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G320 - A/C blowing hot air

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Posted 6/25/2018 4:12 PM

gerryvz
Extreme Veteran

Date registered: Apr 2014
Location: Annapolis, MD
Vehicle(s): 1994 G320, 1989 560SEC, 1994 E500 (W124)
Posts: 336
300

G320 - A/C blowing hot air

All,

I had my A/C system in my 1995 G320 serviced last fall in Texas, just before I moved to the East Coast (Maryland) in mid-October. That mainly was to remedy a lack of the system to hold refrigerant. I had this work professionally done by a very trusted indy shop in the Houston area. The fix was as follows:

- New A/C compressor (standard and appropriate Denso unit)

- New Hansa A/C receiver-drier

- New A/C o-rings underhood

- Evacuated refrigerant

- Added 2.2 lbs R-134a and appropriate PAG oil

The A/C worked quite well, generating appropriate temperatures between 40-55F at the dash center vent.

Over the winter, and as I started using the system again this spring, it has only blown hot air.

Putting gauges on the system, it showed low pressure on the low side. Also, the compressor was not operating.

I added about 1/2 can of R-134a to the system, and brought the low side up to ~45 PSI indicated on the gauges. Immediately the compressor kicked on.

I also noticed that the electric aux fans in front of the radiator + condenser are inoperative, under any conditions. I see bubbles/refrigerant moving in the receiver-drier sight glass, and also on the sight glass in the A/C gauges.

A/C pressure gauges are still showing ~45 PSI on the low side, but the high side is only showing pressure of ~50 PSI. High side pressure is not climbing. Warm air of around 80F (same as ambient temp) continues to come from the center vents.

I notice that the high side line that goes from the fitting to the gauge gets very hot to the touch after running the system for a few minutes.

It seems that there may be some sort of blockage or other problem that is preventing the high side pressure from climbing to the expected 200-250 PSI. And I am unable to make the aux fans go on, though the compressor is running. I see the compressor running (front of the compressor is rotating when I click the dash switch into A/C mode, not rotating when the dash A/C switch is turned off), but it is not physically cycling as you'd expect/hear that it would.

I have checked the fuses (30A for the compressor; 25A for the aux fans) and they are fine. I believe the Klima relay is OK, but am not 100% sure. I will source a spare unit very shortly, to double-check this. There is dye in the system, but I am not seeing any obvious refrigerant leaks on the ground, such as from a bad evaporator.

Does anyone have any ideas as to why the system is not generating appropriate pressure on the high side, and also why the aux fans are not operating appropriately?

How can I activate the fans to see if there is a problem there?

Cheers,
Gerry

#239469

Author

Posted 6/26/2018 7:29 AM

gerryvz
Extreme Veteran

Date registered: Apr 2014
Location: Annapolis, MD
Vehicle(s): 1994 G320, 1989 560SEC, 1994 E500 (W124)
Posts: 336
300

Re: G320 - A/C blowing hot air

UPDATE

It appears that the system has developed another significant refrigerant leak.

First off, I checked the accuracy of my gauges on my E500 — all just fine. The E500 W124 has always had great A/C, never a problem with it. Everything good with the gauge set.

Put the gauges back on the G-wagen. Added a full can of 134a. Interestingly, that brought things up to around 200 PSI on the high side, and about 30 on the low side. Ambient was about 85F. Not quite a full charge, but I was out of 134a after adding that can.

After adding the can, I started getting MUCH cool(er) air from the center vents. Took the truck out to get a couple more cans of 134a. A/C worked fine during that run. Ambient temp was around 82F.

I added another 1/2 can of 134a after I got home, and the system appears to be operating normally now. Pressures came up to around 40 PSI on the low side and 225 PSI on the high side in 82F ambient temp. I took the truck out for another run and it was blowing cold air as normal, and plenty of condensate (water) on the ground underneath (another good sign). I could see pressures fluctuating on the gauges as the compressor kicked in, as well.

Temps at the center vent were 45-55F depending on if I was moving or sitting in traffic.

So, it appears that the system was just almost totally down on refrigerant. Total added was about 18-20 oz. That’s a lot of refrigerant loss, so a pretty good leak. I have not added any “stop leak” to the system.

There is already dye in the system from last fall, and I also have an electronic leak detector, so it looks like I now have to go into detective mode to find the leak.

Overall, the system in my G appears to be pretty much like the 124 system, although being gray-market, it has manual fan and temp control rather than the ACC. As I mentioned, the expansion valve and compressor are identical to regular late 124 stuff. The evaporator, heat exchanger and condenser do appear to be G-wagen specific parts.

