Heated Seats FAQ



Maintained by Nick Blenkush (nixter@emerald.oz.net).


This FAQ is focused on the Saab heated seats. The seats, while acting as a welcome addition on a cold morning, are equipped with small, relatively fragile heating wires which can break over time. This FAQ is designed to inform and enlighten the reader as to possible fixes to the Saab heated seats.

Your input is welcome. Please direct any comments/inputs/criticisms to my e-mail address (autoparts@seanet.com).

Index

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Introduction:

General information on heated seats:

Troubleshooting the heated seats:

Care and feeding of the heated seats:

Posting summaries from the Saab Network:

Introduction

The content of this FAQ is combined from postings to the Saab Network. Please be aware that these are not necessarily facts, just a lot of opinions. What may work for some may not work for others.

If you see something here that you wrote but is not quoted correctly, or if you wish not to be identified, then please e-mail me (Nick Blenkush - autoparts@seanet.com) and it will be corrected.

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General information on heated seats

Heated seats are quite a luxury item to have. The heat helps relieve poor circulation on long drives and makes a cold winter day much more bearable. Although they are relatively reliable and maintenance free, they ARE electrical items which can wear out.

In the lower seat and the seatback is a continuous loop of nichrome wire which serves as the heating element. Since the seats are constantly flexing over their lifespan, the wires can (and often do) break. Much like the Christmas lights of old where one burned out bulb killed the whole string, one break ANYWHERE in the system will cause the seat heater to stop conducting electricity and thus, to stop heating.

In tracking down the possible cause for a non-functioning seat heater, the thing to keep in mind is, "Keep it simple":

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Troubleshooting

If the seats still do not work correctly after checking the basic system out, it's time to look deeper into the system. The following is a breakdown of methods I've heard of and/or used to find and fix the various problems in Saab heated seats:

    2) Slide the seat as far back or forward as it will go to allow easy access to the connector under the seat.

    3) Unplug the seat and verify (with the ignition key in the "on" position) that there is power at the plug. If so, the problem can be assumed to be in the seat itself and not in the electrical power delivery. If there is no power and you have a newer Saab with a heated seat control switch on the dash, the switch is suspect. In some rare cases, the wiring itself may have a break.

    4) With the seat now unplugged, locate and pull out the little plastic plug that connects the seatback to the lower cushion area. With a continuity tester or volt-ohm meter, verify continuity in the seatback. If there is continuity, the problem is most likely in the seat bottom. To verify this, reconnect the seatback to the lower portion (this is IMPORTANT to maintain continuity in the circuit).

    5) Under the seat is the receptacle for the vehicle wiring harness with three pins. Check the continuity between all three (it may be easier to remove the seat at this point, especially if the heating elements will have to be repaired or replaced later). One of the three combinations should give you continuity. Since your diagnosis has taken you to this point, there will most likely be no continuity you've pinpointed the location of the problem to the seat bottom. This is the most comon area for the seat to fail. Owners of Saabs without seat heater controls (i.e., thermostatically controlled) may have a problem with either a broken heating element or bad thermostat (mounted in the cushion). Usually, the heating wire will break right at the thermostat in these cases.

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Care and feeding of your heated seats

Saab heated seats are quite reliable and trouble free but can fail if abused. The heating element in the seat pads and backrest is comprised of a nichrome wire approximately .025" in diameter. While a sturdy material, the wires can break if subject to any excessive and constant force. The main thing to remember is to keep sharp, concentrated pressure away from the seats at all times. Some examples would be:

Remember to keep sharp, heavy objects off the seat cushions; this applies to the seatbacks as well. Always be aware of what you put on the seats. Seatcovers will help some but will not prevent the pressure from transmitting through to the wires. With the proper care, the heated seat can be made to last much longer before the eventual repair is needed.

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Postings from The Saab Network


From Jeffrey C Honig <jch@risci.TN.CORNELL.EDU>

The thermostat in the seat heater I retrofitted to my 1981 900 is the bump under my butt, actually, more like my right leg. About the size of a camera battery. I don't know if an 85 has the temperature control on the dash and if will effect the location of the thermostat.

The heater is usually only noticable when the car is cold (below 40F or something like that). If you are not sitting in the car and let it warm up before you drive away you won't notice it. The heat output is quite noticable to me.


