A/C blowing hot air and button flashing

SILVERADOCOACH

MEMBER
2006 MERCEDES BENZ SL500
5.0L
V8
2WD
AUTOMATIC
78,000 MILES

While driving cross country, came across an intense rainstorm and pulled over in a rest area. Took a nap and woke up to a non functional A/C system, meaning it was blowing hot air with the A/C button flashing. All my research to this point indicates a bad EVAP core sensor as being a common problem.

Without a computer analyzer, how to confirm the issue without just throwing parts at it?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi and thanks for using 2CarPros.com.

If the light is flashing, the best thing to do is to have the computer scanned for trouble codes. I noticed you mentioned that you do not have an analyzer, but that is the only way to be sure where the problem is coming from.

In this case, you cannot just use a generic type scanner, but rather one that can read all the different types of codes, including the ones for the HVAC. Honestly, it could be many things, including low Freon or a bad pressure sensor. For you to replace the sensor yourself, you will have to evacuate the system replace the part, then recharge the system. Keep in mind, the only way to determine if the sensor is bad is with an analyzer. Checking the system with pressure gauges may indicate it is normal. However, what that sensor tells the computer could be different.

I realize this most likely is not what you wanted to hear, but I am trying to help you from throwing money at it for no reason. If you have manifold gauges, you could check the pressure in the system. That would at least tell you if it is something as simple as low Freon. Here is a link which discusses how to evacuate and recharge using gauges. If you let me know what the temperatures are where you are located, I can tell you what pressures you should have.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Let me know.

Joe