S Naqvi

2017 GLS 450 96k.

The AC stopped working all of a sudden took it to a couple of shops the refrigerant is perfect and the compressor does kick in but the car constantly blows hot air. All events below the same amount of temperature so I'm wondering if it's not the freon not the compressor how do I check to see if the control unit is operating? All the buttons are lighting up as they should be the defrost kicks in and the vents blow up against the windshield the max button initiates the blower at full speed but no cool air. Has anyone experienced this issue?

John CC

Find where the AC lines go through the firewall or into the ventilation system and see if they are getting cold. If they are, the problem is in the control or the motors that operate the vent dampers. If not then it's related to the refrigeration system. Did the shop that blessed the refrigerant as "perfect" check the operating pressures? If they are "perfect" too then it's likely you're getting air from (only) the heater instead. Did you try setting everything to maximum cool?

S Naqvi

That's genius... but which line is that?

John CC

That one should be cool if not cold when the AC is running. It says "Suction" which men it's the return line from the evaporator (cold) to the compressor. It also has the low pressure test fitting on it.

S Naqvi

OK then that line is warm when AC is running.

John CC

You need to know what the pressures are.

S Naqvi

Ill ask. So if its low what does that mean? And if it's high what would that mean?

thanks

John CC

It's complicated. There are two pressures, "low side" and "high side". They are both important. here's an over simplification:

If both are low it's under charged. If both high it's over charged. Too close to each other and the compressor is probably weak. Too far apart and there's a blockage.

S Naqvi

This is really helpful. Does the 2017 GLS have issues with the line collapsing?

John CC

What line collapsing? Lines under pressure rarely collapse.

DaveT.D.

Related question. I also have a 2017 GLS 550. Purchased used 3 years ago. Entire time I've owned the vehicle, upon startup the A/C blows hot for 3-4 minutes, and then cold and cools the car fine. Is this normal? How long do others experience before the A/C blows cold? If not normal, things to check?

Thanks, Dave.

John CC

Sounds similar to ours. Maybe not 4 minutes, but at least 2. Seems longer than usual. My guess is there's a temp sensor on the evaporator and it doesn't route air through there until it's "cold enough".

FWP!

Have you had freon levels checked? Sounds like it's low.

S Naqvi

So, I finally took it to the dealership. They are telling me the compressor has to be replaced. I haven't gotten a quote yet but any ideas what repair range should be for this?

Diamond Dave

Why people take 10yr old European cars to the dealership and pay their incredible prices is beyond me. A dealership wants to fix problems by replacing all the old parts with new parts. An independent shop wants to diagnose and resolve problems so they don’t have frustrated customers.

Dealership - $3500
Independent shop - $1800
DIY - $600 + AC recharge

S Naqvi

If the compressor is busted, would you also change the dryer too?

John CC

It's never a bad idea to change the dryer any time the system is opened. If the system has been opened or out of Freon for any length of time then replacing it is a must.

S Naqvi

15​​​​00 for compressor and with drier its 2200.

John CC

I can't think of a reason it would be more than $200 extra. The part is about $165. (Compressor is around $1000 for the part.)

Try somewhere other than the dealer!

thtguy

you can get a full kit with a Remanned compressor, dryer, all the o-rings and new expansion valve for less than $300 on Ebay. replace everything yourself, drive it to an A/C shop tell them it is all new with no oil, have them vacuum it down, add oil and refrigerant... and you are golden!

or from FCP new Genuine Mercedes Compressor just under $1k, expansion valve is $61, and I can't find a drier on FCP so you will have source that elsewhere.