420SEL AC Pressures
 

Hey everyone,

With this recent warm up, I've decided to go through the cars and check AC systems. Much to my surprise my 190E's works, in the past it had leaked out and stopped working. However my 420SEL's is not working so well.

The compressor kicks on, I put the manifold on it and got 60 PSI static pressure, with engine on readings with the aux fan on and ambient temp at front of radiator about 80F:

According to charts at 80F ambient one should see ~18 Low, 170-210 High.

I saw,

At Idle:
3 Psi Low, 100 Psi High

At 1500 RPM:
0 Psi Low, 100 Psi High

So I felt that the charge was low, so I grabbed a can of R12 and started charging.

Idle:
20 low, 165 High

1500:
10 low, 165 High

I checked the gauge I put in the center vents, it was hitting high 60s. So I thought it was still undercharged a bit. I think I overcharged a bit, I ended up with:

Idle:
30 low, 175 High

1500:
17 Low, 180 High

That's a question I have about these charts are these pressures at idle or at a higher rpm?

What do you guys think?


EDIT: After a short trip (~40mph speed) I achieved about 55F at the center vents with my cheapo dial thermometer.
EDIT: Did another run on the freeway, used my DMM with temp sensor, lowest was 56F. Sat between 56-58F.

Not a clue. I'd have to get some dye and put it in there and to find out. The compressor is relatively new, we had it replaced 2 years ago. So I'd hope the o-rings engine side were all replaced.

I ran my 190E and its AC is substantially better. I got 34F at the center vents with the fan on low. The 420SEL only was able to muster 58F under the same conditions.

The 190E is running ES-12A whereas the 420SEL has R12.

How does the sight glass look? From what I recall in the FSM the pressures should be higher on an 80* day.

EDIT: nevermind, according to this it sounds like you have it about perfect.

http://www.peachparts.com/shopforum/...1&d=1332371825

-J

I'll have to take a look at the glass.

Are you talking about the low side ? high side? at idle? at 1500?

See my edited post. I thought the low and high side both seemed low at 1500 RPM.

So perhaps its still undercharged?

With R12 you should be able to look at the sight glass. There should be few to no bubbles.

-J

Make sure you do not have a vacuum proublem with one of the controle units for the fresh air and heater door, I had that trouble with my wifes 420 sel and could not cool the car very well. JNT

I looked at the sight glass, I saw white stuff rolling around in there, didnt really see any bubbles though. Just white stuff.

Hmm. I havent checked into any of that yet but I think the re-circulation isnt functioning properly. At least I cannot hear it engage. In the 190E its very obvious.

sight glass(white stuff)
 

that white stuff is air swirling around if you put more in and look at the glass you will sea it dissapate you shoul have just an ocational buble.

Ya, white foam = bubbles.

While you're doing your test you should use a hose to wet the condenser.

-J

Hmm so you're saying I should put more R12 in the system and observe the sight glass while I'm doing so?

Based on that chart I get:

Outside Temp 80F = 26.6C
2 Bar Low = 29 PSI Low
22 Bar High = 319 Psi High

That high side seems...high.

Ok lets see if I can help you on this, the first thing I think of is a restriction to flow if I get higher than normal reading on the high side, But first I have to no if the system is over charged. This is when I bring the sight glass into play as I charge the system I look for very slow or even no movement in the glass, of course it is moving along at its normal flow rate but as the airated bubles go away it looks like things are standing still. Now high pressure could also come from contaminated freon, water the dryer, may be in need of replacement. I hope I have helped you a little, I know you have given me great info. By the way I converted all of our units to freez12 it has propane in it and not every one carries it but it sure is cheaper than the old 12. JNT

http://www.ackits.com/aacf/ptchart.cfm

Test these at high idle.

Make sure you have no bad vac pods, a dead center pod keeps the defroster pod from fully closing which shuts the center vent flapper door...

Freeze 12 sucks in these cars in the city. Works fine freeway. Cost of R12 is not bad at all if you look hard and buy it off season.

now realy, if you do a great deal of city you are correct it is not so great, but he lives in the north woods not like u and I we live in the heat belt.

I've got a few cans of R12, they were 20$/each. Originally bought them for the SD.

I use the ES-12A in the 190E because I'm cheap and there was a leak for a while. So far I've had this ES-12A stuff in for more than a year and its still cold. I mean 34F at the center vent (80F ambient) is good enough by me.

I popped a bottle of wallyworld stove propane in mine a month ago and am a VERY happy camper! It sucked it in in about a minute or two. Ive been wanting to do this for a few years and finally thought oh what the hell and now I am SOLD 100%. it gets colder quicker and the head pressure is a lot lower!.....I have used freeze 12 also in the past and give that one a thumbs up. If your a cheapo/rebel like me and a dupont conspiracy theorist then the propane is the best stick it up yer butt, i've seen in a long time LOL......its almost as much fun as burning 100% two stroke oil in my SDL at 50cents a quart when its on sale!