From Bill Randle <billr%saab.cna.tek.com@RELAY.CS.NET>

1) How to tell if your seat heater works: a) find the connector that leads to the seat heater (look around under the seat - it hould be pretty obvious. b) on a cold day (<40 degF inside the car) disconnect the heater connection and connect an ohm meter across it. It should read a small number of ohms indicating the thermostat is closed and the heater wires are good. c) if the continuity is good, but you still think the heater is not working connect a voltmeter to the supply side of the heater connector. It should read 12-14 volts when the ignition is turned on. If it doesn't, check for the obvious things like fuses, etc.

2) How to repair your seat heater: (I did this on my '74 99; the procedure should be similar for later models) a) remove the car seat from the car and take it in to a warmer place to work (this always happens in the dead of winter, right?) b) remove the clips (under the seat) that hold the upholstery in place c) carefully remove the seat cover as best you can d) under the seat covering there will be another this layer of fabric, under which is the heating pad. Look carefully for any burned spots. The most likely spot is near the thermostat. e) [on my seat it was easy to find the break - there was a black spot near the thermostat (in the middle of the pad) where the wire had arced before it completely went] f) clean the end(s) of the broken wire(s) and resolder using a low power soldering iron. You can usually pull up a little slack on the existing wire rather than having to use a new piece of wire. g) reassemble seat cover and reinstall the seat in the car.

The seat heater when its working should be very noticable, especially in colder weather. As Scott said, the wires are notorious for breaking.


From jack%rml@lll-winken.llnl.gov (Jack Hagerty)

Yes, the seat heaters *do* put out a significant amount of heat, there's absoultely no doubt when they're working. It's a case of "if you have to ask, they're not on."

The seat heaters have been a source of major frustration for me. Have you ever had one feature of a car, even a tiny one, reach out and grab your attention? That's the way seat heaters were with me. When I started reading car mags in the early '70s, Saabs were mentioned infrequently and when they were it was usually about some advanced feature like ergonomic controls or crumple-zone/rigid cage construction. But the thing that really made me sit up and take notice in the mid '70s was the introduction of the seat heater (drivers' side only). Why did this strike such a resonant chord in me? Maybe because at the time I was suffering through my fourth winter with my drafty Sprite (you know, the kind with the bake-your-right-knee, freeze-the-rest heater) and the idea of a car that heats up the seat for you before the regular heater fills the car (and not just the footwells) with warmth was immensely appealing.

In any case, I kept an eye on Saabs and by the early '80s when it came time to replace my wife's Fiat, Saab was at the top of the list and stayed there. The only other car really considered was Peugeot, mainly because it also had this most civilized feature.

We took delivery of our 900 in early March '84, still plenty of time to experience the delights of toasted buns (as C/D often put it). Can you imagine my dismay when they didn't work? The seat heaters, I mean. Well, actually they did, a ittle, but not up to spec. The way they're *supposed* to work is to switch on at 50 F or below then switch off again at 80 F. Ours were switching on OK, but switching off again almost immeadiately. I verified this in a quatitative way with an accurate thermometer and a couple of bags of newspapers for thermal mass.

I brought it back to the dealer three times for this seemingly trival problem but the offical Saab test was to spray the thermostat with freon to chill it down and verify that it comes on which, of course, it did. Unfortunately, there was no test to see that it stayed on, so the dealer played a game of specsmanship with me saying that it passed the official test then moaning about all of the time he'd spent checking out a system that was officially "working." To avoid making things any messier (i.e. taking him to court) I struck a deal: in exchage for two dash switches of the type used for the emergency flashers I'd call the deal square and wire the seat heaters manually. I noticed that the heaters in the Peugeot and later in the Merkur and now even in the 9000 are manually operated.

To answer the question in the original posting, the thermostat is located near the back edge of the seat cushion. It's about the size of a nickle but about three times as thick. If the car is an '85 then there should be a circular wear pattern around it by now. Even if not, it's quite easy to find by just ubbing your hand over the upholstery. There is a second heating element in the lower seatback, too, but no thermostat. Additionally, the passengers' seat has a load sensor so that the heater won't come on if no one is sitting in it (a secondary reason for the bags of newspapers in my test). A quick way to check operation is to short out the two thermostat wires and see if the pads warm up. As Scott mentioned, they do have a history of failure after being subjected to concentrated loads (like a knee) or just after a few hundred thousand normal rear end thuds and twists.

