I am still attempting to resolve the no heat issue in my vehicle. Over the past couple of weeks, I have implemented multiple methods to flush out my cooling system, specifically targeting what I believe to be a clogged heater core, utilizing Thermocure, CLR, and vinegar to restore heat. Notably, vinegar yielded impressive results, albeit short-lived. Within the past two years, I have replaced the thermostat, water pump, circulation pump, auxiliary pump, and changeover valve, resulting in minimal improvement. Following the cooling system flush with vinegar, I achieved temperatures of 113 degrees at the vents, whereas previous temperatures with Thermocure and CLR were 85 degrees. The cooling system flush did dislodge sediment, which was likely due to the previous owner's maintenance habits. After reviewing a YouTube video, I became aware of an electronic heater valve located behind the engine block, part number 272-200-00-31, distinct from the firewall and situated near the cylinder head. I am currently experiencing a DTC 90A2, indicating low coolant capacity. Given the cleanliness of my heater core post-flush, I strongly suspect that this part has failed. Can anyone provide insight into the difficulty of replacing part number 272-200-00-31?

 

Botus, to correct you, no changes were made to the heating button or the HVAC system. Also, I disagree with your assertion that the heater core was not clogged to some extent, considering the considerable amount of garbage present in the cooling system, which can be attributed to the previous owner's failure to properly maintain the vehicle. The pictures provided serve as evidence.






Those particular are dirt, rust, and other stuff that came out of the cooling system. This after 2-3 flushes of vinegar.

 

blend doors and actuators all verified and in working order as per star computer.

 

So now we are at the replacement/testing of the valve at the back of the engine. That's all that's left, correct?

 

This is after thermocure and Prestone flush

This is after the vinegar flush

 

I have ordered the necessary valve and will maintain continuous flushing of the system. While we have time before the onset of cold weather, I am hopeful that the heating issue will be resolved.

 

Looks like a pain to replace.

 

That's not the thing those cut wires plug into is it?

 

So far the only mention of that heater valve im seeing in the maintenance manual is for removing the cyl head, mentions removing the hose from the heater valve as one of the steps. Im sure theres instructions on it somewhere.


Two bolts hold it to the head. Found a better photo of it on the head, in the photo the hose is cut off.

 

Oh, I see the post about the cut wires above. Doesnt look like it unless its near the throttle valve harness.

Not sure what that 90A2 code is cant find much info on it. I did search for possible codes related to the heater valve.

Photo of M272, should be the same for M273.

 

I would like to provide a few updates: the heat valve is expected to arrive tomorrow. I have applied Prestone cooling system cleaner, using two bottles instead of the suggested single bottle, and then drove the vehicle for six hours. I have decided to leave the cleaner in the system for a longer duration. Yesterday, I observed that the vent temperatures were barely reaching 80 degrees, which is lower than the usual 90 degrees. However, it is unclear whether this reading is accurate or an optical illusion. I have obtained codes related to the ACC unit, but I remain skeptical and would appreciate guidance on where to focus my examination of the LINBUS. The codes are provided in the attached image. Once I complete the Prestone flush, I plan to flush the system with water and then add Thermocure. I suspect that the heater core may be clogged again, but I am not willing to give up. I am considering using vinegar prior to Thermocure, as it may help to accumulate rust and sludge in the system, potentially clearing the clog in one area but causing it to occur elsewhere in the heater core or system. Using Thermocure after vinegar may be beneficial in cleaning the rust and sludge.

 

are the recent posts from TimC300 suggesting there's a heater valve for the heater valve - somewhat overkill ?

is that part of the REST BS

 

Botus,

Interestingly, there is indeed a heater valve. Additionally, Mercedes exhibits inconsistency, often over-engineering minor aspects while neglecting critical components.

 

I was wondering how the coolant flows to the heater core so looked at 221.071 diagrams unfortunately theres a few for the lines.

As far as I can figure the coolant from the drivers side cyl head flows thru the heater valve (150), thru hose (60), to pump (10), thru hose connection (90- this hose shown in the photo in Post# 1), thru ac water valve (170), thru hoses (180/190) , then line (15) to the heater core (60).

Is the entire cooling system being cleaned? I was thinking those two hose (180/190) can be accessed and use something like a fluid transfer pump to flush the heater core by itself.





I think those two hoses below the hose with the clamp on it go to the heater core. The ac water valve should be under it. I could be wrong.

 

Found a used ac water valve assembly with the pump attached to see what it looks like in the car:

 

Tim- bro is ON it!

