87 300SDL AC blowing out defrost after replacing vacuum rubber - PeachParts Mercedes-Benz Forum

RamahX · #1 05-19-2012, 08:36 PM

87 300 SDL, AC and engine running great, until today - I started replacing rubber tubing on the vacuum hoses (as per the ************** guy) because alot of it was starting if not already dry-rotting.

Now AC is blowing COLD but out of defroster only, all settings.

I was doing one at a time so I wouldn't get anything mixed up, but maybe I knocked something loose or have a vac leak from using the wrong hose?

I found the line from the 5-way to Y-31 Vacuum Transducer/Recirculating Valve was intentionally plugged up with a bolt. When I pulled it off air leaked/sucked in... I replaced that piece and hooked it back up as per, and also found line from 137b Recirculating Air Valve on the Exhaust Gas Turbocharger completely broken off, so I repaired/replaced that also.

I have also discovered a large black hard hose, should be 'a' Ventilation to Passenger Compartment unhooked-and/or pulled out from the fire wall behind the brake booster. It just stops there. That's the so called henstooth? and runs to the gas looking filter at Y-31...

I've been searching the forums but overwhelmed...

Was the blocked hose from Y-31 intentional to keep the 5-way charged? Meaning could Y-31 be bad and allowing vac leaks needed for the ACC to control the flap from defrost to the center vents?

sixto · #2 05-19-2012, 08:52 PM

Here's an image to help anyone who can help -

EGR is typically disabled by interrupting the vacuum signal to prevent soot build-up in the intake manifold. ARV is typically disabled because there is no need to preheat the trap oxidizer when it's removed per the recall, thought there might be another function of ARV. To facilitate diagnosis, disconnect and plug the 5-way fitting branches for EGR and ARV. They're the lines that go over the radiator towards the passenger side headlight.

The emissions devices are probably not involved in your issue if you aren't complaining of stiff shifts since the transmission modulator is fed off the same vacuum pump as the ACC.

The thick black line is a vent for the various vacuum users. It goes through the firewall and ends near the pedals.

Sixto
87 300D^2

RamahX · #3 05-19-2012, 09:28 PM

Thanks for the quick reply Sixto!

Unhooked and blocked both lines to the recirculating valves, and pulled the hose off the EGR. Didnt fix the ACC. Test drove and no transmission problems. Gotta be something I did.

To recap my day:
1. changed the oil and filter (to Mobile 1)
2. changed the serpentine belt
3. replaced vacuum hose rubber. Lots of it.
It's after I did all that that the ACC is not shifting the vents from defrost to the main. It's still blowing strong and COLD though. It's gotta be something I did...

Car is smoking a little now also.

sixto · #4 05-19-2012, 09:36 PM

There's a yellow(?) check valve on the false firewall ahead of the brake booster. One line from the 5-way fittings and splits on the aft end to a line that goes in the cabin for the ACC and a line into the driver side fender for the vacuum reservoir. Check that the connections are solid into and out of this check valve.

The vacuum pump has no bearing on engine smoke.

Sixto
87 300D^2

brandlj · #5 05-19-2012, 10:58 PM

The default setting for ACC is defrost only. If you have a vacuum hose in the engine compartment loose, you will have a hard shifting transmission AND all air out of your defrost. If the transmission is shifting just fine, then you must look at the vacuum hose that goes into the vehicle that controls the vacuum for the ACC.

brandlj · #6 05-19-2012, 11:01 PM

Quote:

Originally Posted by brandlj

The default setting for ACC is defrost only. If you have a vacuum hose in the engine compartment loose, you will have a hard shifting transmission AND all air out of your defrost. If the transmission is shifting just fine, then you must look at the vacuum hose that goes into the vehicle that controls the vacuum for the ACC.

Specifically ( c ) the green vacuum line. trace it all the way from the 5 way fitting

RamahX · #7 05-20-2012, 01:06 AM

Ok, 2 things...
(first off, thanks again guys for helping)
1. I tried to match up the hose at the store - ended up with 5/32 and just converted that and it's 3.96mm. Finding out hose is supposed to be 3.5mm

2. With that in mind could I have very small leaks EVERYWHERE and the sum total equals loss of vacuum overall, enough to not pull the ACC door over from defrost to regular?

Embarrassing as this is I'm only out $3.91 worth of hose. Will try and find some 3.5mm tomorrow and try again...

Question, where can I find quality hose, "y's", and elbows without going to the "A" stores? Or do I have to order it online?

RamahX · #8 05-20-2012, 01:38 AM

Also my vac lines don't match the diagram. For instance the Y that's supposed to be on the ALDA is actually on the manifold. Should I make it right as per or leave it all alone?

sixto · #9 05-20-2012, 01:54 AM

Hose size isn't the problem but change it if you feel you should. Who knows, you might find where the ACC supply hose is disconnected or misrouted in the process.

The Y location doesn't matter as long as the overboost solenoid is between the manifold and ALDA. The overboost circuit will limit boost before overboost damages the transmission vacuum amplifier. Besides, and I'm kidding, you have a history of causing things to not work when your hands get involved

Seriously though, it makes you wonder what the person who left things this way was thinking.

Sixto
87 300D^2

RamahX · #10 05-20-2012, 08:38 AM

The yellow check valve and green line are eluding me... From the ACC Vac diagram diagram do you mean:
check valve #36 with a line running to #37 vac reservoir? The only line I can find coming off the Intake is the one going to the overboost switch for the ALDA...

I'm missing an obvious item somewhere... I take it I can disconnect the EGR/ARV lines at the 5way and plug those 5way ports, right?

Bio300TDTdriver · #11 05-20-2012, 09:35 AM

I know the OP has a 126, but for anyone with a 124 using that schematic it does not show the vacuum reservoir located behind the passenger wheel well or the vacuum line going to the reservoir.

The schematic for Model Year 1988 shows the reservoir.

sixto · #12 05-20-2012, 01:24 PM

Quote:

Originally Posted by RamahX

The yellow check valve and green line are eluding me... From the ACC Vac diagram diagram do you mean:
check valve #36 with a line running to #37 vac reservoir? The only line I can find coming off the Intake is the one going to the overboost switch for the ALDA...

I'm missing an obvious item somewhere... I take it I can disconnect the EGR/ARV lines at the 5way and plug those 5way ports, right?

That's a gasser diagram with the manifold as the vacuum source. Your SDL is different only in that the vacuum source is the pump. The check valve and reservoir should be the same.

Sixto
87 300D^2

RamahX · #13 05-20-2012, 01:29 PM

Going out to look for a Mityvac or the equivalent. I've read so much on SDL ACC vacuum I'm gonna pop!

Next is to convert 5way to "F", check reamining lines for clogs and then use Mityvac to test lines. Will post results. HOPING it's not a bad pod inside.

RamahX · #14 05-20-2012, 07:30 PM

Okay shipmates, got myself a Mityvac! Will tackle this tomorrow morning. Piña Colada's with COMHSELANT tonight takes precedence.

Any pointers? Also, can I damage the vacuum pump or peripherals by drawing a vacuum with this?

RamahX · #15 05-20-2012, 11:21 PM

Just verified the line going in the cabin is good, Mityvac pulled the defrost vents closed and AC blew strong and cold out of the dash vents. Vac held good and long.

Rest of the system is another story. While tx and shutoff valves/lines are good, all my replacement joints leak. I guess 5/32 hose is not good enough.

I'll look for a source of 3.5mm hose and fittings or just haul off and order it.