300E - Warm air from vents and 3k rpm. - Page 3 - PeachParts Mercedes-Benz Forum

saumil · #31 08-28-2007, 11:29 PM

I still am puzzled. Because no matter which direction the fluid flows, if the monovalve is closed, the scenario with respect to hot water in the heater core is still a normal scenario, and normally we dont get hit by 90-100degF air when RPMs increase. So what is happening at high RPMs to cause the air to turn hot ?

Because your cooling returns when you clip the water inlet, it suggest that air blowing over the heat exchanger is mixing with the cool air from the evaporator. Even when the hot water is present in the heater core, this mixing normally does not occur. So what causes this mixing or mis-diversion of air ? And why at high RPMs only ? The most likely scenario is as Larry and some others have mentioned is a malfunction in the vaccum source or the vaccum elements that control the flaps. If the source of vaccum is the engine intake, then it makes some sense that the situation gets worse at high RPM, because the intake vaccum decreases with increase in RPM. I actually dont know what the source of the vaccum for the pods are but someone else can comment on this.

Bizarre.

gsxr · #32 08-28-2007, 11:47 PM

Quote:

Originally Posted by saumil

I still am puzzled. Because no matter which direction the fluid flows, if the monovalve is closed, the scenario with respect to hot water in the heater core is still a normal scenario, and normally we dont get hit by 90-100degF air when RPMs increase. So what is happening at high RPMs to cause the air to turn hot ?

Makes sense to me. The monovalve is leaking, letting coolant flow when it should not. It's getting pressure from the engine's coolant pump, which is belt-driven, and increases flow at higher RPM. So when RPM's increase, it pushes coolant into the heater core, and voila... hot air at the vent. I'm nearly certain that a new monovalve will cure this. BTW, I would NOT convert to some other type of valve... these rarely fail on a W124 (this is maybe the second I've heard of). I'd just get a new (or used) one.

hispassion · #33 08-29-2007, 01:11 AM

Gsxr, thanks! I am now on the search for a good used monovalve and aux pump since I have to return the pinch clamp pliers to the fleet tech sometime soon. I can only afford so many cups of coffee and honey glazed donuts. I'll not modify the valve/aux pump arrangement and replace it with an OEM part.

Sounds like my engine water pump is working good, especially if it can lift the monovalve's poppet off it's seat with the solenoid engaged. Though if I could look inside, I bet we'd see that it isn't seating properly.

You referenced a manual I'm not familar with. ACC Manual? Diagram 83-600?

I was considering getting the refrigerant switched back to R-12, but when I read that you have to remove the compressor and flush it several times, I may just keep my fingers crossed and pray "black death" doesn't cometh.

This morning on the way in to work, I had 60°F through the vents while the ambient was 85°. This afternoon the Phoenix temp was 109°F and I had 60°F out of the vents with the fan set on auto and 55°F with the fan on low. This, to me is acceptable.

Larry Bible, thanks for your input. I had read that you are usually "spot-on" with your diagnosis of most things on here. I'll check the recirc pod again. If it doesn't hold, I'll change it. Hopefully it's not one they hung with a piece of wire and built the car around.

Again All: thanks for your time and input. It is most appreciated. Hopefully I can be as helpful to someone else on this forum sometime.

Regards,
Michael B.

gsxr · #34 08-29-2007, 10:38 AM

Hi Michael,

ACC is Automatic Climate Control, one of the five printed factory service manuals. It's part of the CD-ROM manual also. Group 83, Job 300. Click here for a link to the PDF, but be warned, it's 15MB.

Reverting back to R-12 requires totally flushing the oil out of the system, part of which includes removing the compressor, draining it, and flushing it with clean mineral oil. Then, the condenser, evaporator, and all the lines need repeated flushing with solvent. And then some more flushing. After all that, you flush it some more, then put the correct amount of mineral oil in, pull vacuum, and re-charge with R-12. Simple, eh?

Your vent temps are high, but let's see what happens with the new monovalve. The recirc flap pods require dash removal... figure 10 hours start to finish for a first-time DIY, but by my third or fourth time I had this down to 4.5 hours. If you pull the dash, replace EVERY vacuum pod, so you never have to do it again. I posted this earlier, but here it is again - more info on the dash removal & pod replacement:
http://***************/forum/showthread.php?t=528

There are two types of monovalves for your car, depending on the build date... the earlier type is more expensive (~$120 wholesale) than the later type (~$80 wholesale). I'd consider getting a new one since the price isn't outrageous. Oh, don't forget to use MB or Zerex G-05 coolant... no green stuff.

