Air conditioner - pressure control valve replacement
Thread Starter
Member
Joined: Apr 2022
Posts: 136
Likes: 34
GL320 2007
Air conditioner - pressure control valve replacement
Just a post in case anyone else has a problem:
Main symptoms:
it takes a long time to start blowing cool air on hot/warm days. Mine would take a couple of kms of driving.
AC struggles on hot days. May completely stop cooling.
solution:
Assuming your compressor is not making a dry clutch noise, then it’s likely the pressure control valve on the compressor has/is failing. Basically it won’t allow the compressor to build pressure. I’m told it controls suction pressure, so more likely you’ll see higher suction pressures and less expansion over the evaporator.
I have a RHD vehicle, so it was an easy swap. I did it with compressor in the car. I had enough room to do this with non-right angle circlip pliers. Basically squeezing hand up through the lower control arm.
steps:
degas car. Note if you have a dual system, you need to hold a vacuum for awhile, otherwise it keeps building pressure. I pulled mine straight after a degas.
remove electrical connector from valve.
remove circlip
get some pliers and try and rotate the valve to loosen.
Use pliers to pull it out. It takes some force here.
push new valve in. You won’t be able to seat it fully. I used a socket to place over the connector, with extension piece. Then tapped the extension piece with a hammer to seat it.
replace circlip.
replace electrical connector.
regas
It took me 45 mins. About 20 min was finding pliers to get a grip on the valve. Another 10 mins working out how to access it. Overall a pretty simple job.
make sure you get one with a diode. Apparently some early cars may not have a diode. Mine was 2007 so I don’t think so.
Main symptoms:
it takes a long time to start blowing cool air on hot/warm days. Mine would take a couple of kms of driving.
AC struggles on hot days. May completely stop cooling.
solution:
Assuming your compressor is not making a dry clutch noise, then it’s likely the pressure control valve on the compressor has/is failing. Basically it won’t allow the compressor to build pressure. I’m told it controls suction pressure, so more likely you’ll see higher suction pressures and less expansion over the evaporator.
I have a RHD vehicle, so it was an easy swap. I did it with compressor in the car. I had enough room to do this with non-right angle circlip pliers. Basically squeezing hand up through the lower control arm.
steps:
degas car. Note if you have a dual system, you need to hold a vacuum for awhile, otherwise it keeps building pressure. I pulled mine straight after a degas.
remove electrical connector from valve.
remove circlip
get some pliers and try and rotate the valve to loosen.
Use pliers to pull it out. It takes some force here.
push new valve in. You won’t be able to seat it fully. I used a socket to place over the connector, with extension piece. Then tapped the extension piece with a hammer to seat it.
replace circlip.
replace electrical connector.
regas
It took me 45 mins. About 20 min was finding pliers to get a grip on the valve. Another 10 mins working out how to access it. Overall a pretty simple job.
make sure you get one with a diode. Apparently some early cars may not have a diode. Mine was 2007 so I don’t think so.
Thread Starter
Member
Joined: Apr 2022
Posts: 136
Likes: 34
GL320 2007
Valve costs $50, denso compressor $800. All AUD. I decided to do the valve as it was significantly cheaper. I don’t hear of many actual compressor failures (ie spraying metal through the system and needing a lot of flushing)
Newbie
Joined: Aug 2021
Posts: 9
Likes: 4
W211
AC Compressor Control Valve DIODE
"...make sure you get one with a diode. Apparently some early cars may not have a diode. Mine was 2007 so I don’t think so."
Good advice there. I was happily sold two different control valves without a diode for my 2003 W211, they don't work. Control valve WITH diode has a colored sticker or painted circle on the end.
Look for diodes in solenoid circuits for things like relays or electric pressure control valves. When you energize a solenoid, current flows through the windings of an electromagnet. When you de-energize that solenoid, the field collapses and current wants to flow back the other way. That back-flow can report incorrect sensor values in your Mercedes. And in your pinball machine the current backflow will cause arcing across the contacts of the flipper activation buttons when you release the flipper button. A diode prevents current backflow when a solenoid magnetic field collapses, reducing wear at the solenoid activation switch contacts.
"Geek till it Mhz!"
Good advice there. I was happily sold two different control valves without a diode for my 2003 W211, they don't work. Control valve WITH diode has a colored sticker or painted circle on the end.
