Citroen c5 X7 - cabine heating problem?

[ExOduS442xb]

Since this is a "modern" (post cirka 1995) there is always coolant flow through the heater matrix.
The temperature is controlled only by the flaps in the heater box.
As you can see in the above picture there is no valve in the system.

The last Citroën with heater valve was the BX

So, the heater matrix should always be hot? No matter if you need to use cold or hot air?

[citroenguy]

Since this is a "modern" (post cirka 1995) there is always coolant flow through the heater matrix.
The temperature is controlled only by the flaps in the heater box.
As you can see in the above picture there is no valve in the system.

The last Citroën with heater valve was the BX

So, the heater matrix should always be hot? No matter if you need to use cold or hot air?

Yes, but only if engine can keep coolant temp high. But that's the problem in colder weather, a modern diesel won't. That's why you have PTC/"toaster" heater or Webasto diesel heater.
I'd try to feel if the PTC heater is hot when you set it to full heat in the cabin.

[CitroJim]

Before you go too much further the problem may be nothing more than an airlock in the matrix...

Give the whole cooling system a good bleed following the exact procedure for this vehicle... Marc should be able to advise on the procedure...

[ExOduS442xb]

Yes, but only if engine can keep coolant temp high. But that's the problem in colder weather, a modern diesel won't. That's why you have PTC/"toaster" heater or Webasto diesel heater.
I'd try to feel if the PTC heater is hot when you set it to full heat in the cabin.

I will definitely try to see if the PTC heater is hot.

Before you go too much further the problem may be nothing more than an airlock in the matrix...

Give the whole cooling system a good bleed following the exact procedure for this vehicle... Marc should be able to advise on the procedure...

That's not the problem, we did it on 2.7 hdi last year and it should be similar, I have procedure for this.

Regardless of PTC I think it would be a good idea to flush matrix, but I would like something that would clean the system as well.
Any suggestions?
There are some cooling system cleaners available and since heater matrix use coolant this should do no damage and still clean the system, hopefully.
Last thing I want to is to damage heater matrix.

[ExOduS442xb]

An hour ago I got on "Antipollution fault" with check engine light, with sudden loss of power, everything was fine until I stopped at the traffic light, and when I tried to accelerate the car was able to get to 15 km/h. I was able to leave the car in the parking and will return after work with Diagbox to analyze the problem.

[ExOduS442xb]

Hi guys, sorry for not replying but I was very busy with a lot of stuff, one of which was installing an RT6 unit in the car, but that's for another topic.

We've tried to flush cabin heater matrix, and it was not clogged. We first flushed it with water, afterwards we used Radiator Flush to clean the system https://abro.com/product/radiator-flush/ and left it within the system for about 30min. During the second flush with ABRO we just let it in the system via gravity, and it came out on the second pipe. First flush was pink due to antifreeze coolant, I am not even sure I saw any rust residue or anything else that could pollute the system. The 3rd flush consisted of only distilled water (all 5L).

Then I've went for a short drive (5-7min) and one pipe was very warm again (not to hot because of short driving) but the other was cold.
It really looks like something is ''holding'' the hot water from entering the system. Which also doesn't make sense, since the flush worked easy, without any problems.

Do V6 models use the same heater matrix as the other models?

I still need to check PTC heater, worked on it until 21h Yesterday.

Some pics of the procedure:

[Hell Razor5543]

This may be a silly question, but did you use a 'header tank' to refill the coolant? There are places in the cooling system that are above the expansion chamber, and so can end up without any coolant there. The way around this problem is to get hold of a second expansion chamber cap, some flexible piping and a large plastic bottle (with its cap). Cut the bottom off the bottle. You run a length of piping between the two caps and then, when you need to fill up the coolant system, you can use this 'header tank' for the final stage, as this should drive out any air in the system.

I know of somebody who has made this 'header tank' using two lengths of piping, with one length ending just inside the reservoir cap and a long way up the bottle. This helps air to escape while the other pipe (which ends just inside the bottle) allows the coolant to flow in freely. He hangs the 'header tank' from the bonnet, to give it sufficient height.

[ExOduS442xb]

I've tested again, but a little bit different. I've started the car without AC, and the cabin got warmer, warm air was coming through the vents. I've measured at one vent 29, the other 27, passenger 28 and 29 degrees so not to hot, I think it should still be warmer, but at least it's not cold anymore. I will probably flush the system again and add a pump with radiator cleaner again, it should circulate through the heater matrix for maybe 2-3h.

'OUT' pipe was warm, but not hot, and as soon as I started AC cold air started going through the vents and 'OUT' pipe became cold again.
This makes me think there must be something on the radiator that controls flow of the hot water/coolant trough the system.

Not sure what else could it be, with these symptoms?

@Hell Razor5543 I've bled it at the one of the pipes next to the I/O, don't think that's the issue, once I added distilled water (small amount) coolant started slowly going through the bleed screw and then I closed it.

[Paul-R]

... as soon as I started AC cold air started going through the vents and 'OUT' pipe became cold again.
This makes me think there must be something on the radiator that controls flow of the hot water/coolant trough the system.

Not really if you think about it. The water going in is warm and warm air comes out as ambient temperature air goes through. When you engage the A/C the air is cooled so much it overwhelms any heat in the coolant pipe and that's why cold water comes out.

[quzio]

I've tested again, but a little bit different. I've started the car without AC, and the cabin got warmer, warm air was coming through the vents. I've measured at one vent 29, the other 27, passenger 28 and 29 degrees so not to hot, I think it should still be warmer, but at least it's not cold anymore. I will probably flush the system again and add a pump with radiator cleaner again, it should circulate through the heater matrix for maybe 2-3h.

'OUT' pipe was warm, but not hot, and as soon as I started AC cold air started going through the vents and 'OUT' pipe became cold again.
This makes me think there must be something on the radiator that controls flow of the hot water/coolant trough the system.

Not sure what else could it be, with these symptoms?

@Hell Razor5543 I've bled it at the one of the pipes next to the I/O, don't think that's the issue, once I added distilled water (small amount) coolant started slowly going through the bleed screw and then I closed it.

I managed to solve the problem with the hot inlet pipe to the heater and the cold outlet pipe?
I have the same problem.