A/C nightmares - PeachParts Mercedes-Benz Forum

thebenstenator · #1 07-09-2012, 07:05 PM

Hey guys, I'm having some A/C issues with my car.
First of all, I have a strange problem where the air will blow on high for a good amount of time and then it will turn off, then it'll come back on for about 5 seconds and turn off for 10 repeating the process. After doing some research I thought it might be linked to bad auxiliary fans, I replaced them but they were still not coming on. I tested them by taking out the pig tail connectors off the red pressure switch and jumping the other ends. The fans came right on with the key in RUN.
Now here's where my problem gets worse. I decided to buy a new pressure switch and when I went to replace it. . . well, you guessed it, I lost all my freon. I had just recharged the system at a shop.

Anyway, all this was caused by me trying to fix the intermittent blower. (PS the blower motor is new also, and it's weird because it will blow all day on a not-so-hot day. It's just on the very hot days when I actually need the A/C that it does this cycle).

So two questions. Now that my system is empty I'm considering converting it to the cheaper r134a myself. What would that process entail?

And more importantly, what will fix this dang blower motor problem!? I've now traded out the blower motor, the auxiliary fans and the accursed pressure switch. What else could be causing this?

qwerty · #2 07-09-2012, 07:24 PM

Quote:

Originally Posted by thebenstenator

First of all, I have a strange problem where the air will blow on high for a good amount of time and then it will turn off, then it'll come back on for about 5 seconds and turn off for 10 repeating the process. After doing some research I thought it might be linked to bad auxiliary fans, I replaced them but they were still not coming on.

The aux fan has no relationship to the blower fan. (Presumably, "blow on high" refers to the cabin blower fan.)

Quote:

Originally Posted by thebenstenator

I tested them by taking out the pig tail connectors off the red pressure switch and jumping the other ends.

The aux fan is operated by a temperature switch, not a pressure switch. Under typical conditions, the switch is closed only a small percentage of the time. Like stop and go driving in hot weather.

Quote:

Originally Posted by thebenstenator

What else could be causing this?

The blower issue sounds like a control problem.

thebenstenator · #3 07-09-2012, 08:00 PM

Control problem as in the buttons inside the car? Or control problem as in relay or something else?

thanks for the input.

qwerty · #4 07-09-2012, 08:40 PM

Quote:

Originally Posted by thebenstenator

Control problem as in the buttons inside the car?

Could be anywhere in the blower fan circuit, but the push button unit would be a prime suspect. Does the intermittent blower fan condition occur in all modes and settings?

thebenstenator · #5 07-09-2012, 09:00 PM

As far as I can tell it only occurs on the hottest of days. But I did try switching over to ec mode once when it turned off and it still had the same problem.

foolio · #6 07-09-2012, 10:28 PM

In my BMW days, this problem could be caused by the final stage resistor going bad. I don't know if the w124 has something similar.

Also, check this:

w126 erratic A/C

thebenstenator · #7 07-10-2012, 01:22 PM

ah yes, someone mentioned some sort of resistor a while back when i was having this problem. Is it available to buy? What name would I find it under?
is this is?
http://catalog.peachparts.com/item.wws?sku=W0133-1627882&itempk=86428&mfr=Beru&weight=0.35

edge · #8 07-14-2012, 09:04 AM

Quote:

Originally Posted by thebenstenator

.Now here's where my problem gets worse. I decided to buy a new pressure switch and when I went to replace it. . . well, you guessed it, I lost all my freon. I had just recharged the system at a shop.

Why would you lose your refrigerant when you replaced your A/C temperature switch? I don't think there's refrigerant pressure on that switch, just temperature.

qwerty · #9 07-14-2012, 11:31 AM

Quote:

Originally Posted by edge

Why would you lose your refrigerant when you replaced your A/C temperature switch? I don't think there's refrigerant pressure on that switch, just temperature.

Depends on the model. As difficult as is may be to believe, all models are not the same.

thebenstenator · #10 07-15-2012, 10:42 PM

Yeah I was reading about a/c probs on another thread but it was with the older models of the 300D and they were saying how you could take out the temp switch and pop it in hot water to see if it worked correctly. So i thought if they could do it on the previous model of the 300D I could at least change mine out without losing the freon. As it appears. . . not so. .
Word to all who might try this on models like mine! Don't!!!
I think I'm just gonna deal with the hot air for now. Replace the resistor to see if that helps the aux fans or the weird blower motor problem (but I guess I won't really know about the aux fans until I recharge it again. ugh)

Air&Road · #11 07-16-2012, 08:03 AM

Quote:

Originally Posted by thebenstenator

Hey guys, I'm having some A/C issues with my car.
First of all, I have a strange problem where the air will blow on high for a good amount of time and then it will turn off, then it'll come back on for about 5 seconds and turn off for 10 repeating the process. After doing some research I thought it might be linked to bad auxiliary fans, I replaced them but they were still not coming on. I tested them by taking out the pig tail connectors off the red pressure switch and jumping the other ends. The fans came right on with the key in RUN.
Now here's where my problem gets worse. I decided to buy a new pressure switch and when I went to replace it. . . well, you guessed it, I lost all my freon. I had just recharged the system at a shop.

Anyway, all this was caused by me trying to fix the intermittent blower. (PS the blower motor is new also, and it's weird because it will blow all day on a not-so-hot day. It's just on the very hot days when I actually need the A/C that it does this cycle).

So two questions. Now that my system is empty I'm considering converting it to the cheaper r134a myself. What would that process entail?

And more importantly, what will fix this dang blower motor problem!? I've now traded out the blower motor, the auxiliary fans and the accursed pressure switch. What else could be causing this?

Cut a 1 centimeter square piece of paper and hold it up to the small grille near the rear view mirror with the key on. It should be held in place by the suction there. If not, find and check the sample blower. It is often to the right of the glove box but is in other places on some models in the 124 series.