I was talking with Hit Man X earlier about the main air flap maybe not working properly. I tore into the area today and found that it stays shut no matter what mode I have it set for. I've yet to find my MityVac but when I do I'll confirm that the pods are dead.

So the question now is how much does defective pods diminish my cooling capacity? Is 56-58F at the center vents on low fan speed acceptable for a W126? I know that its not quite fair to compare the center vent reading on my 190E to the 420SEL because the 190E's evaporator is right on the other side of the center vents and the 420's is elsewhere.

I found this in the FSM that might be helpful for others:
http://i.imgur.com/55J7yl.jpg

that could be a reason for temp. being less than you wish for but not restriction or high pressure on the high side, adding another can to clear up the bubles will not bring down the pressure. how old is the exspansion valve? it has a very small transfer arrea and even slite crud can plug it enough to cause high readings. then again if it is the Orifise type it may have what is called the black death, at whitch time it is flush time to clear out those contaminets. Good luck with it. OH yes before I go If your ambient temps are from 75 to 85 your high side pressure should run from 160 to 220 psi Memory (JNT)

My high side pressure is only about 160-180 or so which is on the lower side of the scale for that ambient temperature.

Disconnect the arms from the pods and wedge the door open. You will then be recirculating the cooled air making it colder in the cabin as opposed to cooling ambient air.



This is also causing a vac leak under the hood. So once you repair the system, recheck your CO.

Replacing the three on behind the glovebox/air bag area are super easy. The PITA is the center vent pod which is linked to the defroster. Took me a few hours do R&R on my 300SD.

Yea, I will probably end up doing that. Hopfully that help drop the vent temp. I think 55/58F is too high but I really dont have anything to compare it to.. I charged up Mike's new 560SEL and it was getting 50F at 75F ambient. So he probably has door problems as well.

Eric what do you get at the vent when its 80F out?

I will try to drive 300SELol today and check for you. This car is on R12, fully charged, rebuilt+resealed system, working aux fans, etc. It certainly feels cooler than mid 50F area.

So I just did some testing on my car today. 95*F out, about 30% RH. Low side at 1200 rpm was 33 PSI. I didn't hook up the high side but it was over 250 since the aux fans were running. Vent temps were about 70*F... kind of meager. The FSM says I should be getting 57*F vent temp, with 21 PSI on the low side and 237 on the high side.

I am running a mix of propane / isobutane for testing. Seems the test is failing.

Is it possible I over charged the system? The suction side line is cool to the touch.

-J

I've noticed the low side pressure seems to move around a lot... like the TX valve is sticking? I got a video of it:

350 SDL AC pressure - YouTube

Any thoughts?

-J

I sure hope it's okay. I just replaced the compressor on my E420 and that fluctuation on the low side is exactly what mine is doing, except it was 100 degrees out and the low bounced from 50 to 55 psi at the same frequency as your video. I am getting cool air out of the vents.

The air from my vents is cool too... not cold. It was about 85* out when I took that video.

I am at a disadvantage because the high pressure connector on my manifold gauge set broke while I was refilling the system and all I have right now is the low side reading. This is the second set of gauges that had the high side break. I guess you get what you pay for with these cheap Chinese products. Using it maybe once a year is difficult to justify buying a good set for $300 but I am almost there. I hope the fluctuation on the low side is normal.

I have one of these manifold sets, just run a google search on them and you'll find em for $66-75 or so.

ATD-3688 - R134a/R12 Air Conditioning Brass Manifold Gauge Set - ATD Tools, Inc.

I haven't had any leaks or breaks with it.

if the txv was sticking, it would NOT fluctuate, or it would pump down into a vacuum...
the txv's job is to maintain a specific superheat value. if the load is low, the superheat will drop, so the txv throttles back the flow of refrigerant to raise the superheat back to it's set value.
raise the blower speed, and the fluctuating will stop.

the value is not to hold a certain vent temp, it's to maintain a specific amount of heat rise over the vapor pressure of the refrigerant in the evaporator. if the vent temps are high, either the heat mix is high, or the refrigerant volume is high.

I have dozens of sets of high quality forged brass manifolds that I do not use because the hoses are dirty for my work.
new hoses are the same price to me as new sets of manifolds...
anybody want any of my sets?

JamesDean: Thanks for the info. I bookmarked the site. Looks like they have some good quality tools there.

Vstech: I actually need the hoses, but if you are interested in selling one of your manifolds with the dirty hoses, I would be interested. Can the hoses be cleaned to use in an auto application? How dirty can they be?

This was the problem. I put in too much gas. Letting a bit out brought all the pressures down, cooling is better. It's super humid here today (77*, 88% humidity). At 1000 rpm i was able to get 48* vent temps with water pouring out of the evaporator drains :cool: (almost a constant stream!).

EDIT: I just checked the chart... it says vent temps should be about 55*F. Woohoo! Working better than factory!

Thanks for your input :D

-J