AC question on my 86 300SDL..... - PeachParts Mercedes-Benz Forum

Hip001 · #1 08-17-2009, 09:03 AM

Disclaimer: I'm not a AC mechanic so please keep this in mind. I'm just wanting understanding for future reference.

The AC was working fine last week untill while driving home from work In a VERY hard rain almost to my house the AC just stopped blowing cold. There was standing water(puddles 1-3" deep) that I drove through on my way down the highway (US1) about 1/2 mile from my house but nothing I thought was out of the norm for a Florida afternoon. I wondered if my belt was slipping or clutch got wet or something along those lines. (I could not tell if the compressor was on or not at this point due to the pounding rain). So I cracked the windows got it to the house and parked it. I took it to my "non-mercedes mechanic" for him to put the gauges on it. It was low but prob just 1/2 can. The compressor was running and the lines felt cold all the way into the cabin. This is where he was at a loss. (Yes it will be going to Pierre this week) I noticed on the way home it would not change temp at all with the climate controller set to hot or cold. As I said I'm not a mechanic so forgive my terminology, but wondered if there was something like a "blend door" that controlled the amount of cold/heat into the cabin of the car?
Thank you for any help/information you can lend here!!
Hip

TX76513 · #2 08-17-2009, 09:08 AM

Couple of questions: Is blower working? Where is air coming out?

Hip001 · #3 08-17-2009, 09:20 AM

Yes blower working at high and low speeds.

Air coming out of center vents seemingly normal.

TX76513 · #4 08-17-2009, 09:32 AM

Take a look at THIS thread on the forum and see if it helps. I am making some assumptions that your mech checked high/low pressure and all the basic stuff.

Brian Carlton · #5 08-17-2009, 09:34 AM

Quote:

Originally Posted by Hip001

I wondered if my belt was slipping or clutch got wet or something along those lines.

Bingo.

When the belt slips.........ever so slightly.........on the ac pulley due to water, the Klima shuts down the compressor.

All will be well when the pulley is dry and the vehicle is shutdown and restarted.

Of course, this always happens at the least opportune time..........heavy rain/humidity with high ambients...........you're basically........hosed.

Hip001 · #6 08-17-2009, 09:43 AM

Quote:

Originally Posted by Brian Carlton

Bingo.

When the belt slips.........ever so slightly.........on the ac pulley due to water, the Klima shuts down the compressor.

All will be well when the pulley is dry and the vehicle is shutdown and restarted.

Of course, this always happens at the least opportune time..........heavy rain/humidity with high ambients...........you're basically........hosed.

Ok that is good info but in my case it did not come back to life the next day.

I'm looking at the other tread Tx76513 listed. It's talking about a mono-valve and I hope this is a simple fix like they are talking about.

Brian Carlton · #7 08-17-2009, 09:50 AM

Quote:

Originally Posted by Hip001

Ok that is good info but in my case it did not come back to life the next day.

Too coincidental to be searching for other control problems. Pull the Klima and jump sockets 5 and 7............see if the compressor starts and runs.

Hip001 · #8 08-17-2009, 11:28 AM

Quote:

Originally Posted by Brian Carlton

Too coincidental to be searching for other control problems. Pull the Klima and jump sockets 5 and 7............see if the compressor starts and runs.

Without even jumping the pins, the compressor comes on but no coolness from the vents.

Brian Carlton · #9 08-17-2009, 12:40 PM

Quote:

Originally Posted by Hip001

Without even jumping the pins, the compressor comes on but no coolness from the vents.

Are you positive you understand compressor rotation and the lack of rotation when the engine is running?

If so, then put a set of gauges on it.............although highly unlikely, maybe two separate and distinct problems occurred at the exact same moment in time.

Hip001 · #10 08-17-2009, 01:49 PM

Quote:

Originally Posted by Brian Carlton

Are you positive you understand compressor rotation and the lack of rotation when the engine is running?

