SL65AMG_KUN

Hello my friends,

I own a 2006 Mercedes Benz SL65 AMG

Recently I replaced the spark plugs and ignition coil packs, then the AC started blowing hot air, I tried to reset the AC system but I couldn't, I replaced the evaporator sensor but it did not help, I did the 3 seconds reset as well it didn't help.
I took the car today to Firestone, they diagnosed the system and advised me everything seems fine but the car is not sending a signal to the compressor to start and told me to take it to the dealership.
I am hoping a reset of the AC system would fix the issue,
anyone can help me with that matter please, and if you have any idea how to get the AC to started.

Thanks

cdk4219

First off Firestone isn’t the place to take a car like that for air conditioning diagnosis, or any other repair besides possibly tires for that matter . You really need a decent diagnostic tool for these things. It could be any number of things, but guessing without a proper tool like icarsoft, foxwell or the xentry is really wasting time.

g0rsq

I agree. You need to get it on Mercedes specific diagnostics.

The compressor is running all the time, so there is no "Start signal".

The compressor is controlled from 0% to 100% by a Pulse Width Modulated signal from the front SAM, so you need diagnostics (or electronics know how) to measure this, and read back what the compressor is doing.

Greg Elmassian

I have the icarsoft unit... the HVAC reports pressure low, the ECU reports the pressure high..... weird... when I clear the errors, they come right back... I guess the next thing is to check actual pressures and see who is lying?

Aussiesuede

When the HVAC senses low refrigerant it automatically shuts down the AC. The AC will not work again until the system is first refilled and then the system must be reset. So if you are resetting the system and it is immediately disarming again, the most likely culprit is low refrigerant. There is nothing special about adding refrigerant. Just attach the connector from the can to the fill port and refill until the dial shows in the good range. Then reset the HVAC with your ICarsoft. Simple as that.

Greg Elmassian

got that, was looking for comment/experience on HVAC reporting low, and ECU reporting high... maybe the ECU is reporting high ambient, I also notice 185 degrees outside so better fix the ambient sensor first...

Abebundance

Did you have any codes when you were scanning the system?

Greg Elmassian

Yep, will post them, but my brand new aux battery died just yesterday, gotta go get a warranty replacement... will report back, any help appreciated

Greg

aegea

I replaced my new auxiliary battery when an aftermarket alarm was going off silently, and drained the battery a few times. I saw various low voltage codes, maybe even for the A/C. i HAVE CLEARED THE CODES SEVERAL TIMES UNTIL THE A/C magically started working again. These are DTCs, not just OBD2 codes. You need more than an OBD2 scanner to clear DTCs. I use an Autel Diaglink or DAS.

Greg Elmassian

OK, some headway with a new battery fitted.
I was fixating on why the ECU says the AC pressure too high, and the AC system says pressure too low. (I'm going to buy the gauges this weekend)

I saw some faults in the multisensor... the CO sensor says the value is 1023 (which is a suspicious number) and also that the humidity is 128%

That combined with the ambient air display showing 185 degrees, means at least some sensors are nuts.

So, I think on a 2003 SL that was made in 2002, the ambient temp sensor is in the center under the front air dam? Anyone confirm or have picture of where?

Don't know about the other sensors. Is the multi-function sensor a single box/device?

Will get true refrigerant readings this weekend.

Again thanks for all help and suggestions.

Greg

Greg Elmassian

Pulling codes, the AC system says current and historic refrigerant pressure too low. Bought a set of gauges, and no, I do not have low refrigerant, low side is 35-40 psi in shirt sleeve weather. The high side is low of course, since it is not pumping fluid...

That's 2 of the DTC codes, B1257-000 and B1257-001 - pressure too low, but the low side is fine.

There's a 3rd DTC, B1269-000 which is communication failure with the ACC Multifunction module.

The multifunction module reads CO: 1023, Nox: 1023, dewpoint no data... Also I'm still showing 185 degrees ambient on the dashboard, after replacing the ambient temp sensor in the grill

So going after the MF sensor module, in a cover/box, found it just behind the starter battery positive terminal, in a little box attached to the vents in the hood...

Help needed: how the heck do you get this box/cover off so you can remove the module?

Update, got it off, so now I guess replace the unit...

I still have a relay that clicks like crazy when the car is on, which is circuit 15R.... but does not seem to control anything I have... any clues on 15R?

Anyway, off to buy a used module

g0rsq

circuit 15R is a significant circuit, so no idea why it clicks. It feeds all fuses marked Terminal 15R. What relay is actually clicking

Greg Elmassian

The relay that turns on the power to 15R, US car, so left fuse panel in the engine bay,

Relay C

https://benzbits.com/R230/Fuses/Left...gineRelays.pdf

It's clicking rapidly, I have not debugged it yet, perhaps not quite enough current to keep it held? Seems strange.

Been trying to debug the AC first.... waiting on a multi-sensor unit, since the temp on the dash still says 185.

Any help or suggestions appreciated.