Windscreen demist doesn't blow hot air - what logic trap have I found?

[UK_MJN]

OK folks, my first new thread, a challenge born of frustration.

This morning I had to travel before dawn and it was cold enough for ice to have formed on the inside of the windscreen over night. So I started the engine, clicked the front and rear screen demist buttons and set about removing the ice on the outside. Rear screen cleared OK (only two broken heating wires).

5 minutes later and no hot air from any of the vents. Plenty of fan and air flow though. Puzzled. Cleared the screen by hand and set off. Pressed all the buttons (twice) to no avail. 9 miles later and STILL NO HOT AIR from the vents. Cycled the controls several times (to fully off, through ECON and screen demist on/off) and was starting to curse any number of deities when the hot air came on!

The OBDCIIC&C said 5 deg C intake by now. Clearly no blown fuses and the car starts and runs normally, no dash lights etc. Lots of assist

So what happened? How