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Discussion Starter · #1 ·
1991 Mercedes 560SEL w126. No Heat. Monovalve replaced. Auxiliary pump working. Vents & blower working. Cabin sensor working. AC works. Is there a fuse and/or relay for the heater core? what is the fuse or relay location and how does one access the heater core? Winter's coming!
 

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Monovalve replaced.
With what? Most after market monovalves are not worth the trouble.

Do you get any heat at all? Monovalve issues often present when driving but not when idling.

Put your hand on the hoses going to the heater core. Are they hot?
 

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1991 Mercedes 560SEL w126. No Heat. Monovalve replaced.
Hey Neil, Welcome to BenzWorld!

John brings up good points above, especially in regards to “Monovalve replaced”.

If you replaced the insert complete with metal barrel, screen & rubber diaphragm etc. and that part was inexpensive [say, less than $175 or so] then it won’t deliver the heat you need above say 25 mph on the road.

If that above was the case, I hope you saved the original MB one as it can be rebuilt using a repair kit by URO. Easy-Peasy.

As there is no data as to how/when the heat fails I offer this as the most likely scenario.

Good luck,

MBL
 

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Discussion Starter · #4 ·
Hey Neil, Welcome to BenzWorld!

John brings up good points above, especially in regards to “Monovalve replaced”.

If you replaced the insert complete with metal barrel, screen & rubber diaphragm etc. and that part was inexpensive [say, less than $175 or so] then it won’t deliver the heat you need above say 25 mph on the road.

If that above was the case, I hope you saved the original MB one as it can be rebuilt using a repair kit by URO. Easy-Peasy.

As there is no data as to how/when the heat fails I offer this as the most likely scenario.

Good luck,

MBL
Thank you John & MBL for responding. I ran test by unplugging the monovalve, which should then be in an open position as it only closes when activated. Still no heat whatsoever.
 

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With what? Most after market monovalves are not worth the trouble.

Do you get any heat at all? Monovalve issues often present when driving but not when idling.

Put your hand on the hoses going to the heater core. Are they hot?
With what? Most after market monovalves are not worth the trouble.

Do you get any heat at all? Monovalve issues often present when driving but not when idling.

Put your hand on the hoses going to the heater core. Are they hot?
Thank you John & MBL for responding. I ran test by unplugging the monovalve, which should then be in an open position as it only closes when activated. Still no heat whatsoever.
 

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Most aftermarket monovalves do not work reliably regardless of whether it is activated or not.

What brand of monovalve did you replace it with?

If the old one was original MB, I hope you didn't discard it.
 
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