Hello everyone,

I have a 2010 GL 450 with 105k miles on it. I am pretty sure the HVAC system in it is all original. I have been running into cooling issues. I can start the car and let it sit in the garage and the AC will seem to be cooling. but the vent temp is only blowing around 62 degrees and that is with the dials set to max cold. I can pop the hood and check the LOW pressure line with my hand and it is hardly cool at all. it should be cold and sweating condensation. BTW, I am in Texas and the outside temp is well into the 90's when I am testing this. As soon as I start driving the car, it just starts blowing warm air from all the vents.

I have read that it might be the Climate Control unit, so I started there and ordered a replacement CCU and installed it. That did not fix the issue. I also have an Autel 4 OBD2 system scanner and when I run a full system scan it does not show any HVAC error information. I was thinking that I might have a short in the compressor but I am not seeing anything.

I ordered a new compressor and dryer unit for it. I guess the next step it swapping out the compressor.

If anyone has any ideas on this I would greatly appreciate any feedback.

Thanks,
Chris

 

Have you tried adding freon?

 

Yes, I have but I dont have a set of professional gages to see the pressures. So I am guesstimating.. : ) I dont want to over charge it.

 

You can go to Walmart and get one that attaches to the can. It works good enough. It's probably just low on freon. Refill or have a shop pull a vacuum and refill. You can buy everything online and DIY. It's super easy. You need the vacuum pump, gauges, and cans of freon. Will still be less expensive than taking to a shop. If that does not work, then you can do the compressor but it is unlikely in need of a new one after 100k miles.

 

My 2007 GL450 has been in Houston all its life. Its AC died a slow death about 10 years into its life. Symptoms were less cooling on driver side first. In 2018 season It was helped by some addition of Freon. But low pressure line reading was high in 2019. I figured that compressor is not compressing enough to decrease the low line pressures. Finally few months ago, I replaced the compressor and it solved the issue completely.
The first step for you will be to check the low pressure lines with AC at full blast on and max settings. If the pressures are high (>35~40) in low side, it is probably your compressor dying. The build quality in OEM compressor is good, so it doesn't grenade but dies slowly (so I heard is starter motor in these trucks).
so you can start at following product.
https://www.walmart.com/ip/A-C-Pro-A...0-OZ/353326131

 

Hi Chris,
I've done a LOT of AC work on my cars over the years (Including swapping out every single part of some systems) and this can be a hairy and time consuming task -but- you can do it successfully.
I have all the empathy in the world for what you are about to undertake...

Thought #1: You need good measurement devices!!

Never shoot in the dark. As the previous poster stated, you do need a set of gauges to see what's happening on the hi and low sides. Then there are some deductions you can draw off of that info. (FYI-My local O'Reilly Automotive 'loans' these gauges out for a deposit. AutoZone may as well...)

You also need a good temp gauge. I don't mean expensive, just reliable and DIGITAL. Don't use an infrared gun that you point at the vent. Don't use the analog thermometers. Get something like a digital meat thermometer and stick it in the center vent on the driver side, leave it there. Always take your temp measurements in the same spot and with everything on the same settings. (Fan speed, temp, recirculate, windows open/closed, rpm etc)

I have been amazed at how 'picky' car AC systems are about the fill level. Slightly underfiled reduces cooling, and slightly overfilled reduces cooling.
Many people end up replacing major components because they 'add a can' of 134a and unintentionally take the car from underfilled to overfilled, so it still doesn't cool adequately and they assume the compressor or something else is bad.

Here's a pretty pain free, easy, & cheap way to approach this task:
1. Measure and record the current temperature coming out of your vent after the car has been running for a while and the temp has normalized. That is your starting point.
2. Check the system pressures while it's running to see if you have an issue such as a blockage, or overfill, etc. (ask if you have Q's about this)
3. If BOTH of the pressures are low (on the low -and- high side) then add A LITTLE refrigerant. I mean VERY LITTLE. Like 1/10th of one of the small 12oz refrigerant cans.
4. Let the system run for about 10min to equalize (I know that seems like forever) and then...
5. Recheck your digital meat thermometer that you have in the vent with everything on the same settings. Record the new temp. Is it improved? If so, keep adding in SMALL bursts until you record your lowest temperature.
On the other hand: If you add a small amount and the temp gets worse, you may be currently overfilled from adding the can you mentioned previously.

