547
TEMPERATURE SENSORS: Martin Sellars says, “Temperature Sensors: the Delanaire system uses three, all are
electrically identical. They measure ambient air temperature (mounted on the RH blower housing), in car temperature
(above the glove box, behind a small aperture in the dash) and on the evaporator. These have three wires to them,
power (5Volts from the ACC), ground, and the output wire. The output voltage is very closely controlled at 2.785V at
0°C and rising by 0.01V per degree C. So, a sensor at 20°C (about 68°F) should read 2.985V, and at 30°C (about
90°F) should read 3.085V, and so on. I found these can be measured reasonably easily with a standard 20k/Volt
moving needle “hobby” type multimeter, at least well enought for fault finding purposes.”
Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:
“The air-conditioning in car sensor now uses the motorised aspirator/sensor from the XJ6 allowing a more accurate
reading of the true temperature of the cabin which will be less susceptible to drift or overshoot.”
DUMB PROBLEMS: Martin Sellars: “My car showed very erratic operation of the A/C, sometimes OK, sometimes
wrong settings (hot on hot days and vice versa!), sometimes no action at all. This fault might have been blamed on the
computer - but in fact it was due to moisture coming out of the evaporator, and running down the RHS of the
transmission tunnel onto the inline fuse holder that carries the supply current to the A/C computer. The contacts had
corroded slightly, breaking the supply current, and giving intermittent operation of the A/C. A new inline fuse, plus
fixing the drainage, solved the problem.”
WHILE YOU HAVE THE BLOWERS OUT: Martin Sellars: “While the blowers are out, access to the evaporator is
much easier. The four short tubes which couple the evaporator body to the rubber blower ducts can be twisted slightly
and removed. This allows slight access to extract some of the gunge and detritus that blocks up the drainage system,
causing wet carpets, rusty floors, and other problems.”
HEATER CORE REPLACEMENT: Those who must replace the heater core should thank their lucky stars if they
have the Delanair MkIII system. A major design feature of this system is the ease of replacing this core, a major task
on the earlier cars. The Delanair MkIII system has bolt-on pipes for the heater core, eliminating the need for the
“shortcut” pipe-cutting procedure devised for the earlier system. Also, Per Michael Neal, “The heater core is
removable from the right side. There is a large piece of black tape, similar to electrical tape, that covers the access
panel. Removal of the core is simple as unbolting the pipes, pulling the glovebox and access cover and removing the
core.” This eliminates the need for removing the instrument panel and dropping the steering column, as on earlier
models.
HEATER CORE PIPE ATTACHMENT BOLTS: Per Julian Mullaney, “There was a problem of dissimilar metals
causing corrosion of the bolts which attach the pipes to the brass core. The pipes and heater core are brass, the screws
holding them together were steel. I guess stainless bolts would be better. You could replace them as a preventive
measure.”
HEATER CORE PIPE ATTACHMENT O-RING SEALS: Per Julian Mullaney, “The O-ring seal used at the
connection point appears to be of a terrible design. A mechanic once told me that these O-rings always go first.”
For anyone who doesn’t think the resultant leaks would be a big deal, Mullaney adds: “This leak really screwed up a
lot of stuff under there. The drips ruined the A/C amp, connectors, and my CD player.”
Apparently Jaguar realized the seriousness of this problem. According to Michael Neal, “Jaguar has a gasket to replace
the O-rings. It is shaped like the mating pipe of the heater core and is made out of a silicon/rubber type material.” The
part number for the gasket is JLM 759; you need two to do the job.
According to Mark Roberts, the “condensation deflector shield” being added to systems by Jaguar (see page 662) is
actually a result of these connections leaking on radios!