P38 HEVAC Blend Motors:
Diagnosis and Replacement



Blend Motors? What are they??
Symptoms and Diagnosis
Official Procedures for Accessing the Blend Motors
Overview of Short-Cuts
Accessing the Right Hand Blend Motors
Accessing the Left Hand Blend Motors
Reassembly and Rewiring
Tips from Other Owners
Replacement Parts Availability



Blend Motors? What are they??
Among the most talked-about and cursed-about parts on the P38 Range Rover are the HEVAC (HEating, Ventilation and Air Conditioning) blend motors. What exactly are they?? Well, they are electric motors (actually servos) which control the internal vent flap positions in the HEVAC system to direct hot or cold air where it is wanted. In the old days these flaps were controlled by mechanical levers, but thanks to the march of technological progress, they are now (at least on high-end cars like Range Rovers) moved electrically under computer control, thus providing many more components that are likely to fail. In the official workshop manual, they are called various names including "blend flap servos". There are actually 5 such servo motors altogether (see below), but the 3 that are attached to the central heater unit are the usual culprits. To slightly simplify their roles, two of these (known as the temperature or blend motors) control the flow of hot and cold air to the left or right depending on driver and passenger temperature selection, and one (the distribution servo) controls the relative distribution of airflow to the footwell, fascia vents and demister vents. Each servo looks like a rectangular box about the size of a packet of cigarettes, attached to the sides of the heater box which is buried under the dash. Failure of these motors is unfortunately common. (Drawing at top right, adapted from the shop manual, shows the temperature and distribution servo located on the right side of the heater body, just above the heater core O-rings. Photos below show what a blend motor looks like and where it fits).

Ron Beckett has once again come through with amazing insights on this problem, which when combined with the input from other owners  should make the repair procedure less of a headache for future Range Rover owners. Ron and I are particularly grateful to David Sparkes who pioneered the search for shortcuts on this tedious procedure.

Symptoms and Diagnosis
A stuck blend motor will usually cause the book symbol and exclamation mark to be displayed on the HEVAC LCD panel. However, to narrow down the cause of the fault message, the following diagnostics may help.  The symptoms listed below can all indicate blend flap servo motor failure, but before tearing into the dash, check for blown HEVAC fuses (8 and 17) which can also cause all these symptoms. Also, if the system will not emit any hot air at all, the problem may also be due to blocked heater hoses.

1. Heater emits cold air only only or or hot air only to driver or passenger sides: The left or right temperature vent flaps may be stuck in closed or open position due to failed servo motors. These servos, known as the temperature or blend servos, govern the blends of hot and cold air sent to the driver and passenger sides depending on their different whims, and are each mounted in a horizontal orientation on the left and right sides of the main heater housing at the center of the console.
2. Hot or cold air emitted to demister only, fascia only, fascia and footwell only, or footwell only. This can indicate the heater distribution vent flap is stuck in the demist, fascia, fascia/footwell, or footwell positions due to a failed distribution servo motor. This motor is mounted in a vertical orientation on the right hand side of the central heater unit just above the RH temperature vent flap servo. (Note that this servo is mis-identified in the official drawing number 82M-0572 in the shop manual, where the labels for the right hand temperature blend motor and the distribution motor are interchanged). You can test its operation by trying the different settings on the bottom row of buttons on the HEVAC control panel which control the air distribution, and seeing if the air comes out where it should in each setting.

3. Heater emits recirculated or ambient air only: This can indicate an air inlet housing vent flap is locked in the closed (recirculate) or open (ambient) position due to servo motor failure. These motors are referred to in the shop manual as the left and right recirculation flap servos, and are mounted peripherally on the blower motors located behind the pollen filters and forward of the extreme left and right fascia vents.

Photo at right: Blower motor at extreme left of dash (photo taken by Ron Beckett in a partially dismantled vehicle). Left recirculation flap is mounted on this motor but not visible in this photo.

The two servos in item 1 above, and the single servo in item 2 above, are the three items usually referred to as the notorious "blend motors" and sold as official parts in a set of three. It is the replacement of these three motors that the remainder of this page is devoted to. However, note that the other two servos mentioned in item 3 above, although less publicized, can cause trouble too. Occasionally the blend flaps themselves, rather than the motors, can be the culprit, necessitating a whole new heater box. However this is unusual -- normally it is just the servo motors at fault.

Root causes of these failures include lack of attention to regular replacement of the pollen filters -- see the pollen filter replacement page.

Official Procedures for Accessing the Blend Motors
On vehicles without air conditioning, accessing the blend motors is relatively simple, and well covered in the shop manual. It merely involves dropping the glove box or the lower fascia panel under the steering wheel (depending on which side you want to access) and removing the center console side trim panels, giving access to each side of the heater box where the blend motors are mounted. Removing the radio, HEVAC control pack and fascia switch pack is also recommended to give good access to the front of the heater unit, mainly to remove and replace the blend motor wiring harness or parts thereof.

