We've started using AC in Arizona in last couple of weeks. Most of the times, the AC works fine, but every 2 or 3 days, it will suddenly blow out hot air for a long time. The next time I drive the car, it's OK again, blowing out cold air.
What parts do I need to check for this erratic behavior?
Thanks.
David 83 300 DT

Check the foam tubing that runs behind the glove compartment. If there is none, then you need to replace it. Some say using pipe insulator from the hardware store will work, I tried it, it didn't work for me. The only thing that would work for me is the OEM part. It's a bit more than the cheap stuff from the hardware store, but it's whats SUPPOSED to be there, and it works. I don't have an exact part number right now, but it begins with 617 I'm sure. I'll get it later if you remind me.
-Joe

__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

Thanks.
I happen to have a piece of foam tube in there from Home Depot. Time to shell out for the real stuff, then.

The ACC control buttons on my 81 wagon barely acknoledged my requests for specific performance out of the Air system. It might be 10 minutes or never when it followed my selection...
In the archives there are some good write ups about checking that unit , or first check the vacuum hookups which lead to it....and check the vacuum controlled flaps which change from routing the air through the heater core to the ac evaporator box.

Time for a monovalve repair kit.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

Foam tube as used to insulate pipes works great. As Paul says, you should check the monovalve. Remove the four screws and lift up the top. If it is flooded above the diaphragm, rebuild it with a kit from the dealer or fastlane.

Good luck,

Does anyone have a digital picture of the monovalve?

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Jimmy

Look on the firewall just inboard from the battery.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

When you say "hot air," are you refering to hot ambient air or heated air? If it is just hot ambient air, there is no need to investigate the monovalve. Also, is the a/c compressor engaging during these "hot air" episodes? The intermittent nature of the problem sounds more like a control issue.
If the heater is actually coming on, check the electrical connection on the monovalve. The monovalve is electrically closed. If it loses power (ie: dirty connector), it opens to the max heat mode.

Oh. the air is really hot coming out of the vents, and the compressor is engaged whenenver this happens.
I replaced the monovalve just 2 months ago. It was suggested to me yesterday that the monovalve may be damged now because I did a radiator flush after the replacement.

Jimmy:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EH0TL2AI1HQ0N9JPA&year=1980&make=MB&model=300-D-002&category=R&part=ACC+Mono+Valve

Check/clean the electrical connector on the monovalve. A poor connection there could be the problem.

I installed a repair kit once which would intermittently stick inside the bore, that is, it sometimes wouldn't close completely.

You can bench test it. Take it out of the car and CAREFULLY apply 12 volts across the coil, blow through it and see if it seals completely every time.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

Thanks to you and Palangi. When I get my wagon back I will locate this. I'm thinking of trying to hook my ACC up, as it has been bypassed in favor to manual toggle switches. It works OK as is I guess, but I only have High speed on my fan, and AC through the front and defrost vents.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Tangofox is right about checking the monovalve connection. When the connection is open, the valve is open

Edit: Wow!! Price on a monovalve has just about doubled since the last time I bought one.

__________________
Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE