hotbeer

Hi members ,my ac unit started blowing hot air through the right vent and cold air through the left vent. yesterday it started blowing hot air through all the vents and this is extremely unbearable. I took it to an ac repair company and they said it is cause by a faulty evaporater sensor and will cost $ 700-800.Do you think this diagnosis could be correct and the repair cost is reasonable ? This is a 2003 e240 m b

otto6457

Sounds reasonable but there are some simple tests to confirm it. Do you have a wiring diagram and know how to read it?

hotbeer

thanks for responding so quickly Otto6457. I dont have a wiring diagram but I was told that the entire dash board has to be completely romoved to replace this sensor and also that the system will have to be recharged.

otto6457

Removing the dash is really not that major. I find it amusing when shops make such a brouhaha over the fact that a dash must be removed. It's usually the independents that complain the loudest about dash work because most technicians have a natural aversion to interior work.

I'm not at work tonight so I can't look up the parts and labor costs, but $700.00 sounds reasonable for parts and labor if the evap temp sensor is bad. I have my doubts about the diagnosis but I'm in no position to tell you it's wrong. My reservation is that an evaporator temp sensor is a simple solid state thermister that seldom fails. Usual failures are damage from incorrect voltage application during a poor diagnosis, or physical damage. Not saying they never fail, but it is unusual. Your description sounds more like low refrigerant in the system. It's not uncommon for a system to lose refrigerant which causes uneven cooling of the evaporator assy. Which in turn can cause different temperature air to come out of different vents. Also, an evaporator temp sensor failure tends to display itself as normal cooling when the system is first turned on. Then the air temp gradually rises and airflow from the vents decreases. This occurs as the system won't control the temperature of the evaporator, allowing the temp of the evaporator coils to drop below freezing. This allows the condensation on the coils to freeze, which causes the air flow to slow down and finally, being restricted by the freezing so much that the air feels warm with little volume. Again, I'm not saying that the evap temp sensor is 'not' bad. I'm saying the symptoms don't make me think of the temp sensor first.

I will add that the shop simply evacuating and recharging the system might have solved your problem. Selling you an evap sensor which would require an evacuation and recharge anyway tends to hide a less than professional diagnosis. A voltage test along with a pressure test would prove the diagnosis.

If you trust the repair facility then you should take it in since the price quoted for the evaporator temp sensor (parts and labor) seems reasonable. (depending on the shop's labor rate and flat rate for the job) If you have doubts, get a second opinion from another shop.

Good luck

hotbeer

Thanks again Otto6457, your explanation is quite logical and I am definately going to seek a second opinion. I will let you know the result when it is corrected

Plutoe

I think that you do not understand your AC system and getting ripped off.

To replace the evaporator sensor takes at best one hour and fifteen minutes of labor with most of the time spent removing\replacing the cover below the IC.

Secondly the evaporator sensor does not control anything it reports the temperature of the cold air and shuts the compressor off if temps get to 2C to prevent icing.

Third your AC guy does not understand the MB system----get a second opinion and be careful

hotbeer

thanks Plutoe, you said removing/replacing the cover below the ic.Where is that located or are you refering to the ac control unit in the dash?

Plutoe

no, no look at the post I said IC not AC, for some basics IC=instrument cluster, AC=air conditioning, I can't believe this!!.

In any event move the drivers seat all to the rear, now kneel down place your back on the rocker panel and slide your body into the car, as your head passes the steering wheel look up you should see the----- cover below the instrument cluster, looking up locate all the fasteners they must be removed and the cover lowered to locate the evaporator sensor which is on the left side under the AC control use a flashlight and you will see the wire and sensor.

Please make sure someone reputable has tested the sensor before you put yourself through all these contortions and wasted time.