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Is there a simple way to make my ACC always blow hot?

Started by Ilike300sd, 27 September 2011, 08:46 AM

Ilike300sd

My ACC seems to work in terms of the fan blowing and sending air to the correct ducts but there is no change in temp when I dial hot or cold.  Since we are going into winter, I just want to manually set it up to always blow hot.  Is there some part that I can bypass that will always allow coolant to the heater core?  Or some other simple bypass/change I can do to make it always blow hot?

Thanks for any help.  I did look at some of the old threads such as http://forum.w116.org/mechanicals/heater-servo-amp-replacement/msg72286/#msg72286 and I know there are some fairly high cost repair options such as http://unwiredtools.com/accii.asp.  All I need is a simple "bypass the control valve" type option, if such an option exists.  I don't need A/C at all where I live.  In summer I can take the "bypass" back out.

Casey

The ACC Servo is connected to coolant lines that run underneath.  I've seen it bypassed and connected to a manual switch in the car where you just adjust the flow of what goes through these tubes manually.

The 300SD at the junkyard near me has one of these installed:
http://mercedessource.com/node/606

I pretty much destroyed the plunger switch trying to get the underside of the dash off, though.

Personally, if I were going to go the cheap route like this, I wouldn't drill a new hole in the dash to put a convenient switch in - I'd be content with opening the hood to make an adjustment.  That way you could always do a proper repair later on when you have more money (or the next owner).

Ilike300sd

Seems like you could just bypass the servo with one piece of tubing (+ 2 couplers) for the "flow" side and another piece (+2 couplers) for the "return" side and just bypass the servo completely? 

I haven't looked yet to see accesable the servo is.  Also, I wonder if this would mess up anything else.  It shouldn't because the vacuum part of the servo is seperate from the valve part.  It shouldn't know that there is no coolant flowing through there.?



1980sdga

Are you blowing out hot now?  I would install an on/off valve between the engine and heater core.  The unwired tools site has instructions and vacuum diagrams that I found useful troubleshooting mine. The pics aren't from 116's but it could give you some ideas.

It depends on how much time/$$ you want to invest.

You may enjoy the car so much that you want to go further than a stopgap measure.

Ilike300sd

#4
@raptelan, where is the servo located? 

If under the hood, this would be a 15 minute, $10 "bypass fix".  You could put a manual valve inline and just manual turn it on or off depending on season.  It's ghetto of course but would suit my needs just fine in terms of how much I drive the car.  If usage changed, then I could do a more convenient/comfort/oem/expensive fix. 

Edit: 1980SDGA, Just saw your post. We're thinking along the same lines.  As a weekend only car the cheap bypass is fine. As a daily driver the more expensive fix would be warranted. It always blows cold now so the existing servo vavle is "off" by default at the present time.

1980sdga

You are correct about the water/ vacuum-electric separation in the servo. Water should stay in the lower 2 pieces if all is well ;D  This modification was free:





Here's some more pics of the servo:





The last pic shows the hoses without the servo installed. The hoses closest to the firewall are where the valve portion was. The 2 hoses in the far left corner were just a straight through passage with a vacuum temp switch. The temp switch cuts off vacuum from the system until the engine warms up but it's easily bypassed.

You will probably want to just keep the aux. water pump in place. It's the little pump in the last picture. I'd oil it from the top and check the fuse. It's a simple on/off deal controlled by a temp sensor behind the glove box liner. It comes on any time the temp gets below 79 F (I think). Pretty easy to test with a bag of ice on the sensor. Even if it doesn't work I would keep it in place to save on plumbing.

Casey

Quote from: Ilike300sd on 27 September 2011, 09:19 AM
@raptelan, where is the servo located? 

If under the hood, this would be a 15 minute, $10 "bypass fix".  You could put a manual valve inline and just manual turn it on or off depending on season.  It's ghetto of course but would suit my needs just fine in terms of how much I drive the car.  If usage changed, then I could do a more convenient/comfort/oem/expensive fix. 

Yep.

Ilike300sd

Sweet!  I'll pick up some hoses and a valve at the hardware store and be off and running.  Then I can upgrade later but for right now I just need some heat.  Thanks very much guys.

