JensH
Senior Member
Excuse the length of the post, but I hope this thread may help anyone out there who has the “Diavia” branded dealer-at-new or post-delivery fitted A/C in a W124. Since acquiring my ’95 (’96 registered) facelift E280 4-speed auto estate last October, I have been trying to get to the bottom of poor function air-conditioning; main symptoms, lack of adequate cooling and inconsistent operation, including warm air instead of cold. My various issues and blind alleys are covered in earlier posts.
I have now sorted my problems, subject to a final service of the system by an independent A/C expert, so thought I would share some points, not least because information on the Diavia systems is patchy, to say the least.
The Diavia brand is now part of the Webasto group, and many parts are still readily available, including receiver/driers, pressure switches, compressors (at least compatible ones), resistors, sensors and probes. The original Diavia CU is NOT available.
http://diavia.it/eng_spares.php.
I have a fair amount of information, including the final piece of my jigsaw puzzle, which I found on a Russian website, which is the original Diavia instruction guide (limited) with parts listings of both components and electrical elements, although no wiring diagrams (I call this the “Diavia Spec”). I have this is a PDF and it has been really useful. I have also done my own logical wiring diagram, although I stress this is based on layout, components, connections and wire colours rather than the usual wiring diagram + symbols (in other words it a puzzle-solver’s diagram not an electrician’s).
One thing that is worth flagging up straight away from the Diavia Spec is that it states “The quantity of gas 134a necessary for charging the system is Kg 0.350”. This may surprise some people. I have seen threads suggesting Kg 1.000 or 0.850 and had the car re-gassed at Kg 1.000 myself earlier in the year (it is the default if you input the E280 92-95 model number to an A/C cleaner/gasser) – so one of my problems has been over-pressurisation, which I suspect has done for my pressure switch. I had this corrected yesterday. Kg 0.350 seems low, though.
To be clear, I am talking about a ‘3 central button’ A/C system with dual temperature zones, NOT the horizontal button automatic climate control system and layout for a RHD car.
DIFFERENCES BETWEEN MB AND DIAVIA SYSTEMS
My efforts weren’t helped by the fact that for several months I was under the impression, because that’s what MB customer services had told me by e-mail, that my car had a factory-fitted A/C system. I challenged them on this after I had dug around for some time under the dash, around the wiring, and on the web and MB then confirmed it was not factory fit.
If you are on the EPC (I am) you may find it only partially helpful, because data for your VIN may lead you to assume you have factory specification components, when, in fact, you have conversion parts. One example is EPC 54/121, body-mounted cable harness. If you have a Diavia system, you will have a SIMILAR harness or combination of looms, but not the SAME harness as the MB ‘Tempmatik’ system (see below).
These are the main differences:
1 A/C CU: From the dash you could assume factory-fitted A/C because of the controls; especially the 3 buttons, humidifier, EC and recirculation. In fact, whereas a factory system will have the CU integrated into the control module behind the controls in the centre console, the Diavia system has the standard heating control module, and a 12-pin ribbon connector, which runs to an A/C specific CU mounted under the O/S dash. Mine is Diavia part number 132061, exactly as listed on the Diavia Spec. This CU has three connectors; 12-pin (ribbon), 8-pin and 24-pin. On my car the 8-pin handles 6 wire connections, the 24-pin, 17 connections. I have a rogue MB connector, which is left unconnected, the red wire & connector part number suggests it is one of the two heat exchanger temperature sensors, or the feeler blower sensor. Still to get to the bottom of this exactly;
Working back from the front of the car:
2 Auxiliary Fans: The Diavia system has 2 auxiliary fans as per the MB system, but they operate on different principles with a different electrical schematic. The MB fans run at low speed with A/C on and switch to high speed if either (i) refrigerant pressure exceeds the switch sensor threshold or (ii) engine coolant temperature exceeds 110º. The Diavia system runs at high speed only (so not at low, simply because the A/C is ‘on’), triggered the same way. This may explain the relatively low pressure specification for the Diavia system (if their fans are intended to kick in at one (high) speed fairly soon in A/C mode). This means that the Diavia system may cause your engine to run hotter than MB with A/C on, whilst your car will be quieter! My remaining issue is that my fans do not, apparently, engage at all, although I know they work (see below);