If so, then put a set of gauges on it.............although highly unlikely, maybe two separate and distinct problems occurred at the exact same moment in time.

With the hood open I can see the AC clutch is engauged and the compressor is turning. My mechanic had his gauges on it and said it all appeared to be functioning properly. But still no cold air inside the car.

Brian Carlton · #11 08-17-2009, 01:58 PM

Quote:

Originally Posted by Hip001

But still no cold air inside the car.

See if you can get cold air on the first start of the morning...........before the engine warms...........if so, the monovalve is not fully closing.

tangofox007 · #12 08-17-2009, 02:02 PM

Quote:

Originally Posted by Hip001

The compressor was running and the lines felt cold all the way into the cabin. This is where he was at a loss. (Yes it will be going to Pierre this week) I noticed on the way home it would not change temp at all with the climate controller set to hot or cold.

If the air is fairly warm, it is possible that your monovalve has a bad electrical connection and is allowing coolant to flow to the heater core. If that happens, the heat will overwhelm the cooling capability of the a/c and you will get warm air, regardless how how well the a/c system is working. Since the temp is regulating by modulating the monovalve, attempts to regulate the temp will not be effective.

You might try clamping or plugging a heater hose.

Hip001 · #13 08-17-2009, 02:10 PM

Quote:

Originally Posted by tangofox007

If the air is fairly warm, it is possible that your monovalve has a bad electrical connection and is allowing coolant to flow to the heater core. If that happens, the heat will overwhelm the cooling capability of the a/c and you will get warm air, regardless how how well the a/c system is working. Since the temp is regulating by modulating the monovalve, attempts to regulate the temp will not be effective.

You might try clamping or plugging a heater hose.

Oh wow, Good Call Tangofox! I'll try that when I get home! Should this happen to make a difference, where is this "monovalve" to which you speak on 1986 300SDL?

Again I am not a mechanic or AC expert but your comment makes sense because the temp did not change when I adjusted the dial. Is this monovalve vacuum controlled cause the vents did not change either when I pushed the defrost button.

brandlj · #14 08-17-2009, 03:00 PM

The monovalve sits on the firewall inboard of the battery, next to the ABS computer. It is not Vacuum controlled, only electronically controlled. When you pressed the defrost button the vents did not change? That is pointing to a CCU ( climate control unit) fault. Something electrical may have happened with your car. Have you checked all of your fuses in the fusebox? Have you checked the 10Amp fuse on top of the OVP? That is the Over voltage protection unit which sits on the driver's side of the firewall next to the KLIMA relay. Do you have any dashboard lights on while you are driving, specifically the ABS light?

daw_two · #15 08-17-2009, 03:01 PM

Quote:

Originally Posted by Hip001

Oh wow, Good Call Tangofox! I'll try that when I get home! Should this happen to make a difference, where is this "monovalve" to which you speak on 1985 300SDL?

Again I am not a mechanic or AC expert but your comment makes sense because the temp did not change when I adjusted the dial. Is this monovalve vacuum controlled cause the vents did not change either when I pushed the defrost button.

EDIT --- I see brandlj and I were posting at the same time.

Now, Hip001, we all understand that you are not an AC expert, but I know you do not have a 1985 300SDL.

Your typo is forgiven.

The monovalve "rebuild" kit is easy to replace. I did it. If you are standing on the passenger side of your car next to the battery, the monovalve is toward the driver's side looking over the battery. If memory serves me correctly, you don't have to remove the entire valve (it's a boxy kind of looking thing with 2 rubber coolent hoses and an electrical connection). You can unplug the electrical connection and take the 2 screws (do NOT drop) out of the top. The thing "pops" open (is there a spring in there? I don't remember). Inspect the diaphram on the top of the brass looking shaft --- It probably has a tear in it. Coda's did.

Anyway. Remember how the thing fits together. Take the thing apart with all the parts lined up. I think the rebuild kit comes with a shaft and new diapharm on it. Put all the parts back together.