 

Yesterday was a productive day, and I feel like I'm making progress in the right direction. For those who have been following this thread, you're aware that I've conducted numerous flushes using various products, including CLR followed by white distilled vinegar. Initially, I believed that I had successfully removed most of the CLR from the cooling system, but as I later discovered through a YouTube video, some residue remained in the engine block. I'm convinced that the CLR/vinegar combination was the catalyst for the improving heat performance. Although the system became clogged again, I subsequently used Prestone cooling system cleaner and distilled water, which yielded impressive results yesterday, with vent temperatures exceeding 100 degrees. The heat was functioning optimally, and it appears that the issue has been resolved. I plan to recheck the heat today after allowing the car to cool down. Additionally, I need to replace the upper radiator hose and air mass flow sensor, as well as the crankshaft position sensor, as I've received codes for both, and they are relatively inexpensive to replace. I've already acquired the necessary parts from RockAuto, which are OEM brands. I'm still considering performing the thermocure as a final flush before conducting a vacuum fill of the cooling system. I will also replace that valve Tim had pointed out as part of the maintenance as it has 196k miles on it.

 

Prestone cooking system flush and distilled water flush

 

I am hopeful that I am finally approaching a breakthrough. In recent weeks, I have employed a range of treatments, including Thermocure, Prestone, and white distilled vinegar, yielding satisfactory results. These efforts successfully eliminated a substantial quantity of waste from the cooling system. As previously stated, I have achieved the most significant progress using distilled water and vinegar, attaining temperatures above 100 degrees from the vents, which was encouraging. Regrettably, after shutting off the engine and permitting it to cool, I experienced a decline in performance. Upon restarting the engine the following morning and allowing it to warm up, I retested the temperatures and obtained readings ranging from 77-90 degrees with the heat on full blast. I concluded that the rust, sludge, and debris within the system were finding alternative locations to accumulate and obstruct the heater core.

I undertook a comprehensive search of the internet, YouTube, and consulted with mechanic friends to uncover novel approaches to addressing my issue. A YouTube video caught my attention, showcasing a flush utilizing CLR, white distilled vinegar, and distilled water. While acknowledging the potential risks of CLR and vinegar, I considered them justifiable at this stage. My son assisted me in replicating the video's instructions, which entailed mixing 1 gallon of distilled white vinegar, 64 ounces of CLR, and topping off the cooling system with distilled water. The theoretical basis is simple: vinegar breaks down scaling and rust accumulation on the heater core, whereas CLR dissolves the broken-down substances, preventing new blockages. The initial outcome was somewhat underwhelming, as the vent temperatures only attained the mid-90s after 30-45 minutes of idling with the heat on high, falling short of my previous temperatures above 100 degrees.

The second day of the solution in the car showed promising results as the vent temperatures increased rapidly upon warming up, meeting my expectations. The temperatures from the vents reached a high of 111 degrees, which, while commendable, I think can be improved upon. The time it took to reach this temperature was approximately 20-25 minutes while the car was idling; however, I believe driving the car would have reduced this time. Therefore, I will continue to use the solution for an additional two days, allowing it to work to its full capacity. Although aware of the potential risks, I remain cautiously optimistic.

To conclude, I have discovered that utilizing distilled water in conjunction with flush products produces superior outcomes for me, contrary to the typical advice to use regular water. Distilled water costs roughly $1.25 per gallon, a price I consider reasonable. My vehicle requires approximately 1.5 gallons of distilled water per flush, but I find the cost to be worthwhile. If I had brought my car to a shop for this service, most mechanics would have probably advised replacing the heater core instead of dedicating the necessary time to perform a thorough flush.

 

Update : I added thermocure and acccording to the thermocure instructions, it is recommended to keep the product in the cooling system and drive for 3-4 hours. However, I plan to keep it in the car for several days, driving it periodically during this time. Today, being the second day of the thermocure treatment, I was astonished by the results. The heater core/evaporator temperature reached 120.3 degrees, while the vent temperatures were 120 and 121 degrees. The heat in the car felt like a sauna. I repeated the test hours later and obtained similar results. I am extremely satisfied with the outcome and the car is now prepared for the winter months. I would like to express my gratitude to the forum members who have assisted me throughout this process. I will provide a final update once I have completed flushing the thermocure out of the system, which will likely take another week, and then installed the correct coolant.

 

glad you made progress with the cold coming

 

Glad you are making progress. I might add that since you have been constantly opening the coolant circuit, it's highly likely that during some of these tests that you have had air in the system. You mentioned a low coolant light once and this may have been the cause. Make sure you vacuum bleed OR run the car a few times up to temp with time for a cool down so you can add more coolant. Also, im sure you know but when doing a heater core flush, run the "garden hose" in the opposite direction of coolant flow to push debris out the way it came instead of trying to push the debris through the "clog".

 

Using acidic products such as CLR dissolves the ick that occludes coolant flow to the heater core. The ick that plugged up a heater core happens due to very old coolant that made for incorrect PH in the cooling system. This is assuming the car has been filled with modern coolant all its life. If filled with coolant with silicates in it (as was in the case from seemingly the dawn of time until the late eighties) you can expect a plugged heater core as well as a plugged radiator core. Decades ago this was a regular occurrence. ‘The bad old days’ for clients. Great for skilled mechanics.

OP be sure to test the PH of the cooling system once you have things sorted as too high or low PH makes for electrolysis in aluminum parts that dissolve away to make leaks or worse.

 

What happened? How did it turn out?