3 Resistor: MB system has one for the fans, located behind the N/S headlamp housing. The Diavia system doesn’t (no low speed and wired directly to its own single relay);
4 Pressure Switch: This is located immediately by the receiver/dryer unit, behind the N/S headlamp housing. MB system has 2 pressure switches, low and high, each serviced by a 2-pole connection. Diavia system has one 4-pole connector to a single switch unit;
5 Compressor: On the Diavia system, this will be a Diavia component, possibly part number 084014218. On my car, the compressor has been replaced (2012) with a Seiko-Seiki SS121, with a 120 mm diameter pulley. On my car this replacement appears to have rendered redundant a 4-pole connector, which has been taped off (possibly compressor RPM-related?). The wiring from this connector feeds directly to the 8-pin socket on the Diavia CU. This has been an element in my problems (see below);
6 Fan Relays: The MB system has two, 15A and 30A, for low and high speed, mounted either in the relay tray within the fuse box, engine bay O/S or ahead of the firewall N/S on late models. The Diavia system has a single dual switch relay with a 30A fuse mounted on the suspension strut housing in front of the battery;
7 Pollen Filter: An option for MB system, not present in Diavia system.
HOW YOU WILL KNOW YOU HAVE A DIAVIA SYSTEM
1 If you have a factory data card, air-conditioning will not appear as a factory option – you won’t have code 580;
2 You will not have any of the components set out above as specific only to the MB system – fan resistor, 2 x relays, 2 x pressure switches;
3 You will have a single relay mounted near the battery and you will be able very easily to trace the 2 x auxiliary fan wiring back to this relay through a sleeve (blue, brown, light blue, brown wires) running from the front of the engine bay. The relay will have a 30A blade fuse clipped to the side;
4 By reason of 2 and 3, if you have an MB system your fans will engage when you switch A/C on (‘EC’ button off). On the Diavia system they won’t. They will only engage if refrigerant pressure drops too low or the coolant gets over-hot;
5 You will have an 11-way multi-connector, which Diavia supplied as part of its kit, to accommodate linkage between the inboard wiring and engine-bay wiring, sitting adjacent to the battery – this may be clogged with dirt and grease if it has never been cased, which may result in signal problems and faults. This connector handles the compressor and pressure switch signals and the return from the Diavia CU to the fan relay, as well as a couple of other connections and 2 earths (not connected in my car);
6 If you investigate behind your centre console you will find you have a standard heating controller modified by a ribbon cable feeding a 3-button unit which slots into place in replacement of the non-A/C single recirculation button. If you follow the ribbon, or take the dash trim and panels off, you will find your Diavia CU to the right of your steering column under the dash. The CU has the Diavia graphic logo, which is a half sun and half snow crystal framed in a “D”;
7 If you inspect the top of your heater blower box, it will have the Diavia (letters) logo on the casing.
MY ISSUES, SOLUTION & OUTSTANDING FAULTS
I had poor or no refrigeration and inconsistent operation, including regular warm air when on a cold setting. I now finally have nice cold A/C, which responds correctly to the heating regulators.
I have replaced:
1 The duo-valve with a recon unit;
2 The heating controller, again with a recon unit, although I first made the mistake of buying the MB specified A/C controller (A 124 830 38 35) instead of the standard heating controller (A 124 830 27 85), then DIY modified to accommodate the ribbon connection and 3-button module.
Had I known what I know now, I might not have needed to replace either the duo-valve or the heating controller, but doing so has definitely improved the heating.
I also replaced the gunged up Diavia multi-connector, with a new 12-way connector, re-crimping all the wire connections. I then DIY’d a water-resistant casing, to avoid future problems with dirt and grease.