Look for diodes in solenoid circuits for things like relays or electric pressure control valves. When you energize a solenoid, current flows through the windings of an electromagnet. When you de-energize that solenoid, the field collapses and current wants to flow back the other way. That back-flow can report incorrect sensor values in your Mercedes. And in your pinball machine the current backflow will cause arcing across the contacts of the flipper activation buttons when you release the flipper button. A diode prevents current backflow when a solenoid magnetic field collapses, reducing wear at the solenoid activation switch contacts.
"Geek till it Mhz!"
Thread Starter
Member
Joined: Apr 2022
Posts: 136
Likes: 34
GL320 2007
No idea, but I'd be nervous. It talks about BMW/Audi, but not Mercedes. You can wire in a diode separately, but that would be a PITA.
I bought this one: https://www.ebay.com.au/itm/334663157636
It came with a yellow dot on the top which is supposed to indicate diode. I couldn't get any idea of who made these or whether any were produced by 'reputable' companies. It's likely that most of them are rebranded. Mine had no brand on it. The one I took out had no brand, but did have a code on it. I'll try to remember to take photo of it.
I bought this one: https://www.ebay.com.au/itm/334663157636
It came with a yellow dot on the top which is supposed to indicate diode. I couldn't get any idea of who made these or whether any were produced by 'reputable' companies. It's likely that most of them are rebranded. Mine had no brand on it. The one I took out had no brand, but did have a code on it. I'll try to remember to take photo of it.
Super Member
Joined: Jan 2007
Posts: 622
Likes: 202
From: CA
11 ML550, 95 Supra TT, 14 Audi S4
Many replacement compressors don't come with the diode. I had mine done at the dealer and it never worked properly until I discovered the diode issue. It can be added pretty easily after the fact if the valve/compressor doesn't have one: https://mbworld.org/forums/gl-class-...-9006-a-2.html
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From: Emmett, ID, USA
2007 GL450
High Side - Low Side
High - Low Normal
Low-Low Low on refrigerant, possibly other issues
High - High Overcharged, valve broken
Low - High Call an exorcist
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MBWorld Fanatic!
Joined: Jul 2012
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From: Orbiting the planet
This place is a joke.
With the age of these cars you should really be replacing the complete compressor with an OEM Denso unit. At some point the old bearings in the pulley will seize and leave you on the side of the road, or alternately the compressor will come apart internally sending metal particles throughout your AC system costing thousands of dollars to repair. This isn't the repair to try and save money on.
Last edited by E55Greasemonkey; Apr 4, 2023 at 03:37 PM.
Junior Member
Joined: Aug 2020
Posts: 18
Likes: 2
2011 GL450 4Matic
Just a post in case anyone else has a problem:
Main symptoms:
it takes a long time to start blowing cool air on hot/warm days. Mine would take a couple of kms of driving.
AC struggles on hot days. May completely stop cooling.
solution:
Assuming your compressor is not making a dry clutch noise, then it’s likely the pressure control valve on the compressor has/is failing. Basically it won’t allow the compressor to build pressure. I’m told it controls suction pressure, so more likely you’ll see higher suction pressures and less expansion over the evaporator.
I have a RHD vehicle, so it was an easy swap. I did it with compressor in the car. I had enough room to do this with non-right angle circlip pliers. Basically squeezing hand up through the lower control arm.
steps:
degas car. Note if you have a dual system, you need to hold a vacuum for awhile, otherwise it keeps building pressure. I pulled mine straight after a degas.
remove electrical connector from valve.
remove circlip
get some pliers and try and rotate the valve to loosen.
Use pliers to pull it out. It takes some force here.
push new valve in. You won’t be able to seat it fully. I used a socket to place over the connector, with extension piece. Then tapped the extension piece with a hammer to seat it.
replace circlip.
replace electrical connector.
regas
It took me 45 mins. About 20 min was finding pliers to get a grip on the valve. Another 10 mins working out how to access it. Overall a pretty simple job.
make sure you get one with a diode. Apparently some early cars may not have a diode. Mine was 2007 so I don’t think so.
Main symptoms:
it takes a long time to start blowing cool air on hot/warm days. Mine would take a couple of kms of driving.
