Volvo 940 only blowing cold air

[Ian21401]

Thanks Dave but I think that my link error was strictly down to my inexpertise.
Isn’t internetechnology wonderful, until it doesn’t?

[Laird Scooby]

Originally Posted by Ian21401

Thanks Dave but I think that my link error was strictly down to my inexpertise.
Isn’t internetechnology wonderful, until it doesn’t?

Just like all the other wonderful inventions in the past 20-30 years Ian, fantastic when they work, worse than uselss when they don't!

[McGandalf]

Originally Posted by Ian21401

My two pennorth, for what it's worth...

That's better.

Many thanks. Excellent advice and pictures.

I may just count my losses, write off the £18 worth of fresh coolant I have in the system (I appreciate I *might* be able to theoretically reuse it, but to be honest I just want to get to the bottom of the problem), and do a full re-drain, re-back flush and veeeeery slow refill.

Will investigate the position of the HCV when the coolant is drained and I can disconnect the hoses in the cabin.

I have read about the Mk 2 Golf HCV replacement dodge - and I actually have such a valve kicking around - but I'm assuming the valve on the car is ok for the moment.

I've been undoing the engine block drain plug by reaching from the underside of the engine, but this is a pain - is is feasible to access it from the top?

Really want to get this sorted - taking the old girl for a long-ish run the other day prompted a barrage of "my feet are freezing" comments from my wife!

[Laird Scooby]

You need to find out why there appears to be some sort of blockage in the system before deciding to lose the coolant you've just put in. Also follow the steps i outlined for a drain, backflush etc earlier in the thread - once the water runs clear you need to remove the bottom hose and drain the system, there's no real point using the drain tap on the block if you remove the bottom hose.

I'd be looking for an additional domestic service valve that someone might have installed in the system or some other rerouting of the hoses.

[griston64]

Originally Posted by McGandalf

Many thanks. Excellent advice and pictures.

I may just count my losses, write off the £18 worth of fresh coolant I have in the system (I appreciate I *might* be able to theoretically reuse it, but to be honest I just want to get to the bottom of the problem), and do a full re-drain, re-back flush and veeeeery slow refill.

Will investigate the position of the HCV when the coolant is drained and I can disconnect the hoses in the cabin.

I have read about the Mk 2 Golf HCV replacement dodge - and I actually have such a valve kicking around - but I'm assuming the valve on the car is ok for the moment.

I've been undoing the engine block drain plug by reaching from the underside of the engine, but this is a pain - is is feasible to access it from the top?

Really want to get this sorted - taking the old girl for a long-ish run the other day prompted a barrage of "my feet are freezing" comments from my wife!

On your first fill did you run the car with the cap off for a little while and burp the system ?

[Laird Scooby]

Originally Posted by griston64

On your first fill did you run the car with the cap off for a little while and burp the system ?

He says he followed my method (in post #9) to the letter Mark so i would assume so - i burp the system before running it but the end result is the same.

[Ian21401]

Originally Posted by McGandalf

Many thanks. Excellent advice and pictures.

I may just count my losses, write off the £18 worth of fresh coolant I have in the system (I appreciate I *might* be able to theoretically reuse it, but to be honest I just want to get to the bottom of the problem), and do a full re-drain, re-back flush and veeeeery slow refill.

Will investigate the position of the HCV when the coolant is drained and I can disconnect the hoses in the cabin.

I have read about the Mk 2 Golf HCV replacement dodge - and I actually have such a valve kicking around - but I'm assuming the valve on the car is ok for the moment.

I've been undoing the engine block drain plug by reaching from the underside of the engine, but this is a pain - is is feasible to access it from the top?

Really want to get this sorted - taking the old girl for a long-ish run the other day prompted a barrage of "my feet are freezing" comments from my wife!

I managed to access the engine block drain plug from the top and would do it anyway, but as Dave says, it may not be necessary.

I definitely would not disconnect any HCV hoses in the cabin as they are a PIA to reconnect and, in my opinion, removing the HCV is absolutely a last resort. If you disconnect it’s control cable and are able to move the operating lever through it’s full movement you should be able to ascertain whether it is moving freely. As previously stated, if more than 8 litres came out when you initially drained down then it would appear that the valve was open then.
To check whether the matrix etc. is clear, why not remove both heater hose ends from the engine end ( the one under the inlet manifold and the one onto the rigid pipe to the water pump ) and try flushing through with a hose pipe. That way you won’t be likely to damage the pipes through the bulkhead.
Daft thought. As you have replaced the thermostat it should be easy to remove it again. Why not remove it and refill the system from there until it overflows then replace it and slowly complete the refill via the expansion tank.

[Ian21401]

Re removing the HCV.
Having looked back in my notes from April 2008 when I replaced mine.
It’s a long time ago and I may not be remembering it exactly but here goes....
The HCV is located into a “control housing” which is located into the bulkhead by two lugs on a bayonet type system. So to remove the HCV itself, the control housing needs to be removed complete with HCV. (and the clutch pedal needs to be removed to do that ) There are two control cables to the HCV. The lower one is operated by the dashboard control. The plastic lever on the HCV also operates a cam which moves the upper cable which I was informed operates an air intake flap to allow air into and through the heater matrix. So when the heat control is operated the lever and the cam should both move.
There’s an old thread somewhere about it.

Edit:
I’ve managed to find some more details re the HCV operation.
It’s difficult to explain but should become obvious if (hopefully not ) you need to remove the HCV.
The temp.control cable operates a lever on the control housing which pivots at the top right hand corner of the housing. A concave cam on that lever moves the valve’s lever. The control housing lever also operates the air flap control cable. But hopefully this will not be relevant.

[Laird Scooby]

Originally Posted by Ian21401

Daft thought. As you have replaced the thermostat it should be easy to remove it again. Why not remove it and refill the system from there until it overflows then replace it and slowly complete the refill via the expansion tank.

It's not a daft thought at all Ian, it's a very good idea and one i was reserving as a last resort as i've only ever needed to do that on "serious problem" cooling systems. :thumbs-up:

Might be the way round whatever is causing the problem here but i have a gut feeling there's a blockage somewhere and your other idea of flushing just the matirx is also a very good one, next step in the diagnostics for now i reckon!

[Ian21401]

I’m trying to find that old thread from 2008 or later but my post history only goes back to 2019.
Is there a way of searching much further back, or is that deleted now?