740 Dashboard heater vents!

[tofufi]

Hi folks,

As I was doing another 400 mile round trip in the pretty cold weather this week, I noticed that the air coming from the centre vents on the dash was significantly cooler than those on the outside of the dash by the doors. In fact, with the heater set to maximum, closing the air-flow to the centre vents resulted in the car being warmer inside.

It was cold enough that it took 130 miles for the ice on the bonnet to melt...

Is this meant to be, or is there something not quite right in my heater box? I'm wondering if cold air is getting past into the heating system when it shouldn't...

[stephend]

It is meant to be. I know it's strange, but it's as the vehicle handbook shows it: ambient air from the centre vents, hot air from the end vents, footwell vents, and the, er, nether regions warmer (aka b0ll0ck warmer... )

Means that, once you've got going, you can get warm air for general heating from the warm air vents, and fresh air to your face for the purposes of staying awake in the fug!

[tofufi]

Thanks

Sadly, on that trip the nether-regions-warmer on my seat wasn't functioning - I suspect I forgot to connect the wires when I removed the centre console. Gives me something to do today

[stephend]

Ah, now, by nether-regions-warmer, I was actually referring to the sneaky little dashboard vent directly below the steering column, that directs a lovely comforting blast of roasting hot air straight in the direction of... well, you get the idea! Whereas I think you're maybe referring to the heated seats?

Re the vent, two things I've found can go wrong are (1) if the trunking gets detached, or you forget to reattach it after having the trim panel out; and (2) on mine the little flap and wheel thingummyjig sometimes sticks and needs some persuasion to free it up.

Heated seats: good luck with that! On mine, the lights on the switches light up, but no heat is produced at either seat. I'm assuming that either there's a wiring problem, or that the heater pads themselves have failed. I believe they're still available from Volvo, and that it's a DIY job to fit them. They're on the to-do list...

[Laird Scooby]

Some cars have a thermo-switch under the seat to detect "ambient" temperature and the seats don't heat up if ambient is above 10C if memory serves correctly. Trouble is, when the switch under the seats senses "ambient" it's detecting ambient inside the car, not outside!

Can be a real pain in the bum, almost literally! Since having the drivers seat out on my 760, the bum-warmer now only works when it thinks it will, regardless of temperature inside the car. Annoyingly it worked before i removed the seat to fix the electric adjustment...........

[stephend]

Tbh, the 740 isn't my daily driver, and it's got cloth seats, so - how can I put this delicately? - one's backside warms up quickly enough without the need for the heater. Now, my Toyota's got leather seats (as did the V40 before it), and I really wish it had seat warmers, cos first thing on a perishing winter's morning, getting into the car leads to a real "ooh!" moment...!

Time to break out the winter trousers, methinks.

[Joe of Loath]

Originally Posted by stephend

It is meant to be. I know it's strange, but it's as the vehicle handbook shows it: ambient air from the centre vents, hot air from the end vents, footwell vents, and the, er, nether regions warmer (aka b0ll0ck warmer... )

Means that, once you've got going, you can get warm air for general heating from the warm air vents, and fresh air to your face for the purposes of staying awake in the fug!

That's an interesting one, because occasionally warm air comes out of the centre vents on mine, and the end ones blow cool. I'd put it down to dodgy vacuum lines as it only sometimes will switch to foot warming when I tell it to.

[tofufi]

Originally Posted by stephend

Ah, now, by nether-regions-warmer, I was actually referring to the sneaky little dashboard vent directly below the steering column, that directs a lovely comforting blast of roasting hot air straight in the direction of... well, you get the idea! Whereas I think you're maybe referring to the heated seats?

Re the vent, two things I've found can go wrong are (1) if the trunking gets detached, or you forget to reattach it after having the trim panel out; and (2) on mine the little flap and wheel thingummyjig sometimes sticks and needs some persuasion to free it up.

Heated seats: good luck with that! On mine, the lights on the switches light up, but no heat is produced at either seat. I'm assuming that either there's a wiring problem, or that the heater pads themselves have failed. I believe they're still available from Volvo, and that it's a DIY job to fit them. They're on the to-do list...

Ah yes, I forgot about that one It's a pig to re-connect after taking the trim panel off!

Heated seat now fixed, it was just a poor contact at the switch after I had the gear lever surround apart recently

I've got a complete set of working heater pads, switches etc from a 940 which I'm quite tempted to fit to my old (70s) Rover

[stephend]

Originally Posted by Joe of Loath

That's an interesting one, because occasionally warm air comes out of the centre vents on mine, and the end ones blow cool. I'd put it down to dodgy vacuum lines as it only sometimes will switch to foot warming when I tell it to.

Afaik, if your '88 740 is like my '89 740, the heater controls are cable-operated; I'm not sure if vacuum lines come into it on 700s of our vintage...?

I do get a bit of a time-lag between setting the temperature control and it coming into effect on mine. Not sure why, but I've traced the cables to the heater control valve and to the distribution shaft, and they seem to be working correctly. It's a puzzle...

[Laird Scooby]

Originally Posted by Joe of Loath

That's an interesting one, because occasionally warm air comes out of the centre vents on mine, and the end ones blow cool. I'd put it down to dodgy vacuum lines as it only sometimes will switch to foot warming when I tell it to.

Could also be dodgy non-return valves in the vac lines - you know the non-return valve for the brake servo, they're like a small version of that.