Climate control acting funny after running a bit low on coolant.
 

Hello,

I'm having an issue with my heater...

The other day while sat in traffic I watched my water temperature gauge drop off, it was at it's normal half way and it just dropped off at about the same pace the fuel gauge climbs after filling up.

The traffic started to move as the needle was falling and I started to accelerate, instantly the gauge went back up to normal. I got home and topped up my water levels that were a bit low and topped up the expansion tank that was pretty empty..

Since this the gauge has worked normal but the in car temp is not working correctly.

The other day I drove around with the temp set to 24c and the blower was at speed one and blowing cool air, I turned the temp up to about 26c and the blower speed switched off???? If I crank it up to max temp the blower goes to max speed and good warm air comes through.

What's going on?

That's a really weird set of circumstances and nothing obvious springs to mind.

I think i'd start with checking the thermostat which you can do by checking the temperature of the top and bottom rad hoses from cold. Start the car up and as it starts to warm up the top rad hose should warm up a lot quicker than the bottom one, then when the car is up to temperature the thermostat will open and the bottom hose should start to warm up as coolant flows. If they both warm at roughly the same rate then its a sure sign that the thermostat has failed.

I'd also check the water flow valve on the bulkhead. It's connected to one of the two coolant pipes which go into the heater matrix. When the heater is on max hot it should open to allow coolant into the heater matrix. When on max cold it should close to stop coolant flowing through the matrix. You can see it easy enough and should see it's lever sitting in two different positions depending on if you have the heater on hot or cold.

The other thing i'd do is check the carpets in both the passengers and drivers footwells to make sure they're not damp. :(

I don't understand how if I turn the temp to max You can hear the motor turn the vent to the matrix and hot air comes through.
If the thermostat was knackered wouldn't the car run cooler than norm? Watching the water temp gauge it starts to warm up after the same amount of time and and the needle climbs to the same point.

Is the hot air coming through definitely as hot as it used to be?

Maybe not...

Top rad hose is hot but not rock hard...
Bottom rad hose is lukewarm. Car has been driving for 15mins temp gauge is at running temp.

.Edit.
ok I'm thinking this is normal, I've trundled across town from work, weather is cold. Probably hasn't warmed up yet.

What sensor tells what temp it is in the cabin and what tells the fan and vent system what to do?

The cabin temperature sensor is in the little vent (about 1.5cm square) near the clock.

ok try this.

Fan on auto, slowly turning the temp up from 20 to max, I can hear the paddle behind the dash working the air flow system, fan speeds up to 2 about 25c, as I get to 27-28c the fan switches off as if the water is cold. Turning to max and fan goes to max and hot air comes out.

That is a little weird.

There are actually some built in diagnostics you can do on the AC system, let me see if I can dig out the instructions.