Sudden loss of AC performance, Monovalve? - Page 2 - PeachParts Mercedes-Benz Forum

Roncallo · #16 05-22-2020, 10:08 PM

Well whatever it is its getting worse Like 64° today. I wasn't able to try my stock 107 because my wife had a list of chores for me to do. But I am leaning towards the monovalve because even the outlet of the heater core is hot which should be being cooled by the evaporator. I even did try to pinch it off but my pinch pliers are really too short for the hoes diameter.

I did order a new monovalve, Its not MTC but a company allegedly as bad. Vollig - Heavy Duty

But who knows, maybe they got this part right.

Roncallo · #17 05-23-2020, 05:24 PM

Results are in for the moment. It is not the monovalve because I completely blocked it off. I took the line off and plugged it. 60° duct temp with the monovalve blocked off.

Interesting results with a stock 560SL this morning. The stock 560SL with R12 charged 3 years ago. I turned it on high blower temp came down to 46°, low blower temp down to 36°. Checked the monovalve hose and it was cool. Turned the heat on full to open the monovalve. Monovalve hose got hot. Tuned the AC back on again high blower, couldn't get the temperature below 54° and about 44° with low blower. Monovalve hose remained reasonably warm. It might have gotten better if I let it run for a while but it takes a long time to cool down that heater core. Apparently monovalves do have some leakage, at least 3 year old ones do.

So the modified 560SL also is a little cooler with the system plugged but not much.

I'm getting a little concerned that possibly I did damage to the system when I installed the aux fan. My first install had the fan spinning backwards canceling out what the radiator fan was doing. I drove the car about 5 miles before I realized something was very wrong. AC would not work at all, coolant temp was running high. High side pressure probably tripped the 390PSI pressure limit, assuming the switch worked. They are new Behr switches but I am able to tell that the fan pressure switch, is supposed to turn on the low speed aux fan at 290PSI is turning it on at 230PSI, so maybe the compressor cutout switch is also off. The system has been compromised ever since I ran with the aux fan backwards.

In any case I will leave the mono valve plugged to take it out of the system until I get this sorted. I will have to wait until my recovery system comes in to do any more with charge.

Diseasel300 · #18 05-23-2020, 08:18 PM

The monovalve is not a perfect seal. It won't leak so much that it hurts the cooling performance to any really noticeable degree. The silver temperature regulator box behind the glove box tends to have capacitors that leaks out electrolyte and cause all sorts of crazy temperature regulation issues as well, sometimes running the heat in any position of the temperature wheel except min cold.

I've seen systems grossly overcharged (my SDL was way overcharged from not paying attention once) running head pressures up to 400PSI and tripping the overpressure switch and they came around just fine once the charge was corrected. If you didn't blow any seals or hoses, you're probably fine.

I still say you're just grossly overcharged.

Roncallo · #19 05-23-2020, 09:30 PM

Quote:

Originally Posted by Diseasel300

The monovalve is not a perfect seal. It won't leak so much that it hurts the cooling performance to any really noticeable degree. The silver temperature regulator box behind the glove box tends to have capacitors that leaks out electrolyte and cause all sorts of crazy temperature regulation issues as well, sometimes running the heat in any position of the temperature wheel except min cold.

I've seen systems grossly overcharged (my SDL was way overcharged from not paying attention once) running head pressures up to 400PSI and tripping the overpressure switch and they came around just fine once the charge was corrected. If you didn't blow any seals or hoses, you're probably fine.

I still say you're just grossly overcharged.

I hope so. Wont know for about a week, but no reason to rush. In the end I will need to know what the proper charge is. So I will have a nice cylinder and scale I can properly weigh with. But I did find the monovalve leakage to have a significant hit on the performance 8° on my stock 560SL is pretty significant. That was one of the last genuine Mercedes monovalves available at the time.

Thanks again touch base in a week or so.

Diseasel300 · #20 05-23-2020, 10:08 PM

Try energizing the monovalve with 12V and see if you have any difference. If you do, the silver box is probably on its way out.

Roncallo · #21 05-24-2020, 12:30 PM

Quote:

Originally Posted by Diseasel300

Try energizing the monovalve with 12V and see if you have any difference. If you do, the silver box is probably on its way out.

I did that on the car in question. No difference, But maybe I should try it on the stock 560SL. I rebuilt that system 3 years ago and that and the evaporator are the only parts I didn't replace.

Diseasel300 · #22 05-24-2020, 12:45 PM

The stock 560SL is the one I was suggesting to try the 12V on. If you see a difference, the silver box is probably the source of the leak, not the monovalve cartridge.

