Heater problem

[Kyiv]

I almost don't get any heat from my heater, other than in defroster mode

1. A) It's kinda slow to come on and then, usually after a few or sometimes several minutes the air turns lukewarm.
B) air output is kind of half-strength of what it should be

2. AC seems to be working just fine and air output seems appropriate for selected speed

3. Windshield defroster pumps good heat at high speed - as it should - and that's what I'm using for warmth. In this mode I get good output from corner and bottom of windshield vents

4. Monovalve is only a few months old, MB part.


Who's got an idea? Thanks

 

[gerryvz]

Check the following:

- thermostat operation — is engine coming to temp?

- aux coolant pump operation

- it is possible that new monovalve could be defective, but only as a last resort.

Nearly 100% likelihood that it is auxiliary coolant pump.

Ac blows cold from center vents and hot from side vents | Heating and Cooling (Interior HVAC systems)

I have this problem only on very hot days, over 95, while driving in traffic or after parked for awhile. The AC will be working fine then suddenly extremely hot air comes out of the side vents while the center vents continue to blow cold air. I found that by switching the control to the next AC...

www.500eboard.co

 

[gsxr]

Sounds like you may have a couple different issues. The thread linked above may help.

Quick test: Unplug the electrical connector on your new monovalve. This SHOULD force max heat all the time. If not, you may have the AC running simultaneously. Either way, the pushbutton unit is the "brains" of the HVAC system and there could be an issue there. Any chance you have a spare PBU to swap out? Only takes 5 mins.

You also noted weak airflow - this is a separate problem. First verify air is only coming out vents that it should (see owner's manual or FSM for airflow diagrams). If your fan is on high speed and just not blowing much air (i.e., not full max speed) the blower regulator might be failing.

 

[Kyiv]

Sirs, thank you. Did not even know there is such a thing as aux water pump! Quick search shows Bosch unit is under $80

thermostat operation — is engine coming to temp?

Yes, engine gets to operation temperature in appropriate time and stays there

Quick test: Unplug the electrical connector on your new monovalve. This SHOULD force max heat all the time.

Will try

You also noted weak airflow - this is a separate problem.

That's only in heating mode. In A/C or windshield defrost airflow is appropriate to selected speed

 

[gsxr]

In normal heating mode (button #4 of 5 pressed), and temp set to hot (red zone), where does air come out? Should be strong airflow from dash end vents and footwell vents, weak airflow at the windshield, and zero air out the center dash vents.

 

[nocfn]

vac pod issue? This is deep into the weeds but the advice above is great, TEST is a 4 letter word, but necessary. The vacuum distributor inside the console flows vacuum to the pods based on the buttons depressed and if it is heat or cold. If all else checks out as mentioned above, this can be an issue electrically opening and closing the pods. Sometimes the PBU/CCU is also the issue to the solenoid to allow vacuum to flow.

 

[gerryvz]

He's saying the air is slow to heat up and emit, and then turns lukewarm. This indicates to me that the hot water is not being pushed through the system and being picked up and radiated. At low car speeds/idle, it is the function of the aux coolant pump to circulate hot coolant through the HVAC system so that heat is provided.

He confirmed that the engine is running at proper temperature, and this means that coolant is reaching the proper temperature. To me, that would (generally speaking) rule out both the thermostat and the water pump.

If I remember correctly, did not all V-8 W124 models (definitely the .036) maintain the early-style, "separate" aux coolant pump and monovalve setup, whereas pedestrian W124s migrated to the integrated monovalve/pump setup sometime around the debut of the 1992 model year?

This would also make sense if the monovalve was replaced, because if it was the integrated unit, then the aux coolant pump would likely be working. But if it is a separate pump and monovalve, and the monovalve was replaced, the aux coolant pump likely was not replaced.

 

[gerryvz]

You can test the aux coolant pump by applying 12 volts to the terminals (use a car battery) and see if it runs, or not.

 

[gsxr]

If I remember correctly, did not all V-8 W124 models (definitely the .036) maintain the early-style, "separate" aux coolant pump and monovalve setup, whereas pedestrian W124s migrated to the integrated monovalve/pump setup sometime around the debut of the 1992 model year?

Almost all 124's have a separate monovalve (or duovalve), and aux pump.

The exceptions are a handful of late USA models which have the integrated valve+pump setup. These are all years with M104 HFM engines, and very late production (mostly facelift) diesels.

 

[Jlaa]

@kiev ---- good advice from @gsxr and @gerryvz. I had an issue with the aux coolant pump as well at ~65,000 miles and 23 years. Here --- Noise from center of AC-unit | Heating and Cooling The issue manifested itself in somewhat weak heat @ idle and some very faint clicking. The faint clicking was the sound of the pushbutton HVAC cycling/resetting because the aux coolant pump electric motor had seized, thus causing too much current draw.

I remember at the time that the most cost effective source for a BOSCH aux coolant pump at the time was from Amazon. I replaced the pump in 2016 and my car has had plenty of heat ever since.