On vehicles with A/C (unfortunately the vast majority of Range Rovers), after removing the relevant side panel and either the glove box or lower fascia panel, you will find that each side of the heater box where the blend motors are mounted is obscured by a wide, flat air duct which travels down each side of the heater box on its way to supply (ineffectively) air to the so-called rear face vents. For these models, the official procedure (outlined in the shop manual) is to remove the entire fascia (see the dash removal page) and take out the heater box entirely. This allows you to unscrew the two screws holding each heater duct on to the side of the heater box, exposing the blend motors for easy removal. The charge for all this at the dealer is usually about 12 hours of labor (quite reasonable actually!) plus about $200 for the parts.  This official procedure also involves disconnecting the coolant hoses, so if you do it the official way you might as well replace the heater core "O" rings in the process (see separate page).

Overview of Short-Cut Access Methods
Because the official procedure involves so much dismantling, shortcuts have been developed by resourceful mechanics, and experienced repair shops can usually do it for 6 hours of labor. This is particularly true if only one of the blend motors is replaced (even though they are sold in sets of three, the shop manual gives procedures for splicing each one separately into the wiring harness). For this reason it is handy to know in advance which blend motor is malfunctioning (see diagnostic procedure above).  Naturally the  necessary procedures vary slightly on left and right hand drive models, since you need access to a particular side of the heater box depending on which blend motor has failed.

All the shortcut procedures basically involve following the official instructions intended for models without air conditioning, then fighting your way through to the blend motor mounting screws by drilling, pulling aside, mangling or otherwise conquering the ducting covering the side of the heater box. If you are worried about damaging this duct during the operation, remember that even its complete annihilation would hardly be noticed, as the rear face vents are so ineffective anyway. I recommend being ruthless with this near-useless bit of plastic and then just patch it up again with duct tape when you are done. For example, on his RHD model, Bob Franklin ended up cutting the ducting in front of the motors completely in half as it made it so much easier, and then just duct taped them back together. It worked perfectly.

The following procedure and photos kindly contributed by Ron Beckett illustrate a kinder and gentler approach that does not involve damaging the duct in any way, and it is followed by additional insights from other owners who have performed this operation.

Note: An alternative procedure to that outlined below is to remove the dash/fascia -- Jos Geuze reports that this provides good access to the blend motors without doing the rest of the official procedure. For details, see the dash removal page.

Right Hand Temperature Blend Motor and Air Distribution Servo Access
As mentioned above, the blend motors are located on the side and above the transmission hump - actually just above the footwell air vents. Access methods have much in common with accessing the heater core O-ring seals. To get access to the right hand temperature blend motor you will have to remove the glove compartment (LHD vehicles) or the lower fascia panel under the steering column (RHD vehicles). You also have to remove the right hand side panel (for the latter see the page on Removal and Replacement of the Side Panels. With the side cover off, you now have access to the lower air vent and duct. The outer vent outlet just pulls off. The inner vent outlet is retained by two screws, one of which also holds the air duct in place. Remove these two screws (see photos below).
  

The rear face vent duct which runs from the screen down the side of the heater to the floor is now blocking your view of the blend motors. This duct is further retained by a second screw hidden behind an inner panel. You have two options: (a) pull on the duct to break off the mounting lug or (b) drill a hole through the inner panel to access the screw. This hole will be covered when you refit the side finishing panel removed earlier. The photo below shows where to drill the hole to access the hidden screw. 

At this point, the access procedures diverge for the LHD and RHD vehicles - but this section deals with the additional access for RHD vehicles. In this case we need release the top of the duct to allow it pivot out of the way at the bottom. This will become clear when you do the job. On RHD vehicles, to do this we have to remove the instrument panel. It may not be strictly necessary to do this but Ron didn't feel comfortable with flexing the lower heater duct out of the way to get to the O-ring heater connection screw. So for RHD vehicle owners, we refer you to the separate page on Removal and Replacement of Instrument Panel.  After this operation, you will now be able to access the top of the heater ducts. These connect the heater to the upper outer dash vents and to the floor vents. Our goal is to release the top end of the rear face vent duct which is attached to these upper ducts. 

Referring to the pictures below, slide the intermediate joiner to the right to disconnect the inner duct from the outer duct. This will allow the inner duct to be separated from the heater and swung away at the lower end near the heater matrix. It will require quite some flexing of the duct to get it out of the way - but it can take it the flexing.

You should now be able to access the right hand blend motors. The temperature blend motor is the lower one, oriented horizontally, and the distribution motor is mounted in a vertical orientation just above it. Each motor is held in place by two diagonally opposite screws.

For details on replacement, see the Reassembly and Rewiring section below.


Left Hand Temperature Blend Motor Access
On the left side of the heater box there is only one blend motor, the LH temperature blend servo. This is mounted in a horizontal orientation just above the left footwell vent, in a position which corresponds to that of the RH temp blend motor pictured at the top of this page.