Sorry this went on so long, but I've been wanting to write this up for years and send it to the Saab Club. This is probably a better forum, anyway.

- Jack


From CSERVE"76366,23" (Larry West)

The seat heaters and mirror defrosters are different circuits. The only possible common point would be one of the ground points in the car. Does the rear window still defog? Larry Larry West 76366.23@@compuserve.com


From tom coradeschi <+> tcora@pica.army.mil

I suspect that the (nichrome?) heating wires in the seat itself have failed. This would most likely be due to the constant bending they're subjected to. I've never taken the seats in mine apart, so I can't comment on repair (feasibility or method).


From 71151.1354@CompuServe.COM

The problem with heated seats on some 900s is that a fix seems to be temporary. My understanding is that when Saab switched to the rheostat controlled seats in 1988, that they became more reliable. The problem with the heating elements is that the wire grids seem to be fragile, and the thermostats keep coming loose or blowing out. They can be fixed easily enough if you want to go to the trouble of removing the upholstery from the seat cushions. Use a multi-meter or continuity tester of some sort to locate the break, solder in a wire patch and hope it stays working for awhile. You might consider replacing the thermostat with a rheostat, but don't put in an ON-OFF switch as a fire could develop if the heater is wired direct to full power.

Tim Winker Saab Club of North America


From dxn@oclc.org

I wanted to let everyone know how I faired with my non-functional heated seats last week. The car is an '86 900 (base).

The key to this whole exercise is to be able to determine whether the circuits involved are continuous or not. It seems to me that a good VOM is essential.

-Check the fuse first!

-Next thing to do is remove the seats (two fasteners for drivers seat and four for the passenger seat).

DRIVERS SEAT: -Check for voltage from the connector sticking out of the carpeting. Make sure the ignition is "ON".

-Slide back the bottom seat cover. On my car, there are 4 or 5 upholstery clips on the front-bottom edge of the seat. There is also a metal rod along the inboard edge of the seat which needs to be popped out. Take out the thermo-switch located in lower-right quadrant of seat under an access slit (see pic):

and check it. The switch should have continuity when it gets cold enough. (I put mine in the refrigerator. The Bentley manual says you can also use a commercial freeze aerosol to check the switch while it's in the seat.)

-Before replacing the thermo-switch, jumper the two loose wires so that you have a complete circuit for the seat heater. Check the continuity of this circuit at the connector under the seat bottom. If it's not continuous then you have a break in one of the heating elements or in the wiring which connects to the heating elements.

The heating element break point probably has a blackened area around it. Don't forget that the lumbar area of the seat also has heating elements. Unzip the seat back from the bottom and pull up on the cloth.

If you do have continuity, then plug the seat in and try it out! The heating elements get very warm under the seat upholstery and there should be no doubt when they are working.

-Reassemble the seat with the working thermo-switch in place.

PASSENGER SEAT -Same as drivers seat, but with a "load-sensing" switch in the circuit. There are two connectors for the passenger seat: one is a power supply and the other gets "input" from the "load-sensing" switch on the seat bottom. (This "load" switch is a simple affair involving a spring, chain, housing, and two wires.)

-Jumper the connector (that sticks up through the carpet) which connects to the "load-sensing" switch and check for voltage at the power supply connector. Again, make sure to have ignition ON for voltage test.

-Check the "load-sensing" switch. Connect the VOM probes to the "load-sensing" connector on the seat bottom. Sit on the seat to check for continuity.

-Check the thermo-switch in the same way as the drivers seat.

My seat-heaters didn't work because the driver's seat thermo-switch was bad (always continuous, but discontinuous with power applied), and the passenger-side didn't work because the "load-sensing" switch was bad (someone munged one of the wires in the spring-loaded section of the switch and the wire eventually broke).

A new thermo-switch costs about $20 from the dealer. About the same price for the "load-sensing" switch (oddly, the switch for the '87 900 has a larger connector, shorter chain and costs twice as much!?).


From gmh@hpfcgmh.fc.hp.com

The heating pad itself seems to be a common failure component. I just replaced both pads in my '85 900T and have toasty buns again.

You can measure the resistance through the pad, to check for an open. This would have to be done when the pad is below the thermostat close temperature on my 900 without the dash control. I'm guess you still have a thermostat in the pad even with your dash switch.

I have the Bentley manual, wihch has a reasonable wiring diagram.

