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Wanted to archive this on the forum in case anyone has an unexpected issue with the heat not working.
Here’s the part I just replaced
It’s located behind the removable firewall just under the windshield wipers.
Was a fairly straightforward job just took me a while trying not to break things.
Ideally if you use vice grips for those clamps things will go smoother but I found using a long needle-nose gave me better reach.
Be careful — if you look closely at the photo above there appears to be one clearly intact hose connection on the upper right side of the piece.
There are actually supposed to be 4 prominent connections—see the new piece here:
All the connector were broken in the coolant tubing. You may run into this issue so I’d recommend moving the clamps a little farther back than needed then using a vice grip or something to close off the coolant line as much as possible to ensure no pieces get into the system.
You can then easily use a small flathead or something to remove the eroded plastic pieces. I then just used gravity to clear the remaining debris by letting excess coolant spill out each line tilting them downward and feeling for any pieces at the same time.
Of course, make sure the car has sat for awhile (preferably overnight)
There is a electronic connection in the back. The best way I found to disconnect without breaking or harming the wire harness is to use a small pair of pliers to hold the sides—then with your other hand press the tab and push everything downward.
This way, the wire harness stays held in place safely and you can control the downward pressure vs pulling on the harness and risking damaging the wire or more commonly breaking the little tab/clip that locks it in place.
Finally, have extra coolant on hand before you start because—as I learned the hard way—you will lose a significant amount of coolant.
mine and the guy with the CL have both found the heat is vanishing winter by winter - each year we have to wind up the heat by 1 C more - keep meaning to ft one of these - the really strange thing is a big well reputed indy that's been going 25 years and even owns an S600 221 claims he's never fitted one on a 221 - yet this is the std part that fails all day long and is the bit that cuts the heating
mine and the guy with the CL have both found the heat is vanishing winter by winter - each year we have to wind up the heat by 1 C more - keep meaning to ft one of these - the really strange thing is a big well reputed indy that's been going 25 years and even owns an S600 221 claims he's never fitted one on a 221 - yet this is the std part that fails all day long and is the bit that cuts the heating
Interesting… I did notice that last winter I needed to use the max “HI” temp more often as it was taking forever to get warm and even then it wasn’t that hot.
Today, after installing the new piece there is a very clear difference and the “HI” max temp is blazing 🥵 so it makes a difference for sure.
I replaced that preventatively on mine (it wasn't broken) but before, and after, my complaint is that the HVAC system waits for the engine to be nearly warmed up before blasting you with heat. It seems to be by design?
leaving the controls like they are supposed to be, just a thermostat - (when the heating comes in at home, if 10 outside if offers full heat - it doesn't respond more if turn the stat on at 22 or 30C its either on or off - what changes is the closer the ambient temp is to the setpoint (the earlier it cuts the pump) in the car which is a bit more sophisticated, it brings less heat it brings to the party - the idea on BOTH its aiming to never overshoot its setpoint.
So back in the car - when set at 21C / 70F if its the same 10C outside, it should produce a glimmer of heat (inside the car) within 100 yards of starting, and proper heat inside half a mile - thermostats are renowned on Merc's to be the least durable fitted on any brand of car - try a new one
useless site - why do I only get 30 seconds to check and tidy a post (most provide an hour or the better ones unlimited without the detritus below).
I replaced that preventatively on mine (it wasn't broken) but before, and after, my complaint is that the HVAC system waits for the engine to be nearly warmed up before blasting you with heat. It seems to be by design?
I think in general it is by design. I daily drove what is arguably one of the best sedans of all-time (Lexus LS430) and as flawless as that thing was in every way—even it had a “warming up” period where the the heat wasn’t as hot or in the summer the cool air wasn’t as cold—both seemed to coincide with the engine reaching normal operating temp.
So yes, definitely think there’s a +/- a minute or so on a cold start after the vehicle has sat for many hours or overnight where the air coming through the vent upon startup does necessarily match the specific temp setting to the exact degree.
That being said, after driving for a few minutes and reaching normal op temps but still feeling “cool” vs ice cold air (if you set to MAX cool temperature to test) or “warm” air (if you set to HI heat temperature to test) then it may be time to get proactive and do some preventative maintenance.
Wanted to archive this on the forum in case anyone has an unexpected issue with the heat not working.
Here’s the part I just replaced
It’s located behind the removable firewall just under the windshield wipers.
Was a fairly straightforward job just took me a while trying not to break things.