On RHD models, access to this motor is easiest and simply involves removal of the glovebox and left hand side panel. Then the procedure outlined above can be used to detach the top of the duct serving the rear face vents so you can remove it and see the servo.

On LHD models, this motor is the easiest to access. You just should remove the lower fascia panel under the steering column, and the instrument binnacle (see Instrument Binnacle Removal and Replacement page). Then follow the same procedure as above.

Reassembly and Rewiring
Ron has looked into the feasibility of rebuilding the failed blend motors. However he has found that the two wear areas (from his dismantling efforts) are the feedback pot which we cannot source, and the brushes on the motor. One could replace the brushes (by making new ones if necessary) and clean up the armature and the muck in the motor, but it's probably a short term (a year or so) fix. Considering the amount of trouble it is to access the motors, you are far better off to buy new ones. See the parts availability section below.

The main issue to be addressed on reassembly is how to handle the wiring of the new blend motor. The official procedure involves disconnecting the leads for the blend motor being replaced from the connector which is common to all three motors. The connector is located behind the HEVAC control panel, and access to the wiring loom requires removal of the radio and the fascia switch panel. These are not too hard to remove, and if you are replacing all three blend motors this is the way to go. However if you are only replacing the failed one and are trying to minimize time spent (knowing that SWMBO is threatening to sell your Range Rover on EBay if you spend any more time underneath it), you might prefer to bypass this step and just cut off the wires to the old servo when you remove it, and splice in the new ones using either crimp connectors or solder. 

Any other issues re the wiring harness problems? Any other tricks?

When reconnecting the battery, if you have disconnected it eg to remove the SRS, don't forget to reset all the windows and the radio code.

Tips from Other Owners
David Sparkes was the pioneer in this effort to find ways of changing the blend motors without disassembling the entire vehicle. He relates his experiences with this job on his RHD model on Andy Cunningham's excellent page at this link. David notes that you can remove the two screws that fasten the offending air duct to the sides of the heater box, allowing you to detach it from the rearward ducting at its bottom end and pivot it about the point where it attaches to the main output duct at the top. This gives at least partial access to the two underlying screws holding the blend motors in place. The lower one is easy to access, but the top one is still obscured. Unfortunately the screw holding the top of the offending air duct to the main duct is not accessible, so you can cut or drill holes in the plastic framework where needed to get through to the remaining blend motor screw (as suggested by Ron Beckett -- see photo above).

Kanaka, with help from his brother, managed to replace all the blend motors on his North American spec RR without removing the fascia panel. First he removed the glove box, console side trim panels, the lower fascia panel under the steering wheel, the speedometer trim, passenger side air-bag, radio, heater control panel, and fascia switch pack (headlights, fog lights, EAS selector). He disconnected the above-mentioned air duct which supplies air to the rear, and drilled through it to get access to the blend motor mounting  screws. He used a specially fabricated screwdriver to access the more awkward ones. The whole job took 9 hours, and the dreaded textbook symbol was gone.

Reflecting on the problem of getting past the heater duct, I have been wondering if something hot like a soldering iron might come in handy for cutting away the offending sections where there is not enough room to get in with a pair of tin snips. If you try a soldering iron, be careful about the fumes that might be created.

Replacement Parts Availability
New and Used Genuine Parts:
The official replacement part needed for this repair is the blend motor kit containing three motors mounted together with one plug. The part number is STC3259, which fits all model years 1995-02. I recently found them for $199 at British Pacific and for $182 at Atlantic British. The kits occasionally show up used on Ebay, but it is hard to be certain about their reliability especially considering the work required to change them.

Note the blend motor for the fresh air/recirc flaps (mounted to the blower motors behind the extreme left and right fascia vents -- not covered in the above disassembly operation) is a separate part number, STC3266. This is available from Atlantic British for about $109. You may also be able to use this part for replacement of any single motor on the heater body and splice in the wire connections.

Substitute Parts from Other Vehicles:
Although no official aftermarket substitute is available, alert Range Rover owners have recently noticed that the blend motors are the same as used in certain Peugot models including the 405 and 406. Even the wiring loom is the same with the same colored wires. The Peugeot part number is P644758. Ron Beckett pulled the blend motor out of his daughter's 1989 Peugeot 405 as it had stripped some gears, and noticed that it was almost identical to the servo used in the P38A. He was able to repair it using the two gears from the old Rangie servos he had replaced the previous year (they were same tooth pattern and number of teeth but were more substantial in the thickness of the gear wheel). The only electrical difference Ron found on the Peugot was that its servo (5 years older than the Rangie's) had inductive suppressors rather than capacitors. It is quite possible that later replacement parts are different to the old '89 part and match the P38A Rangie part. 

More Information:
See Climate Control section of the P38 Aftermarket and Generic Parts page for more information on parts availability.