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[Strangechap]

Ok, so my matrix was blocked a couple of months back, flushed, all sorted. Was blowing nice and hot.

Until Tuesday last week.

On the way back from Bracknell to Reading after my sprog's swimming lesson, the heater suddenly started blowing cooler and cooler until it was freezing. Cue moaning from the wife, who hates my car anyway.

Got home, checked the matrix hoses, both hot. Reset the climate panel 3 or 4 times. Few starts and stops of the engine and quite a lot of naughty words.

Then it starts blowing hot again.

Been fine all week.

Then, last night on the way back from Bracknell again IN EXACTLY THE SAME POINT IN THE JOURNEY it starts to blow cold again. Cue more moaning from the wife.

I had replaced the HBV 3 weeks ago with a used part which I 'assumed/hoped' was ok. Came of a scrapper I had for parts. Mine was leaking, this one doesn't.

Strikes me as odd that it went cold in the same place on the same day. It's not the longest journey I've done since, and the heater hasn't gone cold at the same driving time into any other journey I've done, including the way THERE.

So, any ideas? Does this sound like my used HBV could also be faulty?

It never did this BEFORE I replaced it. Law of coincidences suggests it may be related to the HBV.

Anyone suggest anything else, of should my first job be to fit a brand spanking new HBV?

Cheers.

[Entwood]

Whip the vacuum pipe off the top of the HBV and block the pipe with a small bolt, leaving the top of the HBV open to atmosphere. See if that improves things ...  could well do so, especially if the HBV is a tad "tired" being pre-used ..

[dbug]

You've answered your problem mate - take a different route 

[Strangechap]

Thanks chaps.

Lol. Or avoid Bracknell altogether, obviously not good for me!

Did it again last night, only on a short journey too. (in Reading this time!)

Seems odd that it's then fine this morning. (Thank god)

Will try the vacuum pipe off at the weekend. See if it still does it.

As I understand it, that should make the HBV default to 'Hot'?

So as the vacuum controls the HBV, is it the HBV that helps decide the amount of heat to the matrix and therefore the car interior? I'm guessing the heater panel also uses fan speed to adjust temperature too.

Or does the HBV just cut off heat altogether when the AC is on?

[Abiton]

Thanks chaps.

Lol. Or avoid Bracknell altogether, obviously not good for me!

Did it again last night, only on a short journey too. (in Reading this time!)

Seems odd that it's then fine this morning. (Thank god)

Will try the vacuum pipe off at the weekend. See if it still does it.

As I understand it, that should make the HBV default to 'Hot'?

So as the vacuum controls the HBV, is it the HBV that helps decide the amount of heat to the matrix and therefore the car interior? I'm guessing the heater panel also uses fan speed to adjust temperature too.

Or does the HBV just cut off heat altogether when the AC is on?

Yes

[Strangechap]

So, the problem is getting worse. Each time I drive the car, it will go cold on some point on the journey.

When I go to drive home, the heater will be working again. For a while.

I've pulled the vac from the HBV, makes no difference.

The top hose to the matrix is red hot all the time, the bottom one only warm, which leads me to believe the matrix may be clogged again, BUT, the symptoms are very different.

Before, when the matrix WAS blocked the heater never got hot, now it does.

Before, an increase in fan speed would lower the vent air temp, a decrease in fan speed would increase the vent air temp a bit. Now when it goes cold it stays cold.

It gets so cold so quickly it's almost like the air is suddenly diverted from the matrix.

Have tried the climate reset trick: No difference.

Could the climate panel be up the spout?

I'm not convinced its a cooling system issue, rather a climate problem.

I have a spare climate panel. Worth fitting it?