Here's why you should do this:
You're going to have to do it anyway! If you replace the compressor and dryer (and perhaps other things) when you refill the system with new refrigerant, and if you don't get the fill correct, then you will still not have a properly cooling system and you will spend all sorts of time and money chasing down other problems. Ask me how I know...

Not only is this something you will ultimately have to do if you replace components, it's the best way of avoiding replacing components that aren't the problem in the first place. (Like a CCU)
BTW-I hear HVAC guys refer to this as the Approach Method, and it's the best method I've used so far.

One final thought:
On these new computerized systems, there are many sensors and other things that can be causing a system to cool poorly.(ie Heat load sensors, Temp Control Amplifiers, etc) If the pressures seem normal, then your actual problem may be elsewhere. Dont jump to adding refrigerant. Otherwise the problem really gets compounded.

 

Thanks for the reply. I do have a feeling it is the comp going bad. it has done a few other strange things over the last few years. we were actually driving back from the woodlands a few summers ago, and it started blowing warm air. I pulled over at the next gas station to fill up with gas and after i restarted the car, it started working again. And it has done that about 2 time since and restarting the car always seemed to help. But now its just not working anymore.

I did just get my new compressor and dryer in today. So I will be setting some time aside to do that job.

 

justin3219

Thanks for all of the great detailed information. At this point, I am going to just replace the Comp/Dryer. Just got the new one in today. I will probably just go ahead and buy the gages and the vac pump to get the job done. I hate taking anything into the shop...

I will be referring to your instructions when i start this project. Thanks again for all the great information.

I will let you all know how it goes!

Chris

 

I borrowed the guages and vacuum pump from autozone to do my job. I am like you as well that I hate taking it into a shop. You don't have to buy guages as you can borrow them and you won't need them ever again.
You will have to check the pressures/vacuum anyway, so do check them before replacing the compressor to make sure there is no leak. Low Freon needs to be ruled out before we diagnose it as bad compressor.

If you do end up replacing the compressor, there is diode thread on this forum in case you get error 9006 if it is not Denso. I had bought one on ebay (https://www.ebay.com/itm/283743055760) and my luck was good that it worked good out of box.

https://mbworld.org/forums/gl-class-...ompressor.html

 

Yea, I bought some of those diodes to try out, but I am not getting any 9006 code when I run a scan on the car. Do you think I should try the diode trick before I do the swap?

Here is the new comp that i bought.

 

That diode trick is only useful if a NEWLY installed aftermarket (non-denso) compressor doesn't work or works intermittently. Since this doesn't apply to you currently, so no need for it yet. If your new GPD compressor doesn't work, then it will be a possibility.
OP of that thread did use a GPD compressor that needed the diode. (https://mbworld.org/forums/gl-class-...ml#post7751389)
This link might offer some education about that diode so that you can identify on your old compressor control valve.
https://www.denso-am.eu/media/132305...ac-2019-eu.pdf

 

Hi Chris,

I'm wishing you the best on this project but listen, the previous intermittent problems you mentioned really do *not* sound like a bad compressor to me...
I've experienced this exact situation on another car and in the end, it was a Temperature Control Amplifier. Which is small, cheap and easy to replace item.

Even logically, if you think about it, the AC compressor is a pump. Fundamentally similar to an air pump. There are several ways they could go bad, but really none of those failure modes involve intermittent operation. (That I can think of)

Those problems are more likely to be electronic in nature.

One thing to check before you go thru all this work and expense is this:
With the engine and AC running until it normalizes, does the compressor kick in and out? Or does it stay running 100% of the time?
If it kicks in and out, how long is the run time and the off time?

Here's why I ask:
If the compressor runs and never shuts off, then one explanation could be that the compressor is not pumping properly. (Maybe its pistons are worn/time to replace)
The other explanation could be that the refrigerant level is too low. (Gauges would show low on both sides Low/High. Thats why we check it first)

If its kicking in and out erratically, or staying off, then you can override the AC clutch and force the compressor to stay 'on' by using a jumper wire. If you force it to stay on (Compressing) and all of the sudden you start getting cold(er) air, then you can have more confidence that this is an electrical control problem. (And it would indicate that your compressor is good)

Just friendly advice! Your heading toward a path of high cost and effort. I'm hoping to help you dodge the bullet if its not totally necessary
Not only that, but if your problem is a sensor or circuit, then that problem will prevent your new compressor from performing correctly too.

Cheers & good luck!

 

Here's something free and easy to try:
Pull this evap temp sensor out, but leave it connected, and let it just hang in the warm cabin air. In other words, take it out so the evaporator isn't cooling it, and let your AC system run.
What happens to the temp of air coming out of the vents?