AC struggles on hot days. May completely stop cooling.
solution:
Assuming your compressor is not making a dry clutch noise, then it’s likely the pressure control valve on the compressor has/is failing. Basically it won’t allow the compressor to build pressure. I’m told it controls suction pressure, so more likely you’ll see higher suction pressures and less expansion over the evaporator.
I have a RHD vehicle, so it was an easy swap. I did it with compressor in the car. I had enough room to do this with non-right angle circlip pliers. Basically squeezing hand up through the lower control arm.
steps:
degas car. Note if you have a dual system, you need to hold a vacuum for awhile, otherwise it keeps building pressure. I pulled mine straight after a degas.
remove electrical connector from valve.
remove circlip
get some pliers and try and rotate the valve to loosen.
Use pliers to pull it out. It takes some force here.
push new valve in. You won’t be able to seat it fully. I used a socket to place over the connector, with extension piece. Then tapped the extension piece with a hammer to seat it.
replace circlip.
replace electrical connector.
regas
It took me 45 mins. About 20 min was finding pliers to get a grip on the valve. Another 10 mins working out how to access it. Overall a pretty simple job.
make sure you get one with a diode. Apparently some early cars may not have a diode. Mine was 2007 so I don’t think so.
Gonna attempt this today but I’m in the US. AC lines in the way of removing the control valve. Gonna go get line evacuated and hopefully I won’t have to remove anything to get it out. 🤞 Will keep y’all updated.
Junior Member
Joined: Aug 2020
Posts: 18
Likes: 2
2011 GL450 4Matic
***UPDATE***
So….what I assumed were the AC lines were actually the power steering lines. They cross right over the control valve and the only way I think I can remove it is by completely unbolting the compressor and the AC lines 😩..anyone know of a simpler way of getting the control valve out without having to dismantle the compressor and AC line assembly? Trying to minimize my work load here….😄
So….what I assumed were the AC lines were actually the power steering lines. They cross right over the control valve and the only way I think I can remove it is by completely unbolting the compressor and the AC lines 😩..anyone know of a simpler way of getting the control valve out without having to dismantle the compressor and AC line assembly? Trying to minimize my work load here….😄
Last edited by MB_noob; Aug 15, 2023 at 08:06 PM.
Junior Member
Joined: Aug 2020
Posts: 18
Likes: 2
2011 GL450 4Matic
Thread Starter
Member
Joined: Apr 2022
Posts: 136
Likes: 34
GL320 2007
That sucks. I'd be looking to loosen the power steering hose and getting enough room to get the valve past. Power steering fluid is easy to replace.
I've you're going to remove compressor lines, you've got to make sure you keep it clean. Spray heaps of brake cleaner at the control valve before removing it. You want to clean any dirt from the this area so you don't drag dirt back in when you replace it.
I've you're going to remove compressor lines, you've got to make sure you keep it clean. Spray heaps of brake cleaner at the control valve before removing it. You want to clean any dirt from the this area so you don't drag dirt back in when you replace it.
Junior Member
Joined: Aug 2020
Posts: 18
Likes: 2
2011 GL450 4Matic
That sucks. I'd be looking to loosen the power steering hose and getting enough room to get the valve past. Power steering fluid is easy to replace.
I've you're going to remove compressor lines, you've got to make sure you keep it clean. Spray heaps of brake cleaner at the control valve before removing it. You want to clean any dirt from the this area so you don't drag dirt back in when you replace it.
I've you're going to remove compressor lines, you've got to make sure you keep it clean. Spray heaps of brake cleaner at the control valve before removing it. You want to clean any dirt from the this area so you don't drag dirt back in when you replace it.
**UPDATE**
So I did remove the power steering line ( had to replace the fluid so knocked two birds with one stone) and got the valve out. The shop said I was empty but the valve shot out bc there still a bit of pressure in there. Good thing I wasn’t really next to it when it blew off. Lol but got the new control valve in, rented a gauge and pump to vaccum and then filled with new Freon. Now I’m nice and cool again! 👌👍 Just in time bc the kids start school tomorrow and dropping them off hot is no bueno. 😄
If anyone needs to do this job, removing that line instead of unbolting the compressor saves a whole lot of time. Three bolts, a belt, and some AC lines vs One bolt and some PS fluid. I chose the latter. Just make sure either you evac or have a reputable shop take a look at the pressure lines. 🙈 Hope this helps!