The job itself was about 2 hours for the first seat, an hour for the second when removed from the car.

Greg Hughes gmh@fc.hp.com


From nblnkush@prostar.com

The little heater wires in the seat tend to break due to contact pressure on the seat. If you put your butt in the seat, no problem. But if you kneel on it, throw packages on it, or if a small child stands on it this leads to point pressure on the wires; over time they will break. This is a common problem. The seats cannot take much abuse. You have two options:

1. Go to the dealer and buy a replacement heating pad (~$150) 2. Pull the seat cover off, trace the broken wire, and solder it.

I've had luck using method # 2. It takes time and patience but I figure it's worth $150


From Clark Wilson (100063.2350@compuserve.com)

Yes. Ever since day dot. The seat heaters in Saab's always end up burning out, especially in the old 900 pre rheostat days. Just replace it as there is nothing else you can do about it. Regards.


From george suwala (suwala@bnr.ca)

> Has anyone ever hooked up a switch to bypass the thermostat for the passenger-side heated seats in an 89 SAAB convertible?

I did it in the driver's seat of 1986 9000T, which I believe should be similar to the passenger seat of your 900.

I removed the seat assembly from the car, removed leather from the seat bottom, soldered in bypass wires and placed a bypass switch (toggle type) in a hole drilled in the front of the seat. To activate the heat at any time, you just need to flip the switch to ON, reaching under the seat between your legs. With the switch in OFF position system works as designed by SAAB. You can run wires to a switch in a dash, but I did not bother with this trouble.

Thermostat is visible through the foam on the top the seat (you need to rip the foam to access it).

The whole operation was very easy, except for removal/installation of leather, which needs to have some hooks removed from under the seat (which takes some time to get proficient with). No force should be needed at any time.

A word of WARNING - with thermostat bypassed you run a risk of fire if temperature gets too high and the manual switch is not turned off. Use at your own risk.

Regards

George


From Mike Goldstein (mikeg@ICD.Teradyne.COM)

Sounds like the voltage you are seeing is low. Though I don't claim to know the desired values. Check the ground side...

m.


From Mike Vande Weghe (vandeweg@bbn.com)

I remember looking at the seat wiring diagrams a few months back, and I think I know what your problem is. I believe the way the rheostat system works is that the thermoswitch is mounted in the dashboard assembly, and a temperature sensor is located in the seat. The rheostat controls the threshold of the thermoswitch, which opens and closes accordingly in order to maintain the correct heating level.

In the non-rheostat system, there is a thermoswitch in the seat cushion (instead of just a sensor) with a preset value. It just toggles on and off to maintain the correct heating level.

I believe you now have a hybrid system. You have a rheostat on the dash with the thermoswich, which is expecting to be connected to an external temperature sensor and heating coil. In the seat, however, is a heating coil in series with an additional thermoswitch. You have two thermoswitches in series, and since the dash one is always open (without being properly connected to a sensor) you get no heating all the time.

I think you can fix all of this by shorting out the thermoswitch in the seat, and adding a temperature sensor. This might be most easily achieved by obtaining an entire heating pad assembly from a car that had the rheostat. Whatever you do, be sure to keep some sort of temperature regulator in the system; if the heating pad runs unregulated, it may get hot enough to pose a fire risk.

Mike Vande Weghe


From wombat@netheaven.com

These pesky thermostats are an annoyance. When I repaired my seat heaters I just removed them and put small switches in the side of the seats so that if you want heat in your seat you just flick the switch. A question I have is, despite being smaller, the replacement heaters I nabbed from a junker that had recently had it's seats rebuilt, do not get as hot as the original heaters. I only replaced the bottom pads as the back warmers were still intact in my car. My guess is that the replacements use more insulation or a different conductor that is less prone to breaking. Can anyone give a definitive answer on this?


From D.W. Blackie (D.W.BLACKIE@dundee.ac.uk) -- My 900i exhibited the same symptoms on the drivers seat ( no variable control on this UK model ) so I dismantled it and everything checked out OK. I came to the conclusion that the thermostat must be cutting out at too low a temperature. In order to get a decently hot bum I wired in a switch to by-pass the thermostat. Strangely enough when I put it back together again the heater worked fine without requiring the switch. I assume that the position of the thermostat is critical to when it cuts out and I must have put it back in a slightly different position from where it was originaly. I now have the bonus of being able to switch in some extra heat if want it.

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