My fans have never worked. I found, through a process of trial and error, that I could trigger the fans with some lateral force on the relay, although they went off as soon as the pressure was released. This suggested some kind of local connection issue or a faulty relay, so I replaced the relay housing, bracket and the relay itself (which is a standard bi-switch). That did not, however, result in functioning fan-switching, as far as I can tell.
I had not appreciated until the last couple of days, that the compressor clutch was not engaging when the A/C was turned on, and this may have been a problem for some time.
Having found the Diavia Spec, I arranged for the car to be re-gassed at Kg 0.350. Following this, I found both that the compressor clutch was not switching and then that the fans were still not switching either. I suspect that several months of too high pressure has damaged the pressure switch.
I tested the compressor with direct power; clutch engaged – so this suggested a wiring/connection issue or two.
I cured the compressor problem, after re-patching the multi-connector and looking at the wiring logically. For reasons that are not yet entirely clear to me, removing the 8-pin connector from the Diavia CU (carrying wiring from the not used 4-pole connector referred to above) cured the compressor clutch on/off issue, which now synchronises to A/C on/off. Result = cold air! If I reconnect the 8-pin connector, the clutch immediately goes off.
I let the A/C run with the car stationery, to see whether the fans would kick in. They didn’t, but I am not sure the engine coolant actually hit 110º, although it was bubbling (!). I will test again, but suspect that I have some kind of connection problem or need to replace the pressure switch, subject to testing. Funnily enough, I now cannot trigger the fans with gentle pressure on the relay (whether the old or new one). The pressure switch wiring feeds through to the 24-pin CU connector. The fan relay is fed by a blue/wire fed from the multi-connector. Since the only connections to the relay are red direct from positive pole, blue live from fan 1, light blue live from fan 2, brown from pressure switch and blue/white from inboard which must be return from a CPU triggered by either the pressure switch or coolant temp, I think I need to follow the blue/white…
So, having finally made some sense of my Diavia system, my particular problems appear to have been solely sensor/signal and wiring/connection related. Since I know both fans work, I reckon I will resolve the switching problem shortly, either by myself of with the help of the engineer. Will update… ☺
I have now sorted my problems, subject to a final service of the system by an independent A/C expert, so thought I would share some points, not least because information on the Diavia systems is patchy, to say the least.
The Diavia brand is now part of the Webasto group, and many parts are still readily available, including receiver/driers, pressure switches, compressors (at least compatible ones), resistors, sensors and probes. The original Diavia CU is NOT available.
http://diavia.it/eng_spares.php.
I have a fair amount of information, including the final piece of my jigsaw puzzle, which I found on a Russian website, which is the original Diavia instruction guide (limited) with parts listings of both components and electrical elements, although no wiring diagrams (I call this the “Diavia Spec”). I have this is a PDF and it has been really useful. I have also done my own logical wiring diagram, although I stress this is based on layout, components, connections and wire colours rather than the usual wiring diagram + symbols (in other words it a puzzle-solver’s diagram not an electrician’s).
One thing that is worth flagging up straight away from the Diavia Spec is that it states “The quantity of gas 134a necessary for charging the system is Kg 0.350”. This may surprise some people. I have seen threads suggesting Kg 1.000 or 0.850 and had the car re-gassed at Kg 1.000 myself earlier in the year (it is the default if you input the E280 92-95 model number to an A/C cleaner/gasser) – so one of my problems has been over-pressurisation, which I suspect has done for my pressure switch. I had this corrected yesterday. Kg 0.350 seems low, though.
To be clear, I am talking about a ‘3 central button’ A/C system with dual temperature zones, NOT the horizontal button automatic climate control system and layout for a RHD car.
DIFFERENCES BETWEEN MB AND DIAVIA SYSTEMS
My efforts weren’t helped by the fact that for several months I was under the impression, because that’s what MB customer services had told me by e-mail, that my car had a factory-fitted A/C system. I challenged them on this after I had dug around for some time under the dash, around the wiring, and on the web and MB then confirmed it was not factory fit.
