Jaguar XJ Aircon Types Delanair FAQs

Q. I have heard that Jaguars use different types of A/C units, so which one are we talking about here?

A. Basically the Air Con system is of a standard design on all Delanair equipped Jaguars.  The difference referred to is the Air Delivery Unit (ADU) and is often misleadingly referred to as the Air Con unit or system (even by some respected engineers on other Jaguar related sites and Jaguar parts catalogues). This part is responsible, as the name suggests, for the delivery of air at the required temperature or if you prefer it’s the control panel part of the Air Con system but it is most defiantly is not the whole system, rather just another component like the Compressor or Condenser which are also just parts of the whole

But to clarify further we will describe the different units. Most of the XJ range, which were one of the cars that first had Air Con, used a unit manufactured by Delanair. The Mk 1 was fitted to the Series I XJ6 and XJ12 and was controlled by bellows and vacuum solenoids and wasn’t terribly efficient but was better than nothing at all. The experience we have had with this unit is slightly limited But in most cases the faults seem to be as with any other Air Con system, but with the exception that the bellows nearly always leak and the only solution we have had any luck with is to ether replace them (very rare) or fix them with bicycle inner tube repair kits and/or silicon sealant.

The Mk. II was first introduced in the early 70’s appearing most notably in the XJ-S in 1976 and the Series II XJ6/12. This unit is controlled by an electronic amplifier feed from thermostats and sensors that control the temperature range via an electronic servo and vacuum switches. The cooling (or heating) is directed out of the air vents by actuating rods which are notorious for becoming mis adjusted and can cause all sorts of issues. They are for the most part fairly easy to repair and have been given much press in the past on how to get the best from them. We are lucky enough to have the diagnostic Tester built by Pektron of Derby, England, which enables us to find faults following a comprehensive flow chart of instructions. This tool simply fits in series with the system and is controlled by a set of switches, knobs and flashing LEDs’ that tell the technician what’s happening.

The Mk. III Delanair is a completely different animal and is by far the best unit. Introduced into the 1987 ½ MY (model year) XJ-S and the early XJ40s, this one is totally electronic. Incidentally; 1987 ½ MY XJ-S is not a definite date as we have found this unit fitted to earlier cars and even the parts catalogues aren’t clear as they state its only fitted from VIN 139052 but we have seen it fitted in a 136xxx car although it may have been retrofitted following a warranty claim earlier in it’s life as they are possibly swappable with a bit of work on the looms! The MK.III uses an Electronic Control Unit ECU (Rachael just said – “oh that’s what ECU stands for” – glad to be of service) The ECU gets its signals from similar thermometers and sensors to the MK. II and is directly controlled by the function switch and temperature select dial. Also most notably the unit has a manual override activated by pulling the temperature knob out. This puts the system into a hotter/colder cycle and ignores the ambient temperature. The ECU sends signals to the motorised flaps to direct the airflow with the exception of the screen vent, which is still controlled in the conventional vacuum style actuator, as is the water valve, which is the same on the MK.II. It’s worth mentioning that, we have had three cars in at the beginning of autumn (fall for you Americans) with their Water valves stuck firmly closed which is odd as most State side shops get them with it stuck open.

Delanair were dropped by Jaguar by the time the X-type, S-type 2 and X300 came out, probably due to the influence of Ford wanting to keep friends with their existing cars suppliers. So these cars are fitted with a totally electronic unit and it has to be said are, so far a reliable unit (but it’s early days – lets see how they are going in twenty years). The main problem area seems to be with the control interface suffering from faulty switches and display. As parts for these are still readily available fault repairs have so far been fairly easy if a little time consuming.

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