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1982 Mercedes 300TD wagon
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1,057 Posts
Discussion Starter · #1 ·
Does your a/c unit seem to blow cold then back off a little then cold again? My car seemed to cycle this way my entire trip. I found that if I turned the a/c off for a moment then back on the air came out crisp again. Is this normal or is my control module acting goofy? I'm really putting my car to the test over the last 24 hours!
 

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76' 300D
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24 Posts
Air-Squirrels

Benzoid,
Same prob w/mine - only worse. Some kind of "vacuum problem" w/mine (76' 300D w/70K) I jsut bought the car 15 days ago and am discovering the balanced joy of an MB. One family car, quite well taken care of w/ a new compressor last year. Blows plenty cold when it blows.
Basically will start as soon as I hit the fan switch and blows cold & fine until I hit about 40mph. Then it mostly "dies" and stays dead (usually) until I come to virtually a complete stop, and starts blowing cold and strong again! If I keep it to just below 40 (I'm mostly in the city), it just stays on fine.
The other major screwy thing this MB does is it usually will not start (does turn motor over) w/in 15-20 minutes of being shut off UNLESS I lock/unlock the doors, and step on the brake (doing something to the vacuum). It will then start!
I've notices occasionally some really squirrelly "air sounds" emenating from in the central-right dash - not contineously but occasionally and quite unusual. The pup's 30 years old and has been a Houston Texas girl all this time, and buddy it gets HOT around here in the summer. Haven't had much chance to check lines and would much appreciate anyone's advice on this. Hope it helps you Benzoid.. P'3
 

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76' 300D
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Benzoid, does your fan speed die-off too, or just the temp of the airflow (and waht was your year)? And thanks Washerman for the tip. I assume the "low freon was for Benz, and the switch thought was for my 76' 300D? Would a 76 have a switch, and where might it be located? Thanks, P'3'
 

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1984 300CD, 2015 Sprinter 3500, Coach House Platinum II
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2,722 Posts
Fix the AC for GOOD!

Here 's a sure fire way to fix your AC. It's not OE but will work on any vehicle.
 

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83 300 d t
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all ac systems have a switch to prevent compresser from runing on low freon or no freon if the level is low the switch will switch clutch on and off about every 1 to 10 minutes plus the hoses will ice up .if there is no freon the switch will shut the clutch off completely. i would think the switch is conected on the hose line by the dryer. my compresser is hang the old owner left it this way i have alot of work to get my climit control to work i wish i just had a low freon level i can not even get my fan to turn on . well it turned on once and all i had was full heat.
 

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1982 Mercedes 300TD wagon
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1,057 Posts
Discussion Starter · #8 ·
No, there's nothing goofy with the climate control box. The flow of cold air feels like it comes in bursts of icy cold then almost back to vent then back to cold. Perhaps it's normal for the car to do this in order to keep the system functioning properly. I don't think I'd notice it as much if the air blew out of where it's supposed to instead of clinging to the single side vent for relief! It did what it needed to do for the trip so it only can improve from this point! I have a feeling this is going to be an expensive repair though! It will have to come AFTER I pay for my miserable dental proceedures now and in the near future. I hate when "neccessity" overcomes "entertainment" and "toys"!
 

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83 300 d t
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699 Posts
what kind of freon are you running you can try to shoot a can if it is 134 this cost about5 bucks this will stop the cold burst this is usaly caused by compressor clutch turning on and off not by climit controol issue. i had this problem in many cars and 1 or 2 cans of freon fixed it .
 

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Does the compressor cycle on and off during these periods? If the ETR switch for the evap is bad, it can cause these problems. The ETR switch cuts power to the compressor if the evap gets too cold, preventing the evap from icing up. The compressor will cut back on once the ETR switch decided the evap is no longer frozen.

Jamie
 

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1982 Mercedes 300TD wagon
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Discussion Starter · #11 ·
To be perfectly honest, I don't know if the compressor has been turning on and off. I just feel a decrease in coolness every 5 minutes or so. It's probably a natural function of the system. The freon is probably the new safe kind and I had it recharged fully almost a week ago prior to the trip (and thank God I did!).
 
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