If you are on the EPC (I am) you may find it only partially helpful, because data for your VIN may lead you to assume you have factory specification components, when, in fact, you have conversion parts. One example is EPC 54/121, body-mounted cable harness. If you have a Diavia system, you will have a SIMILAR harness or combination of looms, but not the SAME harness as the MB ‘Tempmatik’ system (see below).
These are the main differences:
1 A/C CU: From the dash you could assume factory-fitted A/C because of the controls; especially the 3 buttons, humidifier, EC and recirculation. In fact, whereas a factory system will have the CU integrated into the control module behind the controls in the centre console, the Diavia system has the standard heating control module, and a 12-pin ribbon connector, which runs to an A/C specific CU mounted under the O/S dash. Mine is Diavia part number 132061, exactly as listed on the Diavia Spec. This CU has three connectors; 12-pin (ribbon), 8-pin and 24-pin. On my car the 8-pin handles 6 wire connections, the 24-pin, 17 connections. I have a rogue MB connector, which is left unconnected, the red wire & connector part number suggests it is one of the two heat exchanger temperature sensors, or the feeler blower sensor. Still to get to the bottom of this exactly;
Working back from the front of the car:
2 Auxiliary Fans: The Diavia system has 2 auxiliary fans as per the MB system, but they operate on different principles with a different electrical schematic. The MB fans run at low speed with A/C on and switch to high speed if either (i) refrigerant pressure exceeds the switch sensor threshold or (ii) engine coolant temperature exceeds 110º. The Diavia system runs at high speed only (so not at low, simply because the A/C is ‘on’), triggered the same way. This may explain the relatively low pressure specification for the Diavia system (if their fans are intended to kick in at one (high) speed fairly soon in A/C mode). This means that the Diavia system may cause your engine to run hotter than MB with A/C on, whilst your car will be quieter! My remaining issue is that my fans do not, apparently, engage at all, although I know they work (see below);
3 Resistor: MB system has one for the fans, located behind the N/S headlamp housing. The Diavia system doesn’t (no low speed and wired directly to its own single relay);
4 Pressure Switch: This is located immediately by the receiver/dryer unit, behind the N/S headlamp housing. MB system has 2 pressure switches, low and high, each serviced by a 2-pole connection. Diavia system has one 4-pole connector to a single switch unit;
5 Compressor: On the Diavia system, this will be a Diavia component, possibly part number 084014218. On my car, the compressor has been replaced (2012) with a Seiko-Seiki SS121, with a 120 mm diameter pulley. On my car this replacement appears to have rendered redundant a 4-pole connector, which has been taped off (possibly compressor RPM-related?). The wiring from this connector feeds directly to the 8-pin socket on the Diavia CU. This has been an element in my problems (see below);
6 Fan Relays: The MB system has two, 15A and 30A, for low and high speed, mounted either in the relay tray within the fuse box, engine bay O/S or ahead of the firewall N/S on late models. The Diavia system has a single dual switch relay with a 30A fuse mounted on the suspension strut housing in front of the battery;
