240 General: Very Low Heat Output After Heater Control Valve Change

[TheHungriestBadger]

Hi All,

Hope you've had a good few months, I'm now finally finished with university 😁 so what better way to celebrate than prep for the summer and make sure my heating isn't stuck on full again.

I've replaced the heater control valve with a metal equivalent courtesy of Brookhouse Volvo (great people, I highly recommend). I certainly don't have heat stuck on full now which is definitely a plus, but I also now have barely any heat at all. Car is getting up to temp properly (according to the gauge, feeling the top rad hose, and a thermal camera on the thermostat housing). But as I say, almost no heat output. The two hoses going to the heater control valve are hot like the top rad hose, but the third hose going from the heater matrix to the firewall is stone cold. I can provide pictures of these tomorrow if it would help.

To do the repair with minimal mess, I drained the coolant through the lower rad hose, and then proceeded with the replacement of the control valve. I the refilled the coolant, and (I think) bled the system with the expansion tank cap removed and running up to temp. I had the heater on full whilst running up to temp and it did get lukewarm (i.e. definitely above ambient).

I took it on a quick drive of a few miles and switched the control valve to cold to verify that it could at least turn the heating off, but basically no heat came back which is definitely not normal by my previous year's experience with the car. Temp gauge remained rock steady which is something at least, and no leaks.

The only thing I'm not sure of is whether I had the control valve open (i.e. set to full hot) whilst actually pouring the new coolant in. Could this be the symptom of an air lock in the heater core or something? If so, is there a relatively easy and non-messy way to bleed this? Or is it a case of dump the coolant and try again (not optimal, but easy at least).

[Bugjam1999]

Hi,

A few comments - and a labelled photo would no doubt help.

There's no need to do anything other than set the heater to hot inside the car to bleed the system.

What kind of valve is the replacement? I stopped one of the complicated valves with a thermostatic switch inside it from working properly on my car some time back by overtightening one of the jubilee clips holding a hose to one of the outlets which deformed the body and jammed the thermostatic plunger inside.

Are you sure the valve is opening all the way? is there any adjustment on the cable? Did you check it opened etc. before fitting it?

You may need to remove it to check which is faintly annoying, but at least it isn't too hard to access.

Cheers

[TheHungriestBadger]

All fixed... For now, I think it may have been a combination of problems.

The biggest culprit was the control cable not being on properly (or in fact, at all, maybe?). The original metal valve had a hole and grub screw holding the control cable to the actuating part of the valve. The new one has a hole where the cable is supposed to be bent around to hold it attached to the actuating part.

For now, I have put in a (roughly) 90-degree bend in the end of the cable which allows it to 'pull' the actuating lever forward to the 'full hot' position. Due to the geometries involved though, the cable just pushes straight through the hole when attempting to set it back to full cold. To prevent this, I just wrapped a very thin strip of electrical tape many times around both the cable and actuating lever. It appears to be holding for now, although I don't know how 'permanent' this solution will be. If anyone has better methods for 'converting' the cable from the grub screw configuration to the necessary bend, that'd be great, although the wire used is incredibly stiff, and access is rather poor - even more so given I'm right-handed.

I did also loosen the clamp on the control valve end of the hose that connects the control valve to the heater core and squidged the tube until coolant appeared at the top of it. Following Bugjam's advice (thank you 😊), I tightened the jubilee clip, and then backed it off half a turn just in case there was excess pressure applied to the control valve body. I then repeated the coolant system bleeding procedure (run up to temp with expansion tank cap removed) and heard a lot of gurgling sounds coming from the control valve area. Still no leaks though, and these have now stopped after a quick drive, so all good there.

I now have furnace-like heat, and ambient air available (and presumably all the in-betweens as well, although I can't say I've tested this yet).

I will (at some point) take a bunch of pictures at some point just for future reference to anyone else who has this issue.

EDIT: Regarding the cable attachment issue, superglue is pointless, and I fear epoxy would be too. I tried a combination of UHU Ultrafast and Repair Max, and neither held the cable in place for even a single actuation (i.e. full hot to full cold and back again), even once both glues were fully cured. In theory, I could attempt to solder it, but that will be near impossible given the sheer amount of metal acting like a giant heatsink, plus makes future adjustment equally as difficult. These are both a no-go.

[Bugjam1999]

I think a pushrod connect for a radio controlled plane/car/boat will be what you need.

Something like this:

https://www.ebay.co.uk/itm/394049469...mis&media=COPY

With the end with the nut through the hole on the actuator arm for the valve, and the rod through the other side.

Or, if there is enough space on the end of the rod after it passes though the lever, perhaps you just need one of these:

https://www.ebay.co.uk/itm/283827738...mis&media=COPY

Cheers

[TheHungriestBadger]

Well blimey, I've had the full spectrum now: Started with no heat, fixed that, then had a nightmare attaching the cable, then had it stuck on full heat again, and now I've fixed that but had to detach the cable again (which I'll re-attach properly as per BugJam's post).

So, the brand new heater control valve was stuck on full, even with the cable disconnected, and the control valve actuator 'clicked' onto full cold by hand. Turns out the thermostatic adjustment screw was off (the one poking out from the middle of the front of the mechanism towards you). I had a look at this page (Full URL: https://240seriesparts.com/tag/volvo...control-valve/), although it didn't mention which way to adjust the thermostat screw for a desired outcome (i.e. one way for hotter, the other for colder).

From experimentation just now:

- CLOCKWISE = COLDER
- ANTI-CLOCKWISE = HOTTER

Hopefully, this completes an otherwise excellent write-up by the linked article (and yes, I have archived that page so it should always be viewable on the Wayback Machine).