Is this used by both the air con and the heater?

I ask because neither works. The air con I suspect needs a recharge at the very least but the heater pump whirs and the shuttle valve clonks so my suspicion is that the heating is never triggered. The air con has error 14 plus 44 & 46 so I'm trying to get the heater to work first.

 

Put the heat on max, this should bypass any feedback.

If you unplug the heater valve, it defaults open. You should have TONS of heat.

The external temp sensor under the bumper is also a factor in this. I believe it fails high but still gives a reading on the main display.

I have had massive changes in heat following a cleanup of the heater core. Just undo the feed and return hoses off the firewall, and plumb a garden hose for fresh water. Use radiator cleaner in between the flushes. Use forward and reverse flows for best results. Flush may not come up with anything spectacular (deposits, debris, etc.) but the result was there for me.

Best of luck, keep us posted.

 

The sensor under the bumper probably works as it reports the ambient temperature on the display accurately. I tried the heater on Hi but got no heat. I'll try disconnecting the valve next time I take it for a run - I had forgotten the valve defaults open. I do have both hoses hot.

I saw that your matrix flush worked for you. Won't I lose a lot of coolant from the hoses I have removed to flush? If that's not a problem then after trying taking power off the valve I'll flush!

 

From memory, the 2 hoses to the core are pretty high, but use a turkey baster and get some coolant off the expansion tank. You will need these long hose pliers. One of the hoses to the core has a weird flat section to it, supposedly by design, to accommodate that one-way valve. Might be worth just replacing it in case that flat section collapsed and prevents flow (hard to tell). Maybe temporarily replace this with a section of hose to see if there is a difference.

You also need to make sure the heater pump works. It is the more common problem. They run pretty much all the time, hot or cold, so the carbon brushes wear out. When that happens, I believe the circuit fails open. Find the fuse location and try to check resistance to ground from that location. A few Ohms is ok, "infinity" is open circuit and you need to rebuild the pump (hard to get to, but cheap and manageable to do in the garage with basic soldering skills). A new one is $$$.

Best of luck, keep us posted.

 

Thanks for the information - turkey baster!

The pump runs but who knows if it works although as I recall if you can feel them running then they should work. I can measure the resistance, another job for tomorrow.

Yes, I'll report back with progress. Being in the UK the heater is rather important.

 

Hang on, I still don't know if the air con and the heater both use the cabin temperature sensor

 

Went for a run

Tried Auto on Hi - no heat
Disconnected the valve - no heat

The pump does vibrate so I am assuming it's trying.

Flush next I suppose. Bother.

 

If you have an IR thermometer, you can check temp at various spots in the various circuits. This will tell you what is hot and what is not. The main loop of the octopus hose should be hot, the heater core circuit feeds off of that loop. You can also feel by hand if the hoses to/from the core are warm to the touch. Ideally the feed should be much warmer than the return. On my car, they felt kind of the same, which explained the lack of heat transferred to the cabin.

That is a semi complex system, and the lack of easy access to the valve and pump makes it sort of hard to pin point what is happening. You can have theories (valve is stuck, pump ok, but impeller is stuck, collapsed hose, one-way valve stuck, etc.), but all these scenarios call for bypassing stuff that is basically unreachable for quick debugging. So you have to start with a clean base, then eliminate electrical issues, before putting further work in.

 

I do have an IR thermometer and I have zapped various hoses. The two hoses to the valve differ by a small amount which as you say suggests why the cabin gets no heat.

In truth it's probably the pump brushes and I have seen a post that explains the cheap DIY fix but I think a flush is probably the next step. It will have to take a place in the queue of jobs though, the lower rear shock bush is currently head of that queue.