7 Pollen Filter: An option for MB system, not present in Diavia system.
HOW YOU WILL KNOW YOU HAVE A DIAVIA SYSTEM
1 If you have a factory data card, air-conditioning will not appear as a factory option – you won’t have code 580;
2 You will not have any of the components set out above as specific only to the MB system – fan resistor, 2 x relays, 2 x pressure switches;
3 You will have a single relay mounted near the battery and you will be able very easily to trace the 2 x auxiliary fan wiring back to this relay through a sleeve (blue, brown, light blue, brown wires) running from the front of the engine bay. The relay will have a 30A blade fuse clipped to the side;
4 By reason of 2 and 3, if you have an MB system your fans will engage when you switch A/C on (‘EC’ button off). On the Diavia system they won’t. They will only engage if refrigerant pressure drops too low or the coolant gets over-hot;
5 You will have an 11-way multi-connector, which Diavia supplied as part of its kit, to accommodate linkage between the inboard wiring and engine-bay wiring, sitting adjacent to the battery – this may be clogged with dirt and grease if it has never been cased, which may result in signal problems and faults. This connector handles the compressor and pressure switch signals and the return from the Diavia CU to the fan relay, as well as a couple of other connections and 2 earths (not connected in my car);
6 If you investigate behind your centre console you will find you have a standard heating controller modified by a ribbon cable feeding a 3-button unit which slots into place in replacement of the non-A/C single recirculation button. If you follow the ribbon, or take the dash trim and panels off, you will find your Diavia CU to the right of your steering column under the dash. The CU has the Diavia graphic logo, which is a half sun and half snow crystal framed in a “D”;
7 If you inspect the top of your heater blower box, it will have the Diavia (letters) logo on the casing.
MY ISSUES, SOLUTION & OUTSTANDING FAULTS
I had poor or no refrigeration and inconsistent operation, including regular warm air when on a cold setting. I now finally have nice cold A/C, which responds correctly to the heating regulators.
I have replaced:
1 The duo-valve with a recon unit;
2 The heating controller, again with a recon unit, although I first made the mistake of buying the MB specified A/C controller (A 124 830 38 35) instead of the standard heating controller (A 124 830 27 85), then DIY modified to accommodate the ribbon connection and 3-button module.
Had I known what I know now, I might not have needed to replace either the duo-valve or the heating controller, but doing so has definitely improved the heating.
I also replaced the gunged up Diavia multi-connector, with a new 12-way connector, re-crimping all the wire connections. I then DIY’d a water-resistant casing, to avoid future problems with dirt and grease.
My fans have never worked. I found, through a process of trial and error, that I could trigger the fans with some lateral force on the relay, although they went off as soon as the pressure was released. This suggested some kind of local connection issue or a faulty relay, so I replaced the relay housing, bracket and the relay itself (which is a standard bi-switch). That did not, however, result in functioning fan-switching, as far as I can tell.
I had not appreciated until the last couple of days, that the compressor clutch was not engaging when the A/C was turned on, and this may have been a problem for some time.
Having found the Diavia Spec, I arranged for the car to be re-gassed at Kg 0.350. Following this, I found both that the compressor clutch was not switching and then that the fans were still not switching either. I suspect that several months of too high pressure has damaged the pressure switch.
I tested the compressor with direct power; clutch engaged – so this suggested a wiring/connection issue or two.
I cured the compressor problem, after re-patching the multi-connector and looking at the wiring logically. For reasons that are not yet entirely clear to me, removing the 8-pin connector from the Diavia CU (carrying wiring from the not used 4-pole connector referred to above) cured the compressor clutch on/off issue, which now synchronises to A/C on/off. Result = cold air! If I reconnect the 8-pin connector, the clutch immediately goes off.
I let the A/C run with the car stationery, to see whether the fans would kick in. They didn’t, but I am not sure the engine coolant actually hit 110º, although it was bubbling (!). I will test again, but suspect that I have some kind of connection problem or need to replace the pressure switch, subject to testing. Funnily enough, I now cannot trigger the fans with gentle pressure on the relay (whether the old or new one). The pressure switch wiring feeds through to the 24-pin CU connector. The fan relay is fed by a blue/wire fed from the multi-connector. Since the only connections to the relay are red direct from positive pole, blue live from fan 1, light blue live from fan 2, brown from pressure switch and blue/white from inboard which must be return from a CPU triggered by either the pressure switch or coolant temp, I think I need to follow the blue/white…
So, having finally made some sense of my Diavia system, my particular problems appear to have been solely sensor/signal and wiring/connection related. Since I know both fans work, I reckon I will resolve the switching problem shortly, either by myself of with the help of the engineer. Will update… ☺
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