GL 450 AC Issue
Thread Starter
Member
Joined: Aug 2019
Posts: 173
Likes: 36
2014 GL550; 2010 GL450
GL 450 AC Issue
I'm trying to fix an AC problem that came with a GL I bought – it blows outside ambient air with the following symptoms:
Is there anything else to check?
There was a Dew Point Sensor error code when I first scanned it but it hasn’t returned since I erased it. Live data shows Dew Point Sensor thinks dew point and ambient temperatures are 87.5 degC and relative humidity is 127.5%. which obviously can’t be right.
Would dew point sensor error prevent AC compressor from turning on even when commanded ON with diag tool?
Does anyone have factory service instruction for dew point sensor checking/removal/installation?
Any other suggestions?
- Static pressure for both high and low side is equal (between 70 – 100 degF) whether AC is on or no
- When I command AC compressor on with diag tool, it the hig/low pressure remain equal as above
- I check voltage at AC compressor connector and it’s 12V when commanded ON as expected
Is there anything else to check?
There was a Dew Point Sensor error code when I first scanned it but it hasn’t returned since I erased it. Live data shows Dew Point Sensor thinks dew point and ambient temperatures are 87.5 degC and relative humidity is 127.5%. which obviously can’t be right.
Would dew point sensor error prevent AC compressor from turning on even when commanded ON with diag tool?
Does anyone have factory service instruction for dew point sensor checking/removal/installation?
Any other suggestions?
Thread Starter
Member
Joined: Aug 2019
Posts: 173
Likes: 36
2014 GL550; 2010 GL450
Compressor has already been replaced as noted in "..Based on the above I concluded the compressor is bad so I replaced it together with new drier and expansion valve and filled with appropriate amount of R134a and oil."
Thread Starter
Member
Joined: Aug 2019
Posts: 173
Likes: 36
2014 GL550; 2010 GL450
Junior Member
Joined: Jan 2019
Posts: 22
Likes: 3
2012 GL450
Did the new compressor come with a new clutch or did you re-use the old one? If you used the old one, have you been able to verify that the compressor clutch is actually working? In other words, even if it is getting 12V, the clutch could still be not working if it is burned out.
Junior Member
Joined: May 2011
Posts: 32
Likes: 4
From: Las Vegas
2008 GL450
Essentially having this same issue. 08 GL450. Bearings in the clutch/pulley imploded and shot off the compressor. Serpentine nuked the idler before it shredded itself all over the engine bay. Rather than spend all the labor replacing just the clutch and idler to find out later there was compressor damage I just replaced the whole thing and accumulator. Vacuumed to -25 and added an oz of PAG then precharged high side. Attempting to charge low side it only takes 1 can and both sides read +75 on my manifold. No fault codes but I don't have a Xentry or MBII just a mid range Ancel so I can't use it to force a compressor engage. Looks like I'm climbing back under there with a multimeter to see if it's getting a signal. Worried that with parts flying around something else may have been damaged that I can't see. 
Rough part is it's been 110 every day here in LV so I gotta limit my time tinkering with it outside. Vehicle is useless when even a system 255 doesn't do much at these temperatures.
Rough part is it's been 110 every day here in LV so I gotta limit my time tinkering with it outside. Vehicle is useless when even a system 255 doesn't do much at these temperatures.
Last edited by Zodwraith; Aug 23, 2019 at 03:36 PM.
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Junior Member
Joined: May 2011
Posts: 32
Likes: 4
From: Las Vegas
2008 GL450
Of course, but I've had horrible luck in this town finding honest mechanics. The 2 nearby MB dealerships are total thieves. I'm not paying $2800 for a compressor replacement, especially when I walked out on my own job a couple weeks ago when I discovered how crooked my boss was becoming. 3/4 of us left the company. 😬 Hard to use the GL on the job search with no AC and it's been over 110 for over a week.
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Junior Member
Joined: May 2011
Posts: 32
Likes: 4
From: Las Vegas
2008 GL450
Well, good and bad news. Got under there this morning and wrestled that connector off and sure enough I'm getting 12.4v at the compressor so it's not computer/fuse/relay. I either have a brand new DOA compressor I fought 4 hours to replace or it's liquid locked from the PAG I put in. What's the easiest way to flush it before going all the way back to step one?
Edit:
SOLVED. It was simply a bent pin in the tiny connector preventing contact. Day and a half of checking and rechecking fuses, pressures, vacuumed twice.....all for a connector with a bent pin way down inside. Sigh... Working great now though. Wouldn't hurt to check yours Tadi when your symptoms are identical to mine.
Edit:
SOLVED. It was simply a bent pin in the tiny connector preventing contact. Day and a half of checking and rechecking fuses, pressures, vacuumed twice.....all for a connector with a bent pin way down inside. Sigh... Working great now though. Wouldn't hurt to check yours Tadi when your symptoms are identical to mine.
Last edited by Zodwraith; Aug 25, 2019 at 02:22 AM.
Junior Member
Joined: May 2011
Posts: 32
Likes: 4
From: Las Vegas
2008 GL450
Generally yeah but they all come "prefilled" and I didn't open and pour it to see just how much was in there, just added an oz or 2 to be sure. Evacuating takes mostly refrigerant not the pag oil. I was at my wit's end at that point wishing I'd checked the oil level before installing it in case it was overfilled from the manufacturer and I added even more. As you'll see from my edit above it turned out to simply be a bent pin inside the new compressor's connector. I only noticed because I was trying to get an alligator clip on it to run 12v directly and see if I could hear that little blip of the clutch engaging with everything turned off. I knew I had installed it correctly. 😋 She's nice and cool now.
Last edited by Zodwraith; Aug 25, 2019 at 03:00 AM. Reason: Spelling
Super Member
Joined: Apr 2004
Posts: 625
Likes: 82
From: Germantown, MD
'07 GL450
I came across this youtube clip which may, or may not, be related to A/C issues. The video makes a brief reference to cooling fan issues (may affect A/C performance) stemming from a bad SAM module. Posting here for any future value.