 

[Kyiv]

Drove the my son to a daycare. 26 mi roundtrip. Now that I know of and kind of understand how auxillary water pump works, it indeed seemed to be the case that when driving briskly, there is more heat coming out. I will test the pump. At under $80 for a Bosch unit it's not a stressful failure

@gsxr, the air comes out from correct vents. A/C from all 4, heat only from corner ones

@Jlaa, did not paid attention to presence of clicking. My 2.5 year old is constantly talking to me though outthe drive

 

[Seangbadee]

Almost all 124's have a separate monovalve (or duovalve), and aux pump.

The exceptions are a handful of late USA models which have the integrated valve+pump setup. These are all years with M104 HFM engines, and very late production (mostly facelift) diesels.

I just reinstalled my radiator after completing work on my pulleys and related bearings, including the alternator upgrade. My engine appears to be running a bit hotter than normal, and the cabin air is not getting as hot as it used to.

I noticed that with the AC on it brings the temperature down a bit.
Prior to working on the car, the temperature was always sub 100.
What am I missing here?

 

[gerryvz]

The A/C is going to have the low speed of the fan on pretty much all of the time, drawing air through the radiator and condenser. That's probably why things are a bit cooler when the A/C is running.

That temperature is normal if the car is sitting at idle for a couple of minutes or longer, or if you are in slow traffic. If you are driving (moving), it should not be at that temp. That temp would not bother me though, in normal driving, particularly on a hot day.

Does the high speed of your fan kick in when the needle gets to 105C or higher (a bit above that mark)?

Has your thermostat been replaced?

 

[Seangbadee]

A new thermostat is on it. I haven't driven the car around yet, but it just hit me. I haven't put the fan shroud back on!

 

[gerryvz]

A new thermostat is on it. I haven't driven the car around yet, but it just hit me. I haven't put the fan shroud back on!

That's dielectric- !!

 

[Seangbadee]

That's dielectric- !!

With the fan shroud back on, the temperature has dropped, and the cabin air is hot again


Problem solved!

 

[Kyiv]

How does fan shroud affect hot air "production" in HVAC system?

 

[gerryvz]

The fan shroud directs the incoming air to the radiator and condenser with best efficiency.

 

[gsxr]

How does fan shroud affect hot air "production" in HVAC system?

It doesn't affect heater output, which is directly proportional to engine temp (assuming the rest of the system is working as expected). If heater output varied with or without mechanical fan shroud in place, it was likely a coincidence.

 

[Seangbadee]

It doesn't affect heater output, which is directly proportional to engine temp (assuming the rest of the system is working as expected). If heater output varied with or without mechanical fan shroud in place, it was likely a coincidence.

Agreed. I believe that eliminating the trapped air in the system improved the heater output.

 

[Seangbadee]

The fan shroud directs the incoming air to the radiator and condenser with best efficiency.

I drove from Atlanta to North Carolina today at about 80-85 miles per hour. External temperature was in the low 80’s and the car temperature remained below 100, even when idling.
Would you agree that things are working normally? Take a look at the picture and let me know.
Thank you

 

[nocfn]

appears normal for those RPM's and speed. How far was your walk to the gas station?

 

[gerryvz]

That is a perfect temperature, and exactly where you want things to be.

If your ambients were say, in the low to mid 90s, I would expect your temp to be ~90-92C (still well below the 100C line). Or if you were going up hills or putting a load on the engine, it would not be unusual to be in the 90-95C range (again, still well below the 100C line).

If you are interested, this is how my G-wagen (3.2-liter M104) was running a week ago. Hard to see, but it was an 86F ambient temp. Right at the 90-92C Mark. I’m 100% good with that.

 

[Seangbadee]

appears normal for those RPM's and speed. How far was your walk to the gas station?

I drove 17 miles from the time the light went on, but surprisingly it only took 15.9 gallons to fill her back up b
I was pushing it to use as much reserve as possible just to see how many highway mpg’s I could get after a fill/up. By the time I got to a gas station in Burlington they were closed

 

[Seangbadee]

That is a perfect temperature, and exactly where you want things to be.

If your ambients were say, in the low to mid 90s, I would expect your temp to be ~90-92C (still well below the 100C line). Or if you were going up hills or putting a load on the engine, it would not be unusual to be in the 90-95C range (again, still well below the 100C line).

If you are interested, this is how my G-wagen (3.2-liter M104) was running a week ago. Hard to see, but it was an 86F ambient temp. Right at the 90-92C Mark. I’m 100% good with that.

View attachment 111543

Your G -wagen has ‘baby miles’ !
It feels really good to know the hard work finally paid off.
My fans ‘kick in’ at about 100.

 

[gerryvz]

Yep, my G-wagen's high-speed fan kicks in around 103-104C indicated. For a long time the temp sensor for it was borked, and the high speed would not turn on. Diagnosis found that a sensor replacement solved the issue.

You can pretty easily go 40-50 miles after the yellow triangle turns on. You've easly got 2+ gallons at that point in time.

Look at the difference in RPMs (due to gearing) between your car and my G-wagen. I'm turning a lot higher RPMs than you at a slower speed. The drag from the AWD on the G plus its 5,000+ lb weight, also precludes me from getting more than 12-14 MPG. If I get to 300 miles per tank-ful of gas, I'm well into the yellow triangle. I could probably go 330-340 miles MAX. I typically fill up around 270-280 miles, right when the yellow triangle starts flickering.