James L · #35 08-29-2007, 04:36 PM

83-603 of the service cd "testing the acc with an impulse counter" to read stored fault codes....also 83-604 "checking elec components of the acc".

Also tape up the outside inlet grilles (around monowiper) with wide 3M blue painters tape following with towells and run a/c, this will tell you if you have a blend/flap issue along with 83-603.

On my 1993 fault (same symptoms as yours) code 30 (aux water pump ground fault) keeps comming up.

Do not be so sure it is a refrigerant or vacuum pod problem, it could be an electrical problem. Be sure before you mess with vacuum pods/dash removal or refrigerant.

hispassion · #36 08-29-2007, 11:07 PM

Hey Dave;
Thanks for the manual link. Good stuff. With high speed internet here, I can get 15mb in about a minute.

It is possible the charge is low, but I want to get the monovalve on it first. Once that's done, I'll check the charge. The '86 needs a dash-ectomy, but I successfully put it off long enough and the step-daughter bought it (as is). One of these days someone is going to talk me into doing one for them, I'm sure of it. That is if it doesn't happen to me first.

********AZ is really good at helping ya identify the proper parts. My valve has 1 inlet and 2 outlets. But considering the direction of flow, me now thinks its 2 inlets and one outlet. Doesn't that make it a duo-valve and not a monovalve? (TIC)

Regards for now,
Michael B.

gsxr · #37 08-30-2007, 10:34 AM

Quote:

Originally Posted by hispassion

********AZ is really good at helping ya identify the proper parts. My valve has 1 inlet and 2 outlets. But considering the direction of flow, me now thinks its 2 inlets and one outlet. Doesn't that make it a duo-valve and not a monovalve? (TIC)

LOL - yup, two inlets, one outlet. As long as there's only one valve, I think it's still named appropriately.

Here's some photos of the two types from the Bimby catalog:

Early type (to 04/1990), with heating water feed in top of heater core:

Later type (from 04/1990), with heating water feed in bottom of heater core:

rorypff · #38 08-30-2007, 11:10 AM

The duo valve has two solenoids for a the LH and RH heating circuits - usually found on Euro vehicles.

gsxr · #39 08-30-2007, 02:10 PM

Yeah - it's a real shame we never got the dual-zone ACC offered as an option in the USA. I'd love to have that in my W124's.

Dee8go · #40 08-30-2007, 02:13 PM

Quote:

Originally Posted by rorypff

The duo valve has two solenoids for a the LH and RH heating circuits - usually found on Euro vehicles.

I always wondered how that worked, but not enough to find out. Thanks for the explanation.

hispassion · #41 03-26-2008, 11:57 PM

Well, I procrastinated all winter and just replaced the Monovalve. Problem solved! 40°F out of the center vents at highway speed.

Actually, since we do have winter here in Arizona, I wasn't that concerned as I was getting plenty of heat. So, when the belt tensioner horked, I replaced a bunch of stuff while I was under the hood.

There are threads after threads on this forum regarding the belt tensioner on the M103, but let me say one thing about it here in this thread. It is not a job for the weak and hasty people. And DO NOT tighten the large (19mm socket) pinch bolt until you've adjusted the belt with the adjusting nut.

Anyway, much appreciation to all who help me solve my creature comfort problem.

Regards,
Michael.

booker_noe · #42 11-15-2008, 11:00 AM

Hi Guys great thread -
can anyone give me a heads hup why I cant dial down the temp (I got dual zone temp - two dials), get constant hot air from vents.

where to start checking ??

A/C compressor fires up nicely, pipes get cold, but mixes with hot air in vents

Cheers.

gsxr · #43 11-18-2008, 11:19 PM

Quote:

Originally Posted by booker_noe

Hi Guys great thread -
can anyone give me a heads hup why I cant dial down the temp (I got dual zone temp - two dials), get constant hot air from vents.

where to start checking ??

A/C compressor fires up nicely, pipes get cold, but mixes with hot air in vents

Sounds like either an electrical issue (duo valve not receiving electrical signal), or a failed duo valve allowing hot coolant into the heater core when it's not supposed to. You'll have to do some deeper investigation.