Seat heater questions 1994 volvo 850

ironslave · Post by **ironslave** » 29 Mar 2008, 00:58

i was wondering how the seat heaters work? are they wired to the climate control and then heat up until the car is at ambient temperature or are they a simple on/off thing?

Post by **JRL** » 29 Mar 2008, 06:37

They have a (usually bad) thermostat under the seat, otherwise, on-off

Post by **MadeInJapan** » 29 Mar 2008, 07:41

A lot of times it's just a wire to the thermostat that gets chafed from the seat's movement back and forth and thus breaks the connection. Push your seat all the way back so you have room to get under the front of the seat and take a look. If it's a broken wire, that's an easy repair. Otherwise, as JRL mentioned it's the thermostat itself, which you'll have to dig out from under the bottom of the cushion and replace.

Post by **JRL** » 29 Mar 2008, 07:59

The heated pads just die on 850's and it may need to be replaced
So in your check, check everything, the thermostat, the pad itself AND the switch

Post by **Maxbaby** » 29 Mar 2008, 11:12

I'm going to provide this link to Lee's writeup on the drivers seat.

https://www.matthewsvolvosite.com/chat/p ... hp?p=30367

No, you're not interested in replacing foam, but if you read it, you will see the connectors and the heating pad itself. It's not that hard to pull apart in case you determine you need to replace the pad. You can run a continuity test from the electrical connectors for the pads to determine if they have a break in the heating wire.

ironslave · Post by **ironslave** » 29 Mar 2008, 11:42

sometimes the heaters work, some times they dont. is the seat heater in the back and the bottom? i could swear that only the back works but the seat dosent.

Post by **JRL** » 29 Mar 2008, 12:31

ironslave wrote:sometimes the heaters work, some times they dont. is the seat heater in the back and the bottom? i could swear that only the back works but the seat dosent.

Then the bottom pad is disconnected or broken. heat everywhere

Post by **Ozark Lee** » 29 Mar 2008, 14:42

sometimes the heaters work, some times they dont. is the seat heater in the back and the bottom? i could swear that only the back works but the seat dosent.

That really can't happen. The heater pads are in series with each other. If one pad burns out then the other one won't work.

Here is how to check the system out:

Look under the seat, on the right hand side as you look at it from the footwell, and locate the power connector for the seat.
It is the large white connector with the Yellow/Red wire and the Black wires.

Use a Voltmeter and, with the seat heater switch on and the key on, check for battery voltage between the Yellow/Red wires and the Black wires. If it measures good there it means that the switch is good and the wiring to the seat is good.

You next need to locate the heater pad plugs, they are just below the front edge of the seat, they are both 2 conductor connectors. One connector is gray and the other is black.

They are pictured here:

Backprobe the red wire on the black connector and check it for battery voltage as well, the black wires on the power connector are a good ground point for the meter.

If you have good voltage there it means that the thermostat and its circuit are good. If you don't have voltage there it means that the thermostat is bad (not likely) or the wiring to the thermostat has come unplugged (more likely). The thermostat is located near the rear of the bottom seat cushion and it has a Red wire and a Red/White wire going to it. Plugging it back in is tricky and is best accomplished from the back seat and having someone sitting in the seat - that someone will get goosed a bit.

Assuming that the voltage is good on the red wire next move to the yellow wire. On a normally working system you should read voltage there but it will be less than full battery voltage.

If you read full battery voltage on the Yellow wire then the seatback heater element has burned out.

If you read no voltage there then the seat bottom heater element has burned out.

...Lee

ironslave · Post by **ironslave** » 30 Mar 2008, 23:44

thanks for the input, i will look around tomorrow, can anyone give me an estamate as to how long it take for the seat to heat up?

Solutech · Post by **Solutech** » 31 Mar 2008, 04:27

Mines starts to heat in about 20 seconds or so . Gets to full heat after a couple of minutes .