Roncallo · #23 05-24-2020, 11:41 PM

Quote:

Originally Posted by Diseasel300

The stock 560SL is the one I was suggesting to try the 12V on. If you see a difference, the silver box is probably the source of the leak, not the monovalve cartridge.

Of course I went to try this today and it wouldn't act up as it did before duct temp returned to within 2° of where it was before putting the heater on.

It was an 86° day today, I took both 560SL's for a spin and my 2009 F150 to see how the AC performed. These were windows closed (except the stock 560SL) qualitative test just to see how comfortable they were.

All three were taken on a 10 mile round trip along the country roads near me with a few stop lights and generally 50MPH driving. By the end of the 5 mile run where I turned around, each had pretty stable duct temperatures. Unfortunately the stock 560SL needs the back latch adjusted so for the moment I can only run that one top down windows up.

First was the 560SL with the M120 V12. Duct temperatures were 60° to 64°. Usually 60° on the open road and settling to 64° at a light. Comfort was reasonable. Would have liked it to be a little cooler but not bad. So right now ~ 85° is its limit for comfort the way it is. It was also nice to see that in the higher temps today the duct temperature didn't clime higher than what it was at 70° ambient.

Next was the Ford F150 pick up. AC not serviced since new. That fluctuated between 56° to 60°. That was perfect mostly because while 56° to 60° may seem high, the blower puts out about 2 times the volume of the 107.

The stock (R12) 560SL would run about 55° and didn't seem to rise at the lights. That was extremely comfortable with the top down and AC blowing full. Probably a significant penalty on that duct temp with the top down.

I also performed a sub cooling test today. Sub cooling is the way a residential TXV AC system would have its charge set, assuming the TXV is working correctly. Generally you want to see about 10° sub cooling with the typical range being 8° to 17°. This is usually performed in a residential building with the AC system stabilized indoor temperature.

I performed this in the car with windows open, full blower engine at 2000RPM and got 10° sub cooling. I reset the system to thermostatic control, automatic blower. Allowed the temperature to stabilize in the car to simulate just like I was doing a residential test. I ran the car at idle and got 4° sub cooling. Ran at 2000 RPM I got 6° sub cooling.

Seems like reasonable ball park numbers, but who knows, maybe a car need 25° sub cooling because by the time the Freon travels from the condenser through the engine compartment and finally gets to the expansion valve it may pick up enough heat from the engine compartment to be at a reduced level of sub cooling. There is probably a reason Mercedes says to perform testing with the hood closed. Except they don't tell you where to put your gauges when your doing this.

Really without having a manufactures procedure for doing this its a pretty useless test. But it is pointing to under charge. Also the high side pressure port for this system is on the inlet of the condenser, which is not where sub cooling pressure is usually measured. It should be on the outlet of the receiver drier. I can only assume the pressure drop across a parallel flow condenser is small and that the measured sub cooling numbers are slightly high.

The other thing pointing to undercharge is that I never added Freon since I first got the system running with a 42° duct temp. There was an opportunity for me to have had a leak before I got my leak detector. I cant find one now but I did tighten the shrader valves. They weren't loose but I got about 1/4 turn out of them. So honestly I have no idea what in there now.

Well my new recovery tank just came in but I wont see the recovery machine for a week. Tomorrow I go an pick up a bottle of nitrogen to purge out the R410 my brother was using in his recovery machine when it gets here. So hopefully next weekend.

Diseasel300 · #24 05-24-2020, 11:54 PM

For an 85˚ day, you should have a 55˚ vent temp if all the windows and doors are open. Your stock 560 is performing as designed. Your truck needs charging (Fords should be quite cold, even on high fan), and your V12 car needs the charge corrected. It's obvious any input I'm giving (based on considerable experience with A/C systems) is being ignored, so this is my last comment on this thread.

Roncallo · #25 05-25-2020, 01:54 AM

Quote:

Originally Posted by Diseasel300

For an 85˚ day, you should have a 55˚ vent temp if all the windows and doors are open. Your stock 560 is performing as designed. Your truck needs charging (Fords should be quite cold, even on high fan), and your V12 car needs the charge corrected. It's obvious any input I'm giving (based on considerable experience with A/C systems) is being ignored, so this is my last comment on this thread.

I'm sorry, I haven't ignored any of your inputs. I think they have actually been very good. I agree with everything you say above. But I wont dump Freon without the proper means of disposal; and the ability to quantify how much I have. Weather its under or over charged we will find out, but the bottom line is I need to find out what the proper charge is because its not on a label anywhere.

