AC/Heat won't turn off
 

moved to NYC a month ago, came home, and started to drive my car. When I was driving i noticed the heat wasn't working so I hit the reset button and it started to work. I thought everything was fine, but when I turned to knob to make it go off it didn't (it works on all settings and changes strength).

Now, when I got home and turned off the car completely it keeps running and won't turn off at all. I have let the car sit for 20 minutes and it is still running. any ideas on why this is happening and how to stop it?

Re: AC/Heat won't turn off
 

Re: AC/Heat won't turn off
 

meant rest button sorry.

have hit it multiple times and it still won't turn off. have tried with the car on, off, etc.

Re: AC/Heat won't turn off
 

Try pulling fuses 15 & 36 in the under hood accessories box.
If that makes the fan stop and the light goes out, then you most likely have a hosed A/C Heater control module.

( try 04 05 06 07 Crossfire Temperature Climate Control 1714789 | eBay )

Re: AC/Heat won't turn off
 

You have a problem that is actually common with our cars. I have owned my car eight years now and bought it new. I had a similar problem twice. In my case the ac was off but it would turn on and off on its own. Now matter what speed setting I pick it always blew at the same speed. Not sure if it is a relay or the actual switch unit in the car. I had it replaced under warranty twice and never paid attention to the dealership explanation. I think it is an 800 dollar part though which I am sure you could get cheaper directly from Mercedes.

Re: AC/Heat won't turn off
 

Sorry, I just read your post again, so just scroll down to the section about the Blend Door. The first section are the first steps to testing your AC, still good information.
If the problem is your system (fan blower) won't turn off then yes, then read the pdf the gentleman wrote about fixing his blower working intermittently.
The thesis I wrote below is still good information.

If anyone is planning on working on their AC system, shoot me a note. I can help guide you through the process and provide very helpful tips.

I just did a complete overhaul of my AC system- I flushed the evaporator, no way I'm getting into that mess.
So, you say the system was working intermittently then nothing? Correct? When it comes to the AC, there is only one place to start...

1. Is the clutch engaging and spinning when you turn the system on?
2. You said you had the freon checked and it was good.

If it ran intermittently then died and the clutch is not engaging, then how did the mechanic know the freon level (pressures) were okay?

• Did he perform a static equalized pressure test?
• If the clutch won't engage and the high/low side pressures are good (and they equalize), then the most likely cause is either the compressor clutch gave up the ghost, or the high-pressure switch on the accumulator went bad.

To check the pressure switch, you'll need an ammeter. That funny looking calculator with the sharp pointed wires and a big knob in the center.
WARNING: Do not attempt to remove the switch from the accumulator. These cars do not have Schrader valves in them and all your freon and some oil will come blowing out.

1. Set the ammeter to continuity. Watch YouTube if you need instructions.
2. Set the ammeter switch to continuity or Ohms.
3. The high-pressure switch cycles your compressor clutch. When the pressures are good the switch closes and transfers approximately 5V to the compressor and the clutch kicks on.
4. Remove the connector from the switch and in the back of the switch will be 3 connectors. One will be power, another ground, and usually the middle one will be the signal to the controls.
5. Alternate touching your ammeter probes to all the different combinations between those three prongs. If at any point, when you touch two you hear the constant beep of the meter, your switch is good.
6. If not, start the car and turn the AC on, SET YOUR METER TO LOWEST Voltage setting and alternate between the connectors. If the meter reads 3-5 volts, then you're getting power up to the switch and your problem is the switch.
7. To test the switch, tape two AA batteries pos to neg, this will make 3-3.5 volts. Tape a length of thin wire, stereo wire will work to both ends of the batteries, so you have a positive and a negative wire.
8. Now, like you did with your test probes, alternate between the three prongs on the switch. If the compressor kicks on, your switch is good, if not, it's probably your high-pressure switch.

If the clutch does engage, then I'd look at the "Blend Door" actuator. These cars are notorious for these actuators going dead, why? Because everything runs off of vacuum.
Go on YouTube if you need to know how a blend door works.

To troubleshoot the Blend Door, first start simple- You need to access the engine side of the firewall.

1. Remove your battery
2. Remove the battery support underneath
3. Look at the firewall for a grey or whitish tube coming out. It will be a thin tube about 3/16"
4. We want to check for any kinks or openings in this tube, so follow it under the ECM box and along the firewall.
5. All Good? Now remove the intake cover (air filter box)
6. That tube will continue to the back of the engine manifold where it slides in to about a 1/8" piece of rubber vacuum hose.
7. That vacuum hose is responsible for more than half of the AC problems out there.
8. That rubber vacuum hose connects into the back of the intake manifold where it uses vacuum from the intake to operate the blend door.
9. Don't be afraid to pull this rubber hose off and inspect it. The grey tube slides into it and it slides onto a ni pp le on the manifold.
10. If this hose or any part of the grey tubing is bad, replace it with a length of the same sized rubber hose on the back of the manifold.

Once you've done these things, let us know and we can guide you or praise you.

Re: AC/Heat won't turn off
 

This is a 12 year old thread

Re: AC/Heat won't turn off
 

Thanks, Valk. For some reason I got the impression, well it doesn't matter. Maybe it will still be useful to someone.
Cheers!