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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53017
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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This is e420 4matic. When i start the car with ac on cold it

Customer Question

This is for 2004 e420 4matic. When i start the car with ac on cold it doesnt blow cold air this is automatic mode. As soon as I start pushing buttons which control from which vent air is coming ac is working properly and cooling the air as expecyed
JA: Does the engine turn over? How old is the battery?
Customer: Engine is starting fine, no indication of weak battery this is happening when engine is running
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: So far taking ac out of default mode bu "telling" the car which vent should air come from is getting me cold air
JA: Anything else you think the mechanic should know?
Customer: I try to purchase this vechicle so my knowledge of the car is limited but looks like it is in great shape beside this semi-operating ac
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and then connect you two.
Submitted: 3 months ago.
Category: Mercedes
Expert:  Marty replied 3 months ago.

Hi, welcome to Just Answer. My name is***** sounds like a fault with the actuators for the mode doors in the dash. Everything is controlled electronically. You should get the car connected to the Mercedes Star Diagnosis tester to have a diagnostic test performed on the actuators. Any faulty or sticking actuators will store a fault code in the computer. Replacing the actuators can be expensive so I suggest that you have the car checked before you purchase it. It is a good idea to have the entire vehicle inspected by a Mercedes technician prior to making your decision.

Let me know if you have any questions.


Customer: replied 3 months ago.
But doors in the system are opening and closing properly as air is coming from right place. It is just that initially car blows hot with AC default settingWhen I play with module (butons with circle arrow on AC unit) and set up for front blow or any other position (this is moment when indicator light lit and show which vent supply air into cabin) that I start getting cold air and after that all is working fine. I got cold air and air is directed where I want.Sounds like I have to "wake up" the AC from default mode and then all is working properly.
Customer: replied 3 months ago.
Definately want to take car for inspection but not willing to spend 300 for discovering issue and not purchase the car
Customer: replied 3 months ago.
If that will be issue with acutator I will expect to get cold or hot air from the apecific vent all the time right? This is not the case as soon as I play with ac for a second right air is coming from right vents and AC operates properly
Expert:  Marty replied 3 months ago.

Hi, aside from the actuators the only other possibilities are the control unit itself or one of the sensors in the system or low refrigerant in the system. During a normal pre-purchase inspection the technician should connect the Mercedes tester and scan every module in the vehicle for fault codes. The codes will tell the technician where the problem lies. At this point he will have a fairly good idea as to the problem. I normally advise my customer's to negotiate the repair into the purchase price of the car or have the seller repair the problem before you buy it.

Let me know if you need anything else.


Customer: replied 3 months ago.
Will low coolant create such issue? I will expect with low coolant air will be always same temperature.In addition can you help me with other questions I have for 2001 e320 (actually also AC related)
Expert:  Marty replied 3 months ago.

Low refrigerant could cause the compressor not to turn on immediately. I'm wondering if the air would eventually turn on all by itself if you didn't touch anything. If it won't then I would say that the problem is with the climate control or the actuators. The fault codes stored in the climate control will point to the problem.

Yes I can help you with the E320 but you are supposed to open a new question for different vehicles. If you want to rate my service on this question and start a new one on the E320 I will be glad to help you. Just be sure that you request me when you open the question.

Customer: replied 3 months ago.
Good point on trying not to touch anything. I actually drove the car for about 5 min and it was still blowing hot. Coudnt take it any more hot air on hot day so I gave up and started playing with controls and get cold AC going. Good thing is air is coming from right places (this is actually issue with my 2001 as I lost this ability there but I wont bother you this as I understand I should start new tread).One more question on 2004 e320. Beside AC issue I noticed quiet whining noice (similar to speedo cable noise on older motorcycles) when I reach about 5000rpms during fast acceleration. Any ideas on this one? No noise when car is at lower rpms all nice and quiet. Woudnt even probably hear this if AC or radio will operate but I was listening when every noise source was eliminated during the drive
Expert:  Marty replied 3 months ago.

I've seen a bad compressor act that way.

In regards ***** ***** whining I would suspect a noise from the differential. When the differential gets noisy it makes a whining sound. It usually goes away when you back off the throttle. Tires can make a whining noise also but it's usually all the time.

Customer: replied 3 months ago.
As far as diferential noice should I expect this noise to last during highway speeds all the time. Noise is definatly related to rpms not as much to speed of vehicle as as soon as trans shifts to lower rpms it is nice and quiet
Expert:  Marty replied 3 months ago.

Okay, then it's definitely not the differential. Possibly a transmission fluid whine. A fluid and filter change might help. Power steering can whine like that also.

Customer: replied 3 months ago.
Rather not power stering as I got this issue on my 1994 e420 and it was noisy during turning - sounds more like mechanical noise but I doubt these 2004 still have cable in speedo. Here I hear it when accelerating straight. Will such noise only be present during high rpms and could be because low fluid level?
Expert:  Marty replied 3 months ago.

Normally you would associate a power steering noise with turning the wheel. Without the benefit of hearing the noise it is hard to say what it is. I'm inclined to think it a transmission whine or a whine from one of the belt driven components.

Customer: replied 3 months ago.
I just talked to local MB technician who mention that since AC issue is semi working it might be also related to preference of driver that key is remembering. Here based on key used car will set up latest driver preference and activate AC based on this. Are you familiar with this? I was also wondering if after I "play" with AC I can go back to default set up (no light on vent indicator on) which will allow me to check if issue continue. I think car is P2 package which maight have this option bit not sure.As far as whining sound looks like this is consistent low fluid or trans flush was recommended.Let me know what you think
Expert:  Marty replied 3 months ago.

The key preference is overridden as soon as you press a button on the climate control unit. That won't be the problem here.

On the transmission I prefer replacing the filter and fluid over flushing the transmission.

Customer: replied 3 months ago.
If AC will be overwritten by touching AC unit that will be really consistent with what I experienced. Can I go to default set up after playing with settings meaning (no light on right control on)?Where I can figure out if this specific car has this option? Or how is this option called (if anything)
Expert:  Marty replied 3 months ago.

It would not be consistent because you have to play with the buttons. For example, if the climate control comes on and is set at 65° cooling it should cool at 65° as soon as you press the Auto button.

Customer: replied 3 months ago.
that is correct. Can I go back to default after I change settings initially? Can I check if car has key that AC memory settings? If yes how
Expert:  Marty replied 3 months ago.

A 2004 did not have key memory for the climate control. This car simply remembers the previous settings of the seats and climate control.

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