Jaguar XJS Blower Motor Not Working
On the XJS a blower that won't blow is usually the small speed-control board inside the blower itself — its power transistor fails and leaves high speed only, or shorts and won't let the fan stop. Worn motor brushes and debris come next, then relays and fuse holders. I'd test each blower on its own first by pulling the other side's fuse.
How bad is it · Safe to drive
Safe to drive — as long as you can keep the screen clear
A dead blower is mostly a comfort problem, but without it the screen can mist up and stay misted. A blower that runs with the key out will flatten the battery, so pull its fuse until it's fixed.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
The speed-control board inside the blower — only high speed works
From roughly 1987 each blower carries its own small board in the airflow: a Darlington power transistor gives the lower speeds and a relay bypasses it for high. The transistor fails open and the blower is left with high only. The board sits in damp air under the scuttle, so rust on the transistor and tired diodes and capacitors are common. Water is its enemy: a scuttle leak or a weeping heater matrix that wets the footwell often goes with a rusty transistor.
One blower, or both, runs only on high or defrost. With one blower dead the other pushes its air backwards through it, so the vents just puff.
Pull each blower's fuse in turn and run the other through every speed. With the system on, unplug the flat 9-wire plug at the blower and put 5 V on the middle pink wire: a good board takes the fan almost to high. Never put 12 V on that wire — it kills a good transistor.
Take the blower out and rebuild the board: a 2N6284 Darlington (later cars MJ11016), the diodes, and the small capacitor if it has failed. Seal the board with lacquer and give the motor some oil while it's out. New parts often carry no polarity marks, and the diode and the Darlington legs must go in the right way round — take the earth connection on the board as the reference.
A shorted transistor or diode — the blower won't switch off
The blowers are fed straight from the battery, and the board decides when they run. A Darlington that has failed short, or a shorted diode, runs the motor flat out with the key out. A relay stuck closed does the same, but far less often.
One blower roars on high all the time, even with the ignition off; only pulling its fuse or the battery lead stops it. A milder form is a blower that puffs for a second every few seconds with the system off: a diode whose contact has rotted off the board, or a Darlington on its way out.
Pull one blower fuse at a time to find which side it is. On the board, measure the transistor case to earth — the case is the collector and must be insulated from the board. On 1970s cars, look also at a diode in the auxiliary engine fan circuit, by the transmission tunnel in the driver's footwell: when it fails, current from the fan switch back-feeds the blower circuit. If you bench-test a blower on a home-made extension lead, check the lead's polarity first — a reversed lead runs the blower whenever it's plugged in.
Replace the Darlington, and the diodes while you're in there; the whole job is an afternoon, longer on the driver's side. A new blower unit is not needed.
The blower motor — worn brushes, seized bushes or debris
The motors are an open design. Brushes wear down, bronze bushes dry out and seize, and leaves or fibre can wrap the shaft. Damp from the A/C drains corrodes them too.
A blower that's dead on every speed, starts after a knock on the housing, or turns slowly and stops. A burning smell with the A/C on can be a motor bearing seized on its shaft and spinning in the housing.
Give the blower box a firm tap, or spin the fan by hand. Out of the car, run the motor straight off 12 V, minding the polarity: if it won't turn, the motor is at fault.
Clear the shaft, oil the bushes and pin a spinning bush with a small self-tapping screw. Brushes from a power tool, ground to size and soldered on, work; turning worn brushes round buys time. A used motor is the other way out. Look inside the squirrel cage too — a glove has been found in one. If the blower is loose but won't come out, prise the lower flap open: it moves the hidden upper flap and frees the blower. A motor, fan and bracket from an XJ40 of the same side (1987–90) bolts in.
Relays — the high-speed relay in the blower, or the Mk II relay pack
On later cars a high-speed relay lives inside each blower housing, in the damp, and rusts. Earlier Mk II cars use a pack of four relays — low, two mediums and high — whose fine coil wires break off at the terminals. Each dead relay takes out one speed. Water reaches both: a heater matrix or windscreen leak dripping under the dash has corroded the four-relay pack until the fans went intermittent, then dead.
High missing while the lower speeds work, or speeds dropping out one at a time; a clicking relay box.
Open the relay pack and look at each coil's wire ends; each coil should read about 55 ohm. In a blower, bridging the relay's coil feed shows whether the relay or its control is at fault.
Resolder the broken coil wires, or fit a sealed relay. If you replace the in-blower relay, solder a 1N4004 diode across its coil — without it the spike can damage the climate control. The four-relay pack can be replaced by four ordinary relays. The blue relay inside later blowers is worth renewing whenever the board is out.
Cold engine — the heater-pipe temperature switch holds the blowers
In heat mode the blowers stay off until the coolant at the heater is warm — about 104 F on the Mk II. A temperature switch on the heater feed pipe, low on the left of the transmission tunnel, gives the go-ahead. If it fails, the blowers never come on for heat.
From cold, defrost runs but low, auto and high give nothing; everything comes alive once the engine is warm — or never does.
