124 Aircon expert help needed Herts/Essex

[Keith]

I have a long standing poor performance problem with my factory aircon on a 95 E300D. Several recharges have failed to cure it also the duo valve has been changed for a new one and the control board swapped with another with no improvement. Air works but struggles to cope also temp control needs frequent manual intervention in cooler weather tp avoid over heating the cabin which it never did when i first had the car. Several merc mechanics have had a go including one of the celebs on this forum but with no luck. If there is a real expert on 124 aircon out there operating in the Herts / Essex area I would love to hear from you and challenge you to sort this out for me!

Keith

 

[Richard Moakes]

The problem sounds like control gear, rather than the aircon itself.

Trouble is, most specialists know how the basic system works, but don't know the specifics of each particular vehicle.

Were this my vehicle, I would just start testing each system and component in turn, in particular I would disable as much of the control gear as possible and 'hotwire' the system into max cooling mode. Just make sure if you do this, you NEVER bypass the high and low pressure switches, this should only be done in very specific circumstances and then only for a few seconds.

ie. Is the compressor engaging and disengaging correctly? Is the belt slip detector cutting out the compressor too soon? Plenty of info about this on the American forums.
Are the fans on the condenser engaging with high pressure and temperature?
Try hosing the condenser down with some water with the car at idle and the aircon on, it will improve the cooling of the system if it is working correctly.
Clamp off the heater line to the duovalve, make sure no hot water is flowing into the cabin, regardless of what the control board is supposed to be doing.
Check the small fan which pulls air over the temperature sensor, try some electrolube on the temperature selector variable resistors, or alternatively run them from min to max plenty of times to wipe any rubbish from the tracks.

My W124 has a Diavia R134a system with a parallel flow condensor, which is about as good as it gets with R134a, but it struggles at idle in traffic jams. On the open road, it can chill with the best of them. I regularly check the fans operate with high refrigerant pressure and/or engine temperature and also give the condenser a wash down and remove any dirt or flies etc...

I doubt you will find an expert on W124 aircon who isn't a W124 expert, which means you need to talk to people like Andy Gayle or George Fraser, but even then, I expect that they might subcontract recharging and leak detection to a generic aircon specialist.

Good luck with this, and remember W124 aircon (particularly R134a) is not up to the standard of modern cars with variable displacement compressors, the evaporator is not efficient enough and the condensor is not really big enough!

Regards,

Richard
1989 W124 300E

 

[BadTasteUK]

Richard, sounds like you're quite switched on with aircon, and having the same setup as me (I think), I wondered if you could assist on a problem I'm having.

I have a Diavia system, which works very well most of the time. Every now and then my temp gauge increases quite quickly in traffic (and the rad exploded at one point as well. which was replaced with a much bigger one!).

I never linked the rise in temp with the aircon until I noticed by accident that every time it happens, the three aircon buttons (dehumidify, EC, and recycle) don't light up if pressed, (indicating some loose connection or trip out as a guess).

Of course I then have to switch the engine off.

If I then leave it for ten minutes and start her up again, the temp drops to normal quickly and the aircon is back on.

My best guess is that for some reason (loose connection?, safety cut out?), the aircon system stops working, and the two fans on the aircon rad also stops working, hence the car gets hot.

I'm open to any suggestions on a way forward, preferably without spending loads of money.

Thanks for reading!

 

[Richard Moakes]

I would start by looking at the relays and fuses which are in the engine compartment. You can identify them by the fact they are the only blade fuses on the car, from memory I believe they are on the nearside inner wing.

Then I would have a look at the Diavia system controller, you will find it linked to the buttons by a grey ribbon cable, it is under the passenger footwell carpet and sound insulation, it is a small black box about 6 inches square.

I would suspect that there might be a dry soldered joint in the controller, or perhaps one of the relays or fuses has corroded.

I am surprised it gets so hot, have you checked the viscous fan coupling? Even in a traffic jam, I can put the car in neutral and get the temperature down by revving the engine up to 1500-2000rpm. Or if I am feeling lazy I just let the electric fans take care of it.

The two electric fans are controlled by a high temperature switch on the cylinder head and a high refrigerant pressure switch by the receiver dryer, so if they stop working altogether, it might be a basic electrical issue with the power supply to the aircon control unit and fans.

I don't recall where they are fed from, but if it isn't direct from the battery via those blade fuses, then I would be very surprised.

Best of luck, it doesn't sound too expensive or difficult.

 

[BadTasteUK]

Richard, thankyou for such a detailed reply; I've got lots to go on now.

I'll let you know how I get on.

Cheers,
G.

 

[BadTasteUK]

Richard, a quick update...

I had the fuse changed and disconnected/reconnected the box in the footwell (looked like a dodgy connection), and touch wood it seems to have sorted it (hope I'm not speaking too soon!)

Thankyou very much for your help!

Cheers,
G.

 

[john.clarke]

W124 aircon - bad performance

Hi....to all in Blighty.......had bad performance problem. Check the small grill in the roof lamp cluster. It houses the interia temperature senser. Small ceramic capacitor look-a-like, suspect it is a negative slope resister. Well it gets all gummed up with fluff etc and ceases to function properly. Just clean out with surgical alcohol. Need to unclip the whole lamp cluster as if changing a lamp. Watch the air pipe attached !

Tyke - South Africa