than undercharging.

I have an R12 reclaimer but I don't think you want to drive to MN for this.

eatont9999 · #65 06-27-2012, 01:38 PM

Thanks for your reply Graplr. I have to concur with you. I wish I could somehow put that R12 back into the tank but the valve won't allow back filling. Then I don't know if the compressor in the car would actually have the pressure on the high side to liquify the R12 into some other container. Never tried doing it.

I stuck my hand up behind the glove box with the A/C system running and the recirc flap is about 90% closed. My understanding is it that it is normal to have it 10% open so you get fresh air in case of an exhaust leak.

Graplr · #66 06-27-2012, 01:45 PM

Quote:

Originally Posted by eatont9999

Thanks for your reply Graplr. I have to concur with you. I wish I could somehow put that R12 back into the tank but the valve won't allow back filling. Then I don't know if the compressor in the car would actually have the pressure on the high side to liquify the R12 into some other container. Never tried doing it.

I stuck my hand up behind the glove box with the A/C system running and the recirc flap is about 90% closed. My understanding is it that it is normal to have it 10% open so you get fresh air in case of an exhaust leak.

I wouldn't mess with trying to put it in a container other than using a reclaimer. At most you are probably talking about 1 lbs of R12 that will be lost, probably less. Hook up your gauges and with the compressor running and see if you can find a simple way to take the R12 out in a well vented area until you get the pressures noted on the chart above.

It will be, what $15-20 lost? Of course that is money, but if you can get your AC working as should, chalk it up to a small cost for that.

I haven't heard of the 10% flap open thing. I remember reading that occasionally the flap will open to allow fresh air in. IIRC it was every half hour or so but then again that could be for my 210.

vstech · #67 06-27-2012, 01:53 PM

Quote:

Originally Posted by Graplr

I wouldn't mess with trying to put it in a container other than using a reclaimer. At most you are probably talking about 1 lbs of R12 that will be lost, probably less. Hook up your gauges and with the compressor running and see if you can find a simple way to take the R12 out in a well vented area until you get the pressures noted on the chart above.

It will be, what $15-20 lost? Of course that is money, but if you can get your AC working as should, chalk it up to a small cost for that.

I haven't heard of the 10% flap open thing. I remember reading that occasionally the flap will open to allow fresh air in. IIRC it was every half hour or so but then again that could be for my 210.

I'd not post this online... the EPA fine is $50,000.00 and there is a $10,000.00 reward for reporting someone...

vstech · #68 06-27-2012, 01:54 PM

most supply houses will sell a one time use reclaim bag or canister just for this purpose.

eatont9999 · #69 06-27-2012, 02:24 PM

I understand the legal implications of venting R12. I will not go into detail or discuss how I will go about correcting my overcharge situation but I will ask some questions that may or may not be related to the A/C system on my car.

Let's assume I am able to procure an acceptable, empty, container with the proper fittings attached. Could I vacuum it down, attach it to the high side with the car running, open the valve and expect to get liquid refrigerant into the container?

vstech · #70 06-27-2012, 02:26 PM

I'd not start the car... I'd vacuum down the container, then just let the vacuum pull out the gas/liquid needed.
you are likely only a tad over. with the car running, you can dump the charge FAST out the liquid line. in no time at all, the system will be very low! and you'd have to put it back in!

Graplr · #71 06-27-2012, 02:38 PM

Quote:

Originally Posted by vstech

I'd not post this online... the EPA fine is $50,000.00 and there is a $10,000.00 reward for reporting someone...

Post what? I stated he find a simple way to get it out. I didn't tell him how to do anything.

jcyuhn · #72 06-27-2012, 03:40 PM

Quote:

Originally Posted by Graplr

This is with R12? If so something is amiss. I know we visited air flow issues awhile ago, but it sure seems like ambient air is mixing to me. Your pressures seem normal at that temperature (without looking at a chart) so that leads me to believe it still is an airflow issue.

60F while driving is high, especially in 83F. I was able to get under that in my 84SD. Down into the mid 40sF with r134a and lower with R12. My 79 300TD with a York compressor and r134a blows 40F at the vent driving up to 90F (hasn't been any hotter yet while I have been driving. Today is supposed to be 95F though).

Those sound a little bit high compared to what I remember for my 1984 300D here in Dallas, but not really out of line.

One trick on the 123 is to modify the fresh air door. The 123 only uses 80% recirculated air per the factory design, so you are mixing in 20% outside air at 105F and high humidity.

Folks have pulled the glove box and manually disconnected the fresh air flap, moving it to the closed position. In my 123 I replumbed the vacuum system so the fresh air flap closed when the CCU called for recirculate (giving 100% recirculated air) and opened when the CCU called for fresh air. (Normal operation is for the fresh air door to open anytime the climate system is switched on.) The instructions for this simple and easily reversible modification have been floating around on mercedesshop/peachparts for the last 10 years, though I could not find them via a quick google search.

In terms of performance, the modification gave me 5 degree cooler discharge air at highway speeds, plus it lowered the humidity of the discharged air sufficient to give it that "crisp" comfortable feel, as opposed to a slightly soggy feel beforehand. Unfortunately I no longer have a copy of the writeup, nor a 123 climate manual to recreate them.

Air&Road · #73 06-27-2012, 06:10 PM

Quote:

Originally Posted by vstech

I'd not post this online... the EPA fine is $50,000.00 and there is a $10,000.00 reward for reporting someone...

GOOD advice!

eatont9999 · #74 06-27-2012, 09:18 PM

OK fellas. I removed some refrigerant from the system. I'm not exactly sure how much but enough to the point where I did not want to risk undercharging the system. Who knows, maybe I succeeded in screwing that up as well. I have a knack for taking simple projects that hundreds of other people have done with great results the first try and turning it into a 2 month long project. I usually find some stupid little thing that either no one else mentioned or is unique to me that caused my frustration.

Well, I made a little video for y'all to help in visual aid. My sight glass is now intermittantly foamy where as before it was clear all the time. My test drive at 60MPH netted me 59F vent temps where as on the drive home, I was getting about 63-65. Idle is still at 70F. I sprayed the condenser with some water before removing any refrigerant and the temps eventually dropped a few degrees and then went back up. The small (liquid - I think) line on the TxV does not get very hot. I can keep my fingers on it for about 10 seconds before it becomes uncomfortable. When I had R134a, it would burn me if I touched it for half a second. Not sure what to make of that. The other lines on the TxV are cold enough to condensate but not ice up.

Here's the video. Try not to wet yourself when I open the car door!

http://www.youtube.com/watch?v=UpXa9ynbeTo

Graplr · #75 06-27-2012, 11:15 PM

I didn't read anywhere about your flushing procedure (if you did one) or what you used for a vacuum pump and how long you evaced the system. It is possible you didn't get all the moisture out of the system? What oil and how much did you use?

I watched the video and don't get what you are referring to about opening the door.