126 heater blows cool intermittently - PeachParts Mercedes-Benz Forum

cdunn@u.washing · #1 02-18-2006, 12:54 PM

The heater on my 91 300 SE with 80k blows cool air intermittently with engine fully warmed up. Fan blows fine, but air is cool sometimes. Engine temp gauge reaches just under 80C when fully warm. The monovalve was replaced 35k ago by the former owner. Could the thermostat be sticking intermittently?

stevebfl · #2 02-18-2006, 01:15 PM

Quote:

Originally Posted by cdunn@u.washing

. Could the thermostat be sticking intermittently?

Is the engine temp cold intermittantly?

Do You get heat if you turn the temp wheel to "max"?

cdunn@u.washing · #3 02-21-2006, 09:38 PM

Quote:

Originally Posted by stevebfl

Is the engine temp cold intermittantly?

Do You get heat if you turn the temp wheel to "max"?

Steve: yes, I get heat if I turn the temp wheel to "max", but te engine always heats up to just under 80C. This morning, before engine was fully warmed up (after 5 minutes), heater was working fine (blowing hot air) but 10 minutes later, by which time engine was at just under 80C, the air became tepid. hmmm...

raymr · #4 02-21-2006, 11:58 PM

Is air getting sucked in through the temp sensor?

cdunn@u.washing · #5 02-22-2006, 07:54 PM

not sure. How do I find this out?

Nipperiley · #6 02-23-2006, 02:40 PM

I had the same intermitent heat problems with my 1991 300SE. 145Kmiles.
I replaced the monovalue diaphram (Old one was torn) with a new monovalve rebuild kit ($45 approx). Heat is now great. I do not know how long those valve diaphrams last, it looks like rubber from a tire innertube. The job only took about one half hour.

raymr · #7 02-24-2006, 11:56 AM

Quote:

Originally Posted by cdunn@u.washing

not sure. How do I find this out?

Theres a tiny grille on the dash or ceiling with a sensor behind it. There should be a small amount of suction that you can test with a piece of tissue paper. If theres no suction you need to check the sampler fan behind the dash.