Alright... I'm getting annoyed by my car's AC. Here's the deal.. it was converted to Freeze 12 (not by me) in the summer of 2002 or 2003. From what I read from the greats like Larry Bible, this will only last a few years before something is eaten away. Does this also affect cars that have been converted to Feeze 12?

I took my monovalve out(lost 2 screws doing so ) and examined it for damage. Didn't see any physical tears in the diaghram that many posts talk about.

Now here are the symptoms.

Sometimes I get cold air when I start the car. Its not super cold.. but just "cold". After 10 minutes of driving, I notice the "cold" becomes just regular air temp. Not hot, not cold.. just "regular". Once I park the car and try to start again, I just get HOT air. I feel it coming from all vents. So at this point I just turn it off. Other days I am not so lucky... I don't even get the "cold" air, but regular air temp air coming out of the vents.

Today, I took the monovalve out to check it out. Took pictures of it and hopefully some of you experts can tell me something from the pictures.

There is no leaks of any kind on the car... dry as a bone, and that includes the compressor.

As I am not knowledgable at all in the field of AC, please be as specific as possible if there's something that I should do.

monovalve



Disassembled monovalve


Bottom of monovalve


rubber diaghram moved down


side of monovalve


monovalve with me pulling down on it


closeup of the end of the monovalve

bump..

One full day and over 100 views.. with no replies? Did I stump even the greatest DIY'ers on this forum with my post?

Here's a long shot - do you have the center vents pointing directly upward? If so the cold air fools the temp sensor near the rear view mirror and the A/C system cycles accordingly by thinking it has reached the set cabin temp. The hot air coming out after sitting doesn't surprise me, my car does that too and my A/C works fine. Could be the hot engine heating the duct work and air left in there. Never saw such a detailed set of pictures of a monovalve before. Thanks.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles

dtf, no the center ducts are pointing straight out. The adjustable levers on each vent is at maximum, as well. Any more tips.. from anyone?

Well, the monovalve rebuild kit is cheap so while you have it out just renew it. My w126 had NO heat as a symptom. That seemd to indicate the monovalve as per archives. Replaced the same and got heat back.
My w126 does not have cold air right after engine start but a bit later, so when it is hot outside I open windows until engine warms up a bit, then I can use climate control w/o getting same hot/warm air blown at me.

Does the a/c have a relay that may have burnt out?

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Let's start at the beginning.

Why are you chasing the monovalve?

My personal belief is that the monovalve has no bearing on the situation. The hot air that you feel when starting the vehicle is perfectly normal. The heater box gets significantly hotter than the cabin. I've noticed this on the SDL. Don't even bother to turn the system on unless the a/c is working. Better to just roll the windows down.

The symptoms of cold air for a short period of time and then gradually warming will be due to one of two general possibilities:

1) The compressor drops off line (a multitude of possibilities, all electrical)

2) The compressor remains on line (engaged) and there is not enough fluid in the system to do the job.

To go further, one of the above needs to be confirmed.

This can be done in the driveway. Set the temperature dial all the way to the cold stop. Operate the system at 1500 rpm and observe the compressor. It should remain engaged for the entire period of the test.

Thanks Brian for your reply. When you say "engaged" you mean "hearing it run" in simpler layman's terms, right?

I might eventually have to take my car down to an AC repair place and let them figure it out.

So what I gathered here is... the monovalve has nothing to do with my problem?

I've been reading the heat/acc related topics. I have an '85 300TD station wagon. I live in Alaska. This fall I noticed that when it began to get cold out my heater did the same. I don't have a working tach so I can't relate rpm to heat output. However in my case it doesn't put out heat at all now. Not at idle or throttle down. I cleaned the monovalve in Sept. Didn't notice any other problems other than it was dirty (a very large bug was inside-how did that get there?) however now that I'm reading all the posts I doubt I was all that thourough at inspecting the monovalve seals. I want to buy a monovalve rebuild kit, but I also want to make sure that I've identified the problem. Did you rebuild your monovalve snibbles, and if so did that work?????

AKchic: If you disconnect the power to the monovalve, you should get full heat. If you are not, then either the monovalve is stuck shut, or, your aux. pump is no longer wanting to pump. (follow the heater line to the aux pump - you can usually hear it buzzing/running with the starter key in the on position)

Snibble: I'm thinking that since the monovalve is in full heat mode with the power line disconnected (or engine off, for that matter), that the heat you are getting, is hot coolant flowing through there. Once you start the car, the monovalve closes (not sure how fast), but some hot coolant still gets by, and heats up the core. After a minute or two, you should feel cold air again. At least, that's what I am experiencing with my 300D.

AKchic: Good luck with keeping warm!

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09 Jetta TDI
1985 300D

question on the aux pump.. not sure yet if this is even the case but what if the aux pump does not turn on at all? I know my aux pump works b/c i've tested it with direct 12v pwr. what tells the aux pump to turn on? the CCU?

I too ahve a heating prob. havent chkd the monovalve yet. but this pics really help. i be chkg it and the aux pump tonight. am assuming that i will hear the aux pump running by simply turning the key on and the dial on heat.

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the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
2007 Honda Accord EX
2007 Honda Accord SE V6
96 C220
97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
80 300TD - Found Another Home
Previous cars:
96 Caravan
87 Camry
84 Cressida
82 Vanagon
80 Fiesta
78 Nova
Ford Cortina
Opel Kadet
68 Kombi
Contessa

1984 300d Turbo 146k
Replace The Monovalve And Check The 3 Washers, Install The Valve,
Small Washer, Wave Washer, Large Washer, And Aux Water Pump For
Heat At Stop Light, You Can Hear The Pump Ign On ,and To Heat, Eng Off, .5 Diy. For A/c Check The Rec Dryer Sight Glass For R-12 Flowing If A/c Compressor Clutch Is Lock You Have Some R-12, Sight
Tube If Low R-12, Check For Leaks And Recharge