Ideally if you use vice grips for those clamps things will go smoother but I found using a long needle-nose gave me better reach.
Be careful — if you look closely at the photo above there appears to be one clearly intact hose connection on the upper right side of the piece.
There are actually supposed to be 4 prominent connections—see the new piece here:
All the connector were broken in the coolant tubing. You may run into this issue so I’d recommend moving the clamps a little farther back than needed then using a vice grip or something to close off the coolant line as much as possible to ensure no pieces get into the system.
You can then easily use a small flathead or something to remove the eroded plastic pieces. I then just used gravity to clear the remaining debris by letting excess coolant spill out each line tilting them downward and feeling for any pieces at the same time.
Of course, make sure the car has sat for awhile (preferably overnight)
There is a electronic connection in the back. The best way I found to disconnect without breaking or harming the wire harness is to use a small pair of pliers to hold the sides—then with your other hand press the tab and push everything downward.
This way, the wire harness stays held in place safely and you can control the downward pressure vs pulling on the harness and risking damaging the wire or more commonly breaking the little tab/clip that locks it in place.
Finally, have extra coolant on hand before you start because—as I learned the hard way—you will lose a significant amount of coolant.
Hope this helps someone!
Great post. Would you have the part number handy for this wacky looking valve?
I'm thinking about replacing this. I can't find the WIS instructions for the job. You sometimes how one job is hidden inside the instructions of another job...well, I can't find this anywhere. Would someone mind posting a PDF of the remove/replace instructions for this valve? Thanks in advance.
Another question about this job....do parts 180 and 190 in the diagram go directly to the heater core? I've never done this before, so am trying to learn the best I can before jumping in. I'm thinking doing a flush of the heater core might be worth it, as long as the coolant is drained and the heater control valve is out. Please let me know if this is wrong and/or a bad idea.
ANY modern car running the OEM fit coolant mix should, if maintained appropriately never need a flush - you'll likely add more air and have more fun with zero benefit
cars's heaters used to play up when the cast iron block would self destruct adding 3 ounces of rust to block up small pathways, we didn't understand how to make a good antifreeze, it leaked so much people would top it up with rubbish, and the heater tap was shut of and we'd have no coolant flow for 6 months....
the world moved on (I thought) for many years now the heater matrix is part of the cooling systems capacity and its just the hot air we waste - throwing it away or warming up the passenger compartment....
the coolant in a Merc of this vintage is 12 years fit and forget
Another question about this job....do parts 180 and 190 in the diagram go directly to the heater core? I've never done this before, so am trying to learn the best I can before jumping in. I'm thinking doing a flush of the heater core might be worth it, as long as the coolant is drained and the heater control valve is out. Please let me know if this is wrong and/or a bad idea.
So 180 & 190 do.
You will lose a significant amount of coolant doing the job so if you wanted to plan to flush the entire system during the job it wouldn’t be a bad idea at all.
I didn’t plan to flush but needed to replace just under 4 qts.
You will lose a significant amount of coolant doing the job so if you wanted to plan to flush the entire system during the job it wouldn’t be a bad idea at all.
I didn’t plan to flush but needed to replace just under 4 qts.
Thanks for your reply. I flushed the coolant and replaced all the hoses, tank, and temperature sensor a few months ago, so my plan was to drain it at the radiator and reuse it. I wish I would have done the heater valve at the same time, but hindsight is 20/20. Sounds like Botus thinks flushing some water through the the core is a waste (and maybe worse), so I'll skip that.
I do agree that flushing should never be required. But when conditions deteriorate, "typical recommendations" may no longer apply. On other vehicles I have had success forward and reverse flushing the heater core with just a garden hose sprayer. I usually try to blow out with air and also rinse with distilled water just for good measure. I don't know anything about whether these heater cores are particularly fragile but I've never caused damage from a flush as described. Again, only on vehicles that seem to have a problem with heat (I wouldn't do it preventatively).
what water are u using to refill these - modern cars with long service life coolant (as I say Merc say don't touch for 12 years in the handbook) don't use rubbish out of a tap you drink from....
Me personally? Either 50% concentrate + 50% distilled water, or, pre-mix. It seems like I am doing way more pre-mix for the past several years for whatever reason.
As for the schedule, what I am currently seeing is coolant is a service 13 (for 2007 W221 EXCLUDING AMG and S600 models). 143k miles and 15 year interval. Yeah, I don't agree with that. I'd put it more on a 5 year schedule (almost regardless of mileage).
09-21-2023, 12:03 PM
