Does the air conditioner and blower operate, although there is no heat?

[arjun_wilsonu]

Please help me figure out why my heater is not producing sufficient heat. Because the air conditioner is turning on and blowing chilly air, we may assume that the temperature dial is also functional.
Does anyone have any simple ideas?


(5) in 1986

[gabriel_parkeru]

Monovalve is probably not a good choice. You may find a plethora of instructive films here. If the monovalve is the culprit, this is a simple remedy.

[arjun_wilsonu]

Unfortunately, I have not been able to locate a comprehensive video tutorial on how to fix this issue. According to what I've read on the forums, though, a broken monovalve would make the heater run continuously at maximum power. Does a broken monovalve also not produce any heat? A video on Mercedes Source demonstrates how to use a 12v power source to test the aux water pump. How can I check the integrity of the monovalveand/or the wiring that leads to it? Both of these components are probably the most typical culprits, in my opinion.

[danielrq]

To test if the heat returns after disconnecting the monovalve, try turning it off and then back on again. Although it is wired to close, the monovalve is normally open. The presence of heat indicates that there is an issue with the control system.

The monovalve plug contains two wires; the system opens and closes the valve based on the brown wire, which is ground. The second one is a hot 12-volt power source that is always present when the key is turned on.

[gabriel_parkeru]

Heat might remain on or off if the monovalve is malfunctioning. Although my car's fan and air conditioner were operational, the heater was not. Now the heat works well after I installed a replacement kit for the monovalve. If you search YouTube, you'll find several videos that explain the process of replacing. You may find it on the engine firewall, on the passenger side.

[arjun_wilsonu]

Here is my present state of troubleshooting, which has not yielded any results thus far:
1. Even after disconnecting the monovalve, there is no heat.
2. Am I testing this properly? When I turn on the key and use my automated multimeter, I measure resistance in Ohms (~20) across the two plug wires that go to the monovalve, but I don't see any voltage. After that, what comes next? Could the problem be with the temperature control wheel in the dash, or is there a relay or fuse for this?

3. Does the aux water pump require a 12V supply for testing? Is it the object with the monovalve and the firewall in its vicinity?
4. On a side note, the foam tube beneath the glovebox is not insulated, but I gather that this just impacts the automated temperature control sensor and not the heat's actual performance.
I would really appreciate any more instructions you could provide.