420SEL AC Pressures - PeachParts Mercedes-Benz Forum

JamesDean · #1 03-21-2012, 04:39 PM

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.

JamesDean · #2 03-21-2012, 06:30 PM

Quote:

Originally Posted by ps2cho

I am no expert, but it looks good.

Any idea where it was leaking out from? Hopefully not the evaporator...

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.

compu_85 · #3 03-21-2012, 07:06 PM

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.

-J

JamesDean · #4 03-21-2012, 07:16 PM

Quote:

Originally Posted by compu_85

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

-J

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

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

compu_85 · #5 03-21-2012, 07:17 PM

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

JamesDean · #6 03-21-2012, 07:20 PM

Quote:

Originally Posted by compu_85

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

So perhaps its still undercharged?

compu_85 · #7 03-21-2012, 07:30 PM

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

-J

just-n-time · #8 03-21-2012, 09:47 PM

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

JamesDean · #9 03-21-2012, 09:48 PM

Quote:

Originally Posted by compu_85

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

-J

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

JamesDean · #10 03-21-2012, 09:49 PM

Quote:

Originally Posted by just-n-time

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

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.

just-n-time · #11 03-22-2012, 10:57 AM

Quote:

Originally Posted by JamesDean

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

compu_85 · #12 03-22-2012, 11:03 AM

Ya, white foam = bubbles.

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

-J

JamesDean · #13 03-22-2012, 05:08 PM

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.

just-n-time · #14 03-22-2012, 09:01 PM

Quote:

Originally Posted by JamesDean

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

Hit Man X · #15 03-23-2012, 12:34 AM

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.

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