URO Parts Support · #26 05-27-2020, 12:44 PM

Quote:

Originally Posted by Roncallo

I hate to try a new monovalve because the only ones now available are MTC aftermarkets, and I and many others have had a bad experience with.

Quick FYI: Our engineers are currently redesigning our Monovalve Repair Kit 0008350644R, and the improved version should be available in six to nine months. The primary change is adjusting the rubber diaphragm profile a bit for easier movement, and some minor changes to the smaller pieces.

Roncallo · #27 05-28-2020, 01:27 AM

Quote:

Originally Posted by URO Parts Support

Quick FYI: Our engineers are currently redesigning our Monovalve Repair Kit 0008350644R, and the improved version should be available in six to nine months. The primary change is adjusting the rubber diaphragm profile a bit for easier movement, and some minor changes to the smaller pieces.

I hope you do a good job testing it. Please come through for us.

Roncallo · #28 05-29-2020, 01:23 PM

Well, got the recovery system, purged it with Nitrogen, got a new filter for it, changed the oil on my vac pump, did a test of my scale. Then I looked at the new recovery tank I got on e-bay. No DOT specification, no pressure test date. There was neither pressure of vacuum in it. So I requested a return and ordered a Robinair tank. So we wait again.

Don't buy this:

https://www.ebay.com/itm/323857544799

In the mean time, I retook my MAC 609 test. Completely read the study guide. A very worthwhile read. The study guide is available on line for free. The test cost $20.00 to take and anyone should be able to pass the test if they read the study guide. But a lot of new interesting details were added including stuff for the new R1234 type refrigerant. Two of the more interesting things I found were how to recover 95+% of the Freon and a little mention on how much a service lines hold. They just give you a short heads up that a 6' service line can fold up to 2oz of R134. I always suspected something like that but never saw it published. That also means that my stock 107 is probably undercharged, since the required charge is 1Kg = 35.3oz and I put in 3 12oz cans and purged the line each time and then disconnected both the high and low side lines. R12 lines are not like R134a lines, they spray out Freon all over the place when you disconnect them. Its always been one of the reasons I like to charge with a 30# cylinder. But I'm not about to crack open one of my last remaining 12oz cans of R12 to put in 3 oz.

So again I weight. Hopefully the new tank will be here by Wednesday at which time I will have 3 days of 85°+ weather.

Roncallo · #29 06-04-2020, 10:54 PM

Well the results are in. The new recovery tank came in today and I recovered 11 oz of the original 36 oz of Freon I put in. So that meant that at some time or possibly still I had or have a leak. The only thing I can think of is that there is a good possibility I left the gauges hooked up for the week that I was waiting for my fan controller. At that time I did not have a leak detector. I have one now and cant find a leak but I think we will now for sure in about 2 weeks.

So the task still remained as to finding the correct charge I should be using for this system. So while I was down I did a little calculation of the volumes of the original and replacement condensers. It turns out that the new condenser is ~ 5% less volume than the old serpentine condenser. As a system that account for about 2% less for the entire system. Therefor using the 85% charge typically used for going from R12 to R134 I cam out with 29.4 oz.

So with 88 to 89°F ambient temps I slowly approached 30oz. At 24 oz Most of the bubbles in the sight glass disappeared. The ambient temp duct temp, and pressures were all recorded with stabilized readings at 2000RPM.

At 24 oz - Ambient = 87° Pressures 245/16 PSI, Duct Temp 55°
At 28 oz - Ambient = 89° Pressures 250/16 PSI, Duct Temp 54°
At 30 oz - Ambient = 89° Pressures 255/16 PSI, Duct Temp 54°

I stopped at 30 oz since nothing appeared to be changing and it was in line with the estimated correct amount.

Attached is the MB performance chart for the 560SL running R12. While the performance of this system is nothing to write home about, I am clearly beating the stock 560SL using R134. And that would be consistent with the 42° duct temperature I measured when it was only 70° ambient.

So what remains is do I have a leak or not. I will report back in a week or so.

vwnate1 · #30 06-05-2020, 02:57 AM

You jogged my memory : Thursday I took my Foster boys all over Los Angeles in my Rich upgraded '82 240D ~ in Woodland Hills it was 103* F and the dash vent read 60* F on the freeway at 60 MPH .

In North Hollywood I encountered 106* F and the dash vent was 58* F .

In Pasadena it was 104*F and the dash vent was 56* F for a short time then crept up to 60 ~ 62* F so I guess I'm good to go, a 40* F TEMPERATURE DROP is good enough for me .