Xantia HDi Water Coolant Heater

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Rhothgar
Donor 2023
Posts: 1733
Joined: 22 Nov 2004, 01:21
x 77

Xantia HDi Water Coolant Heater

Post by Rhothgar »

Afternoon,

Progressing steadily through fault codes on the Xantia and one I've left until last is the wonderful Water Coolant Heater block which tried to set on fire last year.

So...

the question today is how does it actually work?

I cannot see a timer on the wiring diagram at all.

The wiring diagrams has wiring from the battery to the ignition and via some maxi fuses and relays to the heater block.

Wires 1706 and 1707 I assume are switched earths (from memory) at the ECU which basically go to Pins 58 and 85 (again from memory at the ECU).

So assuming everything else is in order with the wiring, the ECU must contain the instructions to switch the earths back to open (and hence disconnect the control circuit of both relays) after a set period of time.

Does anyone know or has anyone ever tested how long they should be on for or have ANY useful information please?

I really don't want the coolant heater to try and set the hoses on fire again.

I would doubt that a short in a glow plug within the heater block would could cause them to stay live.

Thanks in advance.

Really want to have the function working though I have read horror stories.
User avatar
xantia_v6
Forum Admin Team
Posts: 9003
Joined: 09 Nov 2005, 23:03
x 817

Re: Xantia HDi Water Coolant Heater

Post by xantia_v6 »

DickieG wrote: 28 Dec 2010, 20:02 Their purpose is as Imperial states to heat the water entering the heater matrix, they are controlled by the engine ECU via two green relays located either side of the pink headlamp washer relay within the fuse/relay box behind the battery.

The unit comes into operation a couple of minutes after starting the engine and remains on until the coolant temperature reaches about 80°c.

Removing the unit is a complete pain in the you know what as it is secured by two totally inaccessible Torx screws to a metal bracket held onto the bulkhead by two 13mm headed bolts which are located under about six metal hydraulic pipe's.

How do I know all this? Well the unit on my HDi is leaking in the joint between the two halves of assembly so I've managed to remove one from a HDi in a breakers yard which was a right old palaver.

You could potentially fit one to a petrol car but I'd wonder why you'd want to, apart from the additional wiring and water pipe adaptations you'll also need to upgrade the alternator to the 120 amp one fitted to HDi's fitted with this unit.

Having now owned a later HDi Exclusive with the Eberspacher diesel burning heater and now one with the glowplug heater, comparing their heating performance, the glowplug one gets going quicker but once underway (it takes the best part of 5 minutes) the Eberspacher one produces more heat to get the engine temperature up to operating temperature, ultimately swings and roundabouts.
Rhothgar
Donor 2023
Posts: 1733
Joined: 22 Nov 2004, 01:21
x 77

Re: Xantia HDi Water Coolant Heater

Post by Rhothgar »

xantia_v6 wrote: 09 Oct 2023, 18:58
DickieG wrote: 28 Dec 2010, 20:02 Their purpose is as Imperial states to heat the water entering the heater matrix, they are controlled by the engine ECU via two green relays located either side of the pink headlamp washer relay within the fuse/relay box behind the battery.

The unit comes into operation a couple of minutes after starting the engine and remains on until the coolant temperature reaches about 80°c.

Removing the unit is a complete pain in the you know what as it is secured by two totally inaccessible Torx screws to a metal bracket held onto the bulkhead by two 13mm headed bolts which are located under about six metal hydraulic pipe's.

How do I know all this? Well the unit on my HDi is leaking in the joint between the two halves of assembly so I've managed to remove one from a HDi in a breakers yard which was a right old palaver.

You could potentially fit one to a petrol car but I'd wonder why you'd want to, apart from the additional wiring and water pipe adaptations you'll also need to upgrade the alternator to the 120 amp one fitted to HDi's fitted with this unit.

Having now owned a later HDi Exclusive with the Eberspacher diesel burning heater and now one with the glowplug heater, comparing their heating performance, the glowplug one gets going quicker but once underway (it takes the best part of 5 minutes) the Eberspacher one produces more heat to get the engine temperature up to operating temperature, ultimately swings and roundabouts.
Many thanks for this.

So taking this ones step further, does it rely on the outside temperature being below a certain temperature as measured by the external temp sensor in the nearside mirror?

I ask because I've checked the relays and they are fine after being cleaned up.

I learned yesterday that if the slider switch is set to demist (I now understand the reasoning behind this) that the AC con is switched on albeit no lamp lights on the switch which in turn switches the radiator fans on. Until it was explained to me yesterday, it just seemed bonkers that you would immediately be cooling the engine and obviously have increased fuel consumption. I guess best practice in cold weather is to get the screen clear and then turn demist off!!! BONKERS!

I'll now crawl back under my rock and cogitate on AC issues that I have.
User avatar
xantia_v6
Forum Admin Team
Posts: 9003
Joined: 09 Nov 2005, 23:03
x 817

Re: Xantia HDi Water Coolant Heater

Post by xantia_v6 »

I believe that the auxiliary heating is controlled by the engine ECU, based on engine temperature.
Rhothgar
Donor 2023
Posts: 1733
Joined: 22 Nov 2004, 01:21
x 77

Re: Xantia HDi Water Coolant Heater

Post by Rhothgar »

xantia_v6 wrote: 15 Oct 2023, 13:30 I believe that the auxiliary heating is controlled by the engine ECU, based on engine temperature.
That would make sense.

Be nice if there was info somewhere that detailed it.

In reality, it should come on at any temperature below 80 really to get temperature up to required temp. Well certainly anything below 50 degC to give it a burst.

Having said that, primary reason is screen clearing I guess and not fuel efficiency.