Depending on what I find with the leak detection, I still think I’ll have to totally evacuate the system to replace any needed component. From there at least I will have a starting point for adding new refrigerant and oil in known quantities.

Cheers,
Gerry

#239475 - in reply to #239469

Author

Posted 6/26/2018 5:00 PM

fernweh

Date registered: Apr 2006
Location: Calabasas, CA - Centenario, BCS - Luebeck, Germany
Vehicle(s): Few Mercedes-Benz, a Toyota Amphibious and a Vespa
2000

RE: G320 - A/C blowing hot air

Gerry,

I am trying to remember the a/c set up in my Europa 300GE......not so easy anymore.

At one time I had the a/c system checked out at a local only a/c repair place (no fancy place), they evacuated the system, and replaced the freon (R134).

When we finally started the engine, the aux fans would not come on, and the a/c pressure was going very high. The a/c guy immediately applied separate power to the aux fans,

and as soon the fan ran, cooling off the radiator, the a/c pressure dropped to normal level. The guy just pointed to the electrical switch at the dryer.......

So I went to my parts place to order a new switch. I could not get the correct switch, nothing seemed to match up.....

Eventually I found out something interesting, who ever (Europa?) converted the a/c system to the new/required R134 freon, did not change out the dryer, and the existing fan switch did not work with the R134 system.

Like I said before, do not remember the correct details, but one switch worked on temperature, while the other was a pressure switch. As soon as I installed now the correct switch, the a/c system worked flawless, and the aux fans came on,

and cycled as needed, actuated by coolant temp or a/c pressure.

#239482 - in reply to #239469

Author

Posted 7/2/2018 5:03 PM

H1LM002G55
Expert

Date registered: Mar 2010
Location: S Florida / Geneva / Jeddah
Vehicle(s): 500 GE, G55, LM002, H1
Posts: 1796
1000

Re: G320 - A/C blowing hot air

Search for my posts about how to find a Mobile HVAC tech with an electronic leak detector.

I'd wager it is an issue with the expansion valve or your condenser has cracked due to the rubber vibration mounts being old.

#239521 - in reply to #239469

Author

Posted 7/2/2018 5:08 PM

H1LM002G55
Expert

Date registered: Mar 2010
Location: S Florida / Geneva / Jeddah
Vehicle(s): 500 GE, G55, LM002, H1
Posts: 1796
1000

Re: G320 - A/C blowing hot air

https://www.macsw.org

Use them to find a tech that knows automotive AC systems with proper diagnostic equipment...not UV dye!

#239522 - in reply to #239469

Author

Posted 7/4/2018 12:02 PM

kiato4
Veteran

Date registered: Aug 2013
Location: New York, NY
Vehicle(s): 1995 G320, 1985 190E 2.3-16
Posts: 161
100

Re: G320 - A/C blowing hot air

If this is a 1995 G320 like mine, it originally had R134a from the factory. I also have a leak that between summers requires a top up of Freon after installing a new compressor, new receiver/dryer, and even a new expansion valve (mine was not allowing the G to blow cold at idle).

I would add that proper aux fan operation is critical to the G blowing cold AC, I remember when we were trying to diagnose the issue that led to the bad expansion valve that whenever running without the fans it simply would not cool well even when driving the G at speed and with full Freon. There simply is not much room in the G320 engine bay for air to cool the condenser without fans.

One thing I've wanted to think about is either install a stronger fan or a larger condenser to get the G even cooler, it clearly is 1990s technology and not even close to as comfortable as a newer G. My 1995 Range Rover Classic LWB on the other hand was a worse truck overall but had a frigid AC, that is the only thing that Rover got right in comparison to the G320.

#239532 - in reply to #239469

Author

Posted 7/8/2018 6:56 AM

gerryvz
Extreme Veteran

Date registered: Apr 2014
Location: Annapolis, MD
Vehicle(s): 1994 G320, 1989 560SEC, 1994 E500 (W124)
Posts: 336
300

Re: G320 - A/C blowing hot air

Yes, my truck is R-134a from the factory. A/C has been running just fine since I re-charged everything, so it is apparent there is a leak in the system somewhere, that i will need to find.

Over the past week we had very very warm temperatures here in Maryland, daily was pushing 93-98F ambient temps with extremely high humidity. Very very similar to what I saw in the Houston area for 6-7 months per year.

The A/C struggled to keep up with the 90+F temps, just as it did in Texas. Yesterday, when temps were down in the 80sF ambients with less humidity, the A/C just about froze me out of the truck !!

#239542 - in reply to #239469

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