Drive until the gauge is normal and try again. If still dead, unplug the switch and join its two leads: blowers that start now point at the switch, or at no hot water reaching it. If the blowers run on defrost and full cold but not full heat, feel the two heater hoses at the bulkhead: a cold return hose with a hot feed means the heater valve is stuck shut and no hot water reaches the switch.
Nothing, if it's just a cold engine. Otherwise fit a new switch and make sure hot coolant really reaches the heater.
Fuses, fuse holders and the shared feed
The blowers draw a lot of current. Old round fuse holders lose their grip, heat up and melt, and a fuse can look fine while barely passing current. On some years the blower shares a feed with the horn and wipers through a diode that blows if something shorts.
A blower that cuts out or slows on its own; a warm or discoloured fuse holder; blower, horn and wipers all dead together.
Measure 12 V at the blower plug before taking anything out. Feel the fuse holders after a few minutes on high. If the horn and wipers died too, trace the short before replacing the diode or relay — a new one blows straight away. If the lights dip hard each time the blowers start, look for resistance in the heavy feed: clean the two battery posts on the bulkhead and the thick brown cables on them.
Clean and tighten the fuse contacts or replace a melted holder. Find and fix any short before restoring the feed.
Selector switches, loose plugs and earths behind the console
The mode selector works the fans through four micro switches and a vacuum valve on a cam. If the assembly isn't seated exactly, a switch barely touches the cam, and their plugs and common earth point loosen with age.
The blower comes and goes, starts late, or works on some positions and not others, while the flaps and servos can still be heard moving.
At the speed relay by the left of the transmission tunnel, bridge the brown feed to the speed terminal: if the blower runs, the selector side is at fault. Move the wiring in the footwell with the blower switched on. On Delanair III cars where both blowers cut out together, clean the small plugs around the heater unit and the two main earths on the dash braces either side of it.
Reseat the selector assembly exactly — it can take a few tries while cycling every position. Tighten its screws, refit loose plugs and clean the earth for the switches.
The A/C amplifier on Mk II cars
On the Mk II system the resin-potted amplifier, C45402, decides blower speed and compressor, and it fails more than anything else in the system. A failed one makes the controls unpredictable.
Blower and compressor only on defrost, or controls behaving at random, with good relays and selector.
Prove the relays, servos and selector first by bypassing the amplifier; only then suspect it.
Fit a known-good amplifier. Used units are often faulty too and can't be tested before buying, so expect to try more than one.
A blocked air intake or a duct off — the blowers run but little air arrives
Both blowers draw through intakes under the wiper grille and push through soft ducts behind the dash. Masking left after paintwork, a rag sucked into a blower, or a vinyl duct that has slipped off its metal neck starves the vents while the blowers sound fine.
Weak airflow on every speed with both blowers audible, often after bodywork or work under the dash; one footwell or vent stays cold while the others blow.
Lift the wiper grille and look at both intakes. Under the dash, follow the blue ducts from the heater unit and make sure each is on its metal outlet.
Remove whatever is blocking the intake, or push the duct back on and secure it; on one car refitting the ducts under the driver's dash cured cold feet.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Test it warm, and each side on its own
Engine warm, then every position from low to defrost. Pull one blower fuse, try the other side, then swap. A dead blower lets the good one blow backwards into it, so weak air everywhere can be one side only.
freeTap the blower box
A firm knock on the housing frees a stuck motor or shifts debris. If that starts it, the motor or its shaft needs attention.
freeCheck the feed and the fuse holders
12 V at the blower plug with the switch on, and fuse holders that are tight and not hot or melted.
a multimeterProve the control side
On later cars, 5 V to the pink wire at the blower plug should run it near high — never 12 V. On Mk II cars, bridge the feed at the speed relay; a running blower clears the motor and points at the selector or amplifier.
a 5 V supply or a jumper wireRemove the blower and rebuild its board
Undo the housing bolts and hold the bottom flap open so the blower drops free. Renew the Darlington and diodes, clean the motor and oil the bushes before refitting.
a few pounds of parts and an afternoonRelay pack and amplifier on Mk II cars
Open the four-relay pack and check the coils; then the selector micro switches; the amplifier last.
relays a few pounds; an amplifier moreThe fuses named above — where they sit
The highlighted position is the one the procedure talks about. Pulling a fuse is a stop-gap, never a repair: check what the circuit feeds before you pull it.
Circuit descriptions from the Jaguar fuse tables, 1994 edition. Drawing by jagaux.com from the factory electrical guide. Fuse layouts change between model years — read the legend on the lid of your own box before pulling anything.
Circuit descriptions from the Jaguar fuse tables, 1994 edition. Drawing by jagaux.com from the factory electrical guide. Fuse layouts change between model years — read the legend on the lid of your own box before pulling anything.
What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJS Heater Not WorkingIf the fan blows but the air stays cold.
- Jaguar XJS Air Conditioning ProblemsIf the blowers run but the air isn't cold.
- Jaguar XJS Battery DrainIf the battery goes flat overnight — a blower that runs on is one cause.
- XJS fuse boxes and relaysFor the blower fuses on each side, by year.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.