blower quit, only hot air from vents - PeachParts Mercedes-Benz Forum

reddirtranch · #1 08-31-2006, 09:41 PM

The other day after I drove home without the AC as its been cooler. I got n my 91 300TE the next morning and noticed my AC Blower didn't blow. I had replaced the motor and regulator last spring.

Today, I noticed that there was hot air coming through the vents, passively since the fan doesn't work, even if the thermostat is set to 65.

Does this sound like the "buttons" , anyone ever experience this ? I'm puzzled about where to start.

any suggestions/pointers/links to threads etc are greatly appreciated

Thanks

lee polowczuk · #2 08-31-2006, 09:49 PM

check fuses...including the blower strip fuse that's in its own black box on the drivers side near the strut mount...

you could have blown the fuse that controls the heat valve...it's happened to me... same effect...

reddirtranch · #3 08-31-2006, 10:08 PM

Thanks, I checked fuse # 7 and jumped the fuse by the strut tower with a test clip . This may have solved my problem with my 87 300TD but didn't seem to help the 300TE.

thanks, I'm still searching.

cdplayer · #4 08-31-2006, 11:00 PM

I have a 1984 500 SEC. Blower went out too. Not fuze but blower resistance group. Not sure of your location but may be same as mine. On the driver side in the engine compartment under the brake master cylinder (you may need a flash light) is the resister group. A small metel box with holes in it (like swiss cheese). Inside the box a series of springs (or resistors) My problem is debris had collected in and around the box and caused the resistor to over heat. Wires got melted. Hard to work on but a little patience and you can get it out. Bought a new group, and blower moter at Rusty's. Works great now.

david s poole · #5 09-01-2006, 12:11 PM

blower has separate fuse under hood in rectangular black box.it has flat 30amp fuse each end held by machine screw.check for crack in the middle or burned out.compressor should not start if no blower.

reddirtranch · #6 09-01-2006, 03:44 PM

Thanks, the fuse check ok. even when in econo mode set @ 65 degrees, there is HOT air coming from the vents when crusiing. It was 68 degrees this morning and there was heat coming from the vents, the temp guage was just above 80. ie normal running temp. I'm stumped. Heater Control Valve?

Thanks

pmizell · #7 09-01-2006, 05:04 PM

Sounds like your push button control unit has gone South. Lot's of info in the archives on this topic. Over time a solder joint or two goes bad on the PBC circuit board -- if you're OK with soldering you can pull it and try to spot the bad joint or re-solder all the main joints. You can also buy a remanufactured unit ... try Fastlane.

You can test the output values of the PBC at a 3 pole connector right next to the brake booster. I think the colors are yellow, red and black. If you get the same resistance value for all 3 wires (high fan, low, off) then you know the PBC is shot.

If your blower motor, regulator and fuse are all OK I'd wager that this is exactly your problem.

Good Luck

reddirtranch · #8 09-02-2006, 06:20 PM

Thanks for the tip, it's not the buttons. I am fortunate enough to have a parts car to swap with. The buttons work in my other car and those do not in my 300TE.

I tested the resistance between the three terminals and either I missed the connection or there is no continuity. I'll check more carefully tomorrow.

Thanks!

Ron in SC · #9 09-02-2006, 06:31 PM

If you have a spare monovalve, that you're sure works, I'd swap them out and see if that's the problem.

reddirtranch · #10 09-03-2006, 01:23 PM

I checked the monovalve with an ohm meter, the one in the car in question measured as open, the one in my parts car measured 3.5ohms. Not sure what is proper resistance is. I sawapped them and I'm still getting warm air out of the vents.

As far as the fan, I suspect the regulator, I put a new motor in but a used "porcupine" last year, I'll swap that out tomorrow.

Gotta love these things, park the car one evening and everything works, get in the next morning and something doesen't....sunroof, blower, I wonder whats next.

Ron in SC · #11 09-03-2006, 06:09 PM

The voltage to the monovalve should be at least 11 volts and the resistance should be between 11 to 19 ohms.

I had a problem with heat coming out all the time too. I tested the mono valve in question and it measured the proper resistance. I still thought it was the mono valve so I took it apart and the little diaphram inside was busted and coolant was going where it should not go. The monovalve was the problem.

I took the mono valve out of my 92 300E and put it installed in the 92 300TE after removing the one I took apart. The monovalve was the problem, even though it had the right resistance.

I suggest you take one of the monovalves apart and I think you will be able to push the little brass valve thing (for lack of a better term) inside down to keep it in place, that way hot coolant will not get to the heater core in the evaporator box.

think300E · #12 09-04-2006, 02:20 AM

I had a similar problem. Hot air coming out of window vents and hot air coming out of defroster vents all the time. Fuse looked fine, I just suffered like that for a while.

Last week I decided to tackle the issue. Read about testing the monovalve.
I was advised to turn the key to the on position car running or not and unplug the monovalve to see if i could feel a click, i didnt feel a click, but it was pretty hot. Tried to measure resistance for the monovalve, but I may have done it wrong.

I have a small multimeter from Sears. Set to Ohm 20k (changed from 20M to 200 - trying to get a reading), cross neg/pos get zero, place the neg/pos terminals on the monovalve two connection terminals and get zero (so I guess I am doing it wrong - cannot tell what the resistance is) however then used it to test the voltage of the connector that plugs into the monovalve and it was zero too. (i guess i was able to use it fine for that).

Turns out fuse #7 had a tiny crack which i guess i missed - replaced it and no more hot air (ac doesnt work - different issue). Tried to test the monovalve again, still couldnt hear it click and was not able to get any different results with the multimeter, but no more hot air.

What does open mean? does open mean zero?

Any pointers on how to utilize the multimeter? Maybe i was doing it correctly?
http://froogle.google.com/froogle?q=sears+multimeter+82082&hl=en&lr=&sa=X&oi=froogle&ct=title

Thanks

reddirtranch · #13 09-04-2006, 08:34 PM

thats some good info, I'll try that. I believe on a digital multimeter that 0 is a dead short, infinity would be open. I miss the analog meters of my youth

I didn't get around to the parts swapping today but I'll replace #7 just on principle. Thanks for the tip on the fuse crack.

Thanks

reddirtranch · #14 09-09-2006, 04:26 PM

I changed the regulator. still no fan. I can put 12V to it and get the fan to spin, probably not a bright idea. Is there another relay somewhere ?
I can't seem to find the resistors or don't know what I'm looking for
Thanks