W124 300D air conditioner not cold during idle? - PeachParts Mercedes-Benz Forum

NickMendoza · #1 07-17-2004, 03:19 AM

On freeway AC gets so cold that I have to turn it down.

ON the street = AC semi works...I put my hand to vents to feel a little cold coming out.

Have a new receiver dryer.

System Flush - R12 - no leaks

Is this normal? Please help.....

Thank you

Nick Mendoza

stevebfl · #2 07-17-2004, 01:46 PM

The difference is normal, the amount of difference may not be. Early 124 cars had small compressors that were never great.

If your system is working properly refrigeration wise I would look to a recirc door sticking open. In the AC position the recirc door is always closed on the first stage to 70% closed. If it doesn't it will mean a 10-15 deg duct temp change.

Chevota · #3 07-17-2004, 04:38 PM

I'm assuming you have good air flow coming out the vents in the dash? If so, it sounds like your AC is working normally, but you aren't getting airflow thru the condensor at idle. The condensor looks like a thin radiator that's usually placed in front of the engine radiator. There needs to be good airflow thru that condensor to dissipate heat just like the engine radiator needs it. Basically, the AC system takes heat from the cabin of the car and dumps it off at the condensor. If there is no airflow thru the condensor to carry that heat away, then it just goes right back into the cabin. So if there is little or no air being drawn thru there, you will need to find out why. If that's the case let us know.

If you simply have very little airflow out the vents in the dash, then you need a new blower motor. (At higher speeds air will be forced into the car thru the vents)

LEADFOOT · #4 08-27-2004, 09:32 AM

Nick-

How did you make out? I have the same situation, almost. I have a '92 300E.

When I'm on the highway at higher rpm's I stay nice and cool. Soon as I hit the brakes or slow down to 1500 rpm air gets warm (balmy warm). I had no air out of the in the center 2 vents. They are now open fully. My mechanic replaced one of the vac pods.

I read Steve Brothertons article (June 2000) in the DIY section and it mentions the compressor control relay system (Klima). I thought of this as a possible culprit. In my case, I don't think that is it.

idle is 600-700rpm (per inst. cluster)
checked the voltage. Charging is good (14v)
Flushed, checked - no leaks found (dye)
R-134 conversion by previous owner, originally R-12 (stamped)

My main cause for concern is the window get fogged at a traffic light during rain or going thru carwash. Seems like the recir is the culprit with me if humidity is getting into the car. Is that what solved your problem?

(Steve:If that is the problem, Can I fix this myself? ie. without pulling the dash?)

thanks,
Preston Worsham

psfred · #5 08-27-2004, 09:59 PM

Make sure the aux fan is running when the AC is on and the engine warm -- most importantly, check the fuses! They are all corroded by now, and i discovered that my aux fan fuses were bad. If so, you won't get good cooling at idle because the head pressure is too high.

I would also test all the vac servos, especially the recirc servos. If they aren't giving you recirc, or the flap isn't closing all the way, you will get warm.

Also, pull the glove box and check the sampler motor and hose -- make sure the hose is actually attached to the motor, it gets hard and slips off. A small slip of paper about 1 cm square must stay up on the little grille next to the dome lamp, too. The interior temp sensor is behind there, and if the little blower motor isn't working, the temperature control will be erratic. You should not freeze on the highway and roast while sitting.

that said, it will be warmer at idle than at 1500 rpm due to the limits of design -- if the compressor was big enough to keep you cold at idle, it would explode or freeze you to death on the highway!

Peter

NickMendoza · #6 08-28-2004, 06:39 AM

Yes, I found out that the design was the problem.

When I am on the freeway the air is so cold that I need to turn it down.

When I am on the streets = the air does get warmer.

This is the design. I have to live with it. That is ok.

Does anyone know a larger unit that may fit without a lot of problems?

Thank you

Nick Mendoza

LEADFOOT · #7 08-28-2004, 11:37 AM

Thanks Peter I enjoy reading you posts.

I have a quick question. Could the fuses (rather than vac lines, etc) contribute to the warm air at low idle problem? How so? I believe in trying the simplest solution first. That said, the fusebox is where I am starting.

The car I have is a Calf. model, also, was originally R-12, converted to R-134. I was told that in cars designed for R-12, a conversion will adveresely affect ac funtioning because the evaporator and condeser are smaller than in R134 systems. I would think that the R-12 system would perform superior and converting to R-134 would be part of the problem, or a potential problem. Is this correct?

thanks again,
Preston

#8 08-29-2004, 09:57 AM

NickMendoza,

You have concluded that the design is the problem. Does that mean that you have checked your vacuum pods, your sampler blower and your aux fan and have found all of these subsystems functioning properly?

You have been given some very good advice in this thread. I would have expected that one of these suggestions would have uncovered a malfunction that is leading to your problem.

These cars do indeed have a marginal a/c system, but if everything is working properly it will not perform as badly as you describe.

LEADFOOT,

A bad fuse on the auxilliary fan is what I believe that psfred was referring to. The aux fan adds air flow across the condensor at idle, thus when it is not working, the decreased air flow will decrease cooling effect in the cabin.

Checking fuses is not the ONLY simple test you can do. Testing the vac pods is very simple, just pull the glovebox and apply about 3.5 in HG of vacuum to each of the seven lines on the manifold at the lower left of the glove box opening. Using a 1 cm piece of paper on the sample grill is very simple and checking all your fuses is very simple.

Good luck to all,

LEADFOOT · #9 08-30-2004, 05:23 PM

Larry, thanks for your response.

The auxillary fan is operable, but not as expected. I cold started and they came on even though the a/c was switched off.

I turn the car on, turn on the a/c switch and the aux fans do NOT come on.

Should I replace the relay? there appear to be two. a preresistor and an aux fan relay in the B and C positions.

I performed a vac check w/ the 1 cm piece of paper. It appears as though the lines are all working.

Many thanks to all.

PW