Papalangi

Mine has had a ball valve bypassing the servo for 5 years now.  Closed during the summer, part open spring and fall, wide open during winter.  I really don't touch it more than once every 3 or 4 weeks.

Michael
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8

Ilike300sd

Sweet, that is exactly what I was thinking as far as the valve and 3 times per year or whatever! 

I read some of the old maintenance records and it looks like the mechanic diagnosed the auxiallary water pump as seized early in 2011.  So they probably didn't want to pay the money to replace the pump.  I think I will try bypassing the pump first, since now I know that is a known problem.  Perhaps if I bypass the pump then everything else will work as normal.  Fingers crossed.

Gonna take the 300SD into the mechanic tomorrow to have him adjust the valves.  I didn't want to order the special wrenches and all because it's about the same money to have the mechanic do it as buying the wrenches.  Plus these guys are MB diesel specialists and I can have him give it the once-over just for kicks.  The car has a huge fuel tank in the trunk and I'd like to know if that is functional as is or not.  No record or indication that the previous owner was trying to do biodiesel.  It looks like just an extra tank for more range.  that would be cool if it's functional.  Could put like 40 gallons in it at a time I would guess.

Casey

Quote from: Ilike300sd on 29 September 2011, 12:08 PM
Gonna take the 300SD into the mechanic tomorrow to have him adjust the valves.  I didn't want to order the special wrenches and all because it's about the same money to have the mechanic do it as buying the wrenches.  Plus these guys are MB diesel specialists and I can have him give it the once-over just for kicks.  The car has a huge fuel tank in the trunk and I'd like to know if that is functional as is or not.  No record or indication that the previous owner was trying to do biodiesel.  It looks like just an extra tank for more range.  that would be cool if it's functional.  Could put like 40 gallons in it at a time I would guess.

You don't need special wrenches - you just need regular wrenches that aren't too thick, and a feeler gauge.  I got the special wrenches as they came with the 300CD I bought, but I used regular wrenches too because in some cases, they were an easier fit.  Considering that you need do do this every 12k miles, I don't think the wrenches and personal know-how are a bad idea, but that's your call. :)

I found one of those extra fuel tanks in a junk yard and bought it - it's sitting in my garage right now. :)

Casey

In this video I show the manual climate control override in the junk yard car, which I believe is the one MercedesSource offers:
http://www.youtube.com/watch?v=2wg2QlSwjJI

(it's after all the tow bar stuff)

Ilike300sd

#12
I bypassed the little motor that keeps coolant going to the heater core.

1980sdga

I've been working on the problem and recently found this:





It's from a 1990 Chevy Astro 2.5 litre. I got it at Autozone for about $30.  It's a bypass valve like the servo and has a little flapper valve in it. It's normally open so vacuum going to it would close it.

If the auxilliary coolant pump works I'd keep it. It just comes on when the temp gets under 79 F and the ACC is on.  I'm working on figuring out how to switch the valve.

Ilike300sd

#14
Very cool!  You are onto something there!  I think it would be easy to hook it up in on/off (i.e. vacuum or no vacuum, hot or cold) but to get variable vacuum (i.e med hot, med cold, etc) that might be harder.  Really all you would need is a simple air valve.  Ideally one that looked good inside the cabin.

update to the "bypass servo" attempt: success! We have heat!  going to watch 1980sdga's progress on the valve and vacuum actuated bypass.  HOpefully there will be a DIY when a good solution is found. 

For someone referencing this thread in the future:

if your little motor freezes up (thus stopping flow to the heater core) you can od the following: 1) unplug it, 2) leave it where it is, 3) remove the hose between it and the servo (if you remove the 2 10mm nuts that hold the servo onto the bracket it will be easier), 4) remove the hose off the bottom of the little motor, 4) install the hose that formerly went to the bottom of the little motor into the servo.

To bypass the servo, unplug all four hoses going into the servo and insert a barbed metal pipe between the hoses. keep the hoses on the same side (rear to rear, front to front).  it takes like 10 min.  It would be better to install a valve, either manual or cable, or vaccum like 1980sdga above instead of one of the metal pipes.  I just used 2 pipes as a quick and dirty way to have it "always hot" as we are going into winter.