REST Function

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W210Virgin

Active Member
Joined
Feb 25, 2014
Messages
255
Location
Norn Iron
Car
2002 S210 Avantgarde 320CDi in silver. Black leather interior
My REST function seems to operate properly in terms of fan action etc internally but recently I noticed that the air blowing was cold or near cold. A quick check of the pump, mounted on the front chassis leg area near the expansion tank, and it wasn't running. A quick check of this and there's no voltage at the pump, assuming it should be showing 12V as normal. I should also mention, given that I don't think I've used this function before, it is likely that it has not worked in my ownership, about 13 months now.

Now I'm a bit stumped. What to check next and is there a separate fuse for the pump?

Car S210 320CDi 2002
 
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I think that is the auxiliary heater (that fails on every car), not sure if it's also used for the rest function. Someone can hopefully confirm
 
My understanding is that Rest and Aux Heater are separate functions. My car has rest but not Aux heater.
 
REST function only operates with the IGN off. It utilises residual heat from the engine coolant to warm the cabin. Coolant is circulated by a small electric pump. Air distribution flaps and blower settings are non-adjustable. 30min max operating time or until battery voltage drops below a set value. Works really well with one exception, the incoming warm air isn't dehumidified so windows miss up very quickly!

The electric pump only runs with the IGN off, so if you checked with the key in any position other than '0' you'll shouldn't see a voltage at the pump.

Aux heater can be an electric heater element within the a/c heater housing or a separate fuel powered burner mounted in the off-side wing, the latter is more correctly termed Stationary Heater
 
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Thanks Whitenemesis. Useful info. Not totally sure where my ignition position was when I checked for voltage so I'll double check that. If I've no volts and everything else is running OK, where can I check? Where is the wiring of the pump fed from?

My stationary heater, switched from the ashtray location, doesn't seem to work either. Is is really in the O/S wing? I had both wheel arch liners out over the Christmas holidays checking for rust and other than the alarm siren don't remember anything else in there. Is it by any chance in the N/S arch towards the front as I have a recollection of something in there? This might seem more logical too as the fuel lines run up that side and the filter etc is on the N/S?
 
Thanks Whitenemesis. Useful info. Not totally sure where my ignition position was when I checked for voltage so I'll double check that. If I've no volts and everything else is running OK, where can I check? Where is the wiring of the pump fed from?

My stationary heater, switched from the ashtray location, doesn't seem to work either. Is is really in the O/S wing? I had both wheel arch liners out over the Christmas holidays checking for rust and other than the alarm siren don't remember anything else in there. Is it by any chance in the N/S arch towards the front as I have a recollection of something in there? This might seem more logical too as the fuel lines run up that side and the filter etc is on the N/S?

The aux heater is under the vacuum tank on the left of the engine bay...they don't usually work...you will not have the stationary heater under the o/s wing.

REST only works with the engine off.
 
The aux heater is under the vacuum tank on the left of the engine bay...they don't usually work...you will not have the stationary heater under the o/s wing.

REST only works with the engine off.

Can't see aux heater at all; only the Rest pump/ heater/ reservoir (with a connection from the alternator on it??). Assuming, of course, left is as viewed from front of car. As for the other side hard to see much with the power steering reservoir and wind screen washer/ ABS stuff in the way.

While we're off topic, and I'm pretty sure my aux heater doesn't work anyway, but as it burns diesel will it not be 'outside' the engine bay with an exhaust of sorts from it?
 
If you do have the stationary heater (Webasto?) it will be under the front wing, forward of the front wheel.

SA code 228 on the datacard IIRC
 
Can't see aux heater at all; only the Rest pump/ heater/ reservoir (with a connection from the alternator on it??). Assuming, of course, left is as viewed from front of car. As for the other side hard to see much with the power steering reservoir and wind screen washer/ ABS stuff in the way.

While we're off topic, and I'm pretty sure my aux heater doesn't work anyway, but as it burns diesel will it not be 'outside' the engine bay with an exhaust of sorts from it?

You are in the right area...what you see is the aux heater...there is no separate REST heater. You don't have the diesel powered heater...just the one directly from the alternator...and switched on in the ashtray. But (when it works, which it wont) it only operates below 7oC.
 
Definitely have "a" heater as the switch is in the ashtray and the manual describes it's use and burning diesel etc. Pretty sure it doesn't work though. Makes sense as a location as there's A/C stuff in there too.

I'll check Rest function again when I get home and the car is nice and hot and report back. With and without ign.
 
Definitely have "a" heater as the switch is in the ashtray and the manual describes it's use and burning diesel etc. Pretty sure it doesn't work though. Makes sense as a location as there's A/C stuff in there too.

I'll check Rest function again when I get home and the car is nice and hot and report back. With and without ign.

You only have a switch in the ashtray...not a timer unit which is associated with the diesel powered one.
 
You are in the right area...what you see is the aux heater...there is no separate REST heater. You don't have the diesel powered heater...just the one directly from the alternator...and switched on in the ashtray. But (when it works, which it wont) it only operates below 7oC.

Cool. Very helpful thanks and that makes sense and getting closer. I was wondering why that alternator feed was in there but I had my suspicions. When they go wrong, what is the fault? Is it fixable?

And, as the alternator feed is in there, where does it eventually connect to the battery?
 
Definitely have "a" heater as the switch is in the ashtray and the manual describes it's use and burning diesel etc. Pretty sure it doesn't work though. Makes sense as a location as there's A/C stuff in there too.

I'll check Rest function again when I get home and the car is nice and hot and report back. With and without ign.

You may have the button but maybe someone removed the heater.
 
Thanks but as Renault21 noted above, it doesn't have a timer and therefore it is an electric version, hence the feed from the alternator. However, it looks like it doesn't work or the pump. I'll need to check again properly tomorrow as I didn't get doing it this evening when there was enough heat in the engine.
 
The Aux heater has nothing to do with the REST function.

The Aux operates once the engine is running, taking any surplus current from the alternator to boost the coolant temperature. Circulation is dealt with by the engine water pump.
The REST only operates with the IGN off and the coolant is then circulated using the electric pump.
 
Sorry didn't mean to preach...
 
Perfectly OK. No apology required. Appreciate the input.
 

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