I've been searching quite a bit on this topic and I seem to be just spinning wheels. I have no heat in my car (also don't have AC but one thing at a time). This is a Klimatronic unit.

Things I've tested/replaced so far:

• new thermostat and senders (not really relevant other than to say engine is idling at 80* C)
• 5 of the 6 valves on my tree of six weren't working, so that was completely replaced. Tested and all valves now fire.
• vacuum at the tree of six is 19 mm Hg so good vacuum
• tested all the vacuum (mightyvac) actuators, 3 appear to be working
• replaced the fresh/recirc actuators (both of them; 5 & 6 in photo below)
• need to find a vacuum leak (possibly replace) on the defrost vent which I'll tackle at a later time, i believe number 4 in photo below.
• Additional testing on the center vent which I believe is number 3 below.
• replaced the monovalve
• I do have voltage at the valve when the heater is on
• I can feel heat on the inlet and outlet side of the heater core in the engine bay

Now the issue, just no heat. Drove into town yesterday and it was about 50 outside. Engine was up to temp so I put the heater to 26* i was getting cold air (outside temp, not AC cold) out of the vents.



My question: do I suspect the heater core and start looking at replacing that or is there a, what I call, blend door that may be suck in the AC direction? How do I check the actuation of this blend door? Does the blend door typically fail in the AC position?



I've been referencing these two photos. I've been assuming this relationship (please correct me if I'm wrong):
38 valve is number 4 (only valve with 2 inlets)
39 valve is number 2
40 valve is number 3
therefore 41 is number 1








The photo below is from a class 2 W126 so it has the tree of seven which doesn't have the orifice between 40 and 38 like the class 1. Also uses a different foot valve but that's not relevant. But it would seem logical that 41 is the blend door (diverter flap?) to which I reference. Am I baseless in my assumption? If so, I would think 41 in the above photo would also be the blend door. Which would lead me to believe valve 1 in the photo is where I need to look. I'm confused by the 1985 service manual which calls 41 a "scoop air flap". Does "scoop air flap" mean diverter valve (blend door)? If so, I think I need to focus some attention there.








Do I need to focus any attention on temp sensors? Right now I'm using the extremes of the temp setting (high heat until click) so I would think the temp sensors are being 'ignored'.

The monovalve is controlled by a grounding system through the computers, not with
12volt positive, unplug and see if there is heat.

Unplugged the monovalve on my drive into town today. Same result, just outside temp air blowing regardless of temp/vent/fan speed settings.

Yes, diverter valve, located just above throttle pedal and inward. Apply vacuum on vacuum
line and hear if door moves. If upper kick panel is removed can access, possible arm has
come off.

You should feel some heat. The car is designed in a way that in failsafe mode there is heat for the window at the very least. My guess is your climate controller has an issue and is commanding for no heat. For example there is a thermistor input for the climate control and if it is shorted it’ll will think the temperature is already very high and shut down the climate control.

Or maybe the CCU has a broken solder joint. This is most likely. Or the switch in the temperature wheel is grubby - this shorts out the potentiometer and commands for full heat when you max out the thumb wheel.

I’d start by pulling the CCU and tearing it all down. Resolder all the joints with fresh solder. If you don’t feel comfortable about doing this, find somebody to rebuild it. We used to have lots of guys here who’d do it for you for a reasonable fee. Or trade it in for a rebuilt from Programma. I like that option least but it is a way forward.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Just a few thoughts.

Have you checked Defrost Mode at the front windshield? If you are getting heat in and out of the heater core then you should have some heat, Defrost would be a good check.

Also Pod#40 has a physical rod connection between it and the center vents, the pod may be bad, or the rod was not connected. The thumb wheel on the center vent controls the upper flap, and the underside of that has a metal rod attached to the lower flap on the heater core to divert air to the center vents or the defroster. If this has been worked on in the past, something may have been left disconnected.

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

It would be good if you can use an infrared thermometer to tell if the heater core is getting hot. Is there any place you could get a reading on the core? Are the hoses hot going to the mono valve? If the core isn't getting hot then it isn't likely there is a control side problem.

Monovalve failure causing no heat is common and some aftermarket valves had their share of problems.

If the hoses to the monovalve are hot and the hot water is going through the valve into the core, I'd try CRC ThermoCure flush and give it plenty of time to work. ThermoCure can only be used with pure water, no coolant. The engine must be protected from freezing while using it.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

what year and model is your car?

1985 300 SD CA edition.

I've done a bit more tear down and diagnostic. I do have a small vacuum leak on the "scoop air" control line which I will address. However, the valve itself is working. So far I've been able to verify/correct functionality on the tree of six as well as all the valves sans the above mentioned leaking line.

Unfortunately the answer to most of the above questions is no heat at all. I can feel hot water going to/from the monovalve in the engine bay but there is just nothing coming from the heater core. When I had the interior side panels off I was able to reach my hand into the heater core area through one of the foot vents and it's not even warm to the touch. In all my readings (and mentioned above) I've come to expect buckets of heat as the fail safe but I have nothing.

It is outside temp air which has me wondering if the heater core is plugged (internal/water side or rat's nest in front), something is causing all the air to bypass the core, or something is commanding it off entirely. I'm comfortable enough taking out the CCU and soldering, that shouldn't be an issue. I may just purchase a refurb as the little icons and color wheel are gone/worn. I'll see if the manual has specs to test the thermisters in the air box.

I do have a laser thermometer, i'll see if I can get some readings at different points around the heating system.

Need to ck water flow. When unplugging mono valve, water flow goes to full. Be sure to
test check valve under mono valve, to test remove mono valve, use a straw to push
down on ball valve, has a very light spring under, hold straw very lightly and feel if spring
pushes ball back up, can cause heating problems if I remember correctly.