 

Its an electronic compressor, it does not have a clutch like most standard compressors so I cant tell if it is engaged or not. That is a frustrating feature.

Chris

 

I have the 2010 GL 450 X164. I dont think this will work on that car. At least from the description that you posted.

 

Check the freon level as stated earlier and by others. No need to put on a new compressor unless absolutely necessary.

 

From your description it sounds like it is low on refrigerant, evap leaks are very common on that chassis by this age. I'd ensure you have a properly charged system before you start throwing parts at it, save yourself the guesswork and wasted money.

Also, in my experience, the compressors don't "gradually" go bad. They work, until they seize up and fail. Now, if it's not cooling and then start to cool after some driving or a hard rev, it can be the refrigerant control valve sticking, which is why there isn't a clutch on the compressor, they are variable displacement. The valves usually stick in the "off" position, and then move back to working levels after a time or some hard rpms.

 

Okay, both of these are new bits of information for me. (No electric clutch and the variable displacement thing)
Fortunately I have not had to work on my GL's air conditioning yet...

Would be really handy to put a set of gauges on there to see what's happening first tho. As ItalianJoe1 said, a metering device such as the refrigerant control valve could be at fault.
On most cars, that problem would result in a high side too high -and- low side too low pressure situation.

Even if you did throw the new compressor on there, you would want to be using a gauge set to pull the vacuum and to correctly refill the system so maybe try to go ahead and do the loaner program and try testing your pressures before you pull off your current compressor.
Who knows, might save you a lot of time and money! (Hopefully)

 

Sorry about my oversight. I have a 2008.
I think the 2010 version may look like this below:

Same test method could benefit you if its easy to do. I'm not 100% sure where this is on our GL450's but if its handy, it can be a quick and easy test IF the refrigerant pressures look correct.
The ad states it's on the Evap.

 

Is the control valve in the compressor?

 

I believe what he is talking about is an expansion valve. (Sometimes called an Expansion Block) They are usually near the evaporator coil, so on most cars that is just inside the passenger compartment under the dash and often down by the passengers feet. Some cars have it just on the engine side of the firewall but inside some black AC housing, and also usually on the passenger side.

A small piece of debris can cause them to get stuck and so can a bit of moisture that freezes which sometimes causes the intermittent problem. Let the car sit for a while, (it melts) then the owner comes back out starts the car, and everything works fine until it happens again. Pulling a *good* vacuum on the system and refilling with refrigerant often solves this. If that is the cause of the problem.

Fortunately or Unfortunately, when someone changes out the compressor and dryer, usually a vacuum is pulled and new refrigerant is replaced. So then when things start working everybody just says "Yeah, it was the compressor"

** Note: Had they looked at the pressures with a guage set during diagnosis, they probably would have noticed that the High Side was too high and the low side was too low when the problem was occurring. And then pressures would be correct when the problem was not presenting.

Either way, if the AC is working again, I guess the problem is resolved. =)

 

I will be picking up a set of gages in a few days to check the pressures. I will post up what I find out and see what everyone thinks. I have no idea what the pressures are supposed to be on this car. And I am sure the outside temperature at the time I check it will need to be factored in as well.

Thanks for the info on the expansion valve.

 

Yes, the refrigerant valve is on the compressor itself.

 

Not the expansion valve, that's a separate issue. The RCV in the compressor varies the effective displacement of the compressor to match desired pumping loads, all in the sake of improving economy. Having a compressor running 100% and then turning it on and off, and relying on a TXV to balance flow, is less precise than altering the amount of pumping going on in the compressor, running the compressor at 30% if that's all it needs reduces load on the engine and consequently fuel consumption/emissions.

The RCV, if stuck closed or otherwise failing, will result in little pumping action, meaning high side too low and low side too high. Good working pressures will be something like 25-35 low, 150-180 high, temperature dependent, but with the variable compressor it may not be that far apart if they compressor is being run at low load. This is where a scanner comes in handy, along with your gauges, you can watch evaporator temperature sensor values and compressor demand levels, and see them change as they should or not, and know what's working and what isn't.

 

ItalianJoe1: Thanks for your knowledge of the variable displacement compressor design!
Apparently I'm going to have to do a lot of updating my knowledge to service these systems, whenever it comes time.

BTW-It sounds like that RCV failure mode is similar in symptoms to a failed compressor.(IE: high side too low + low side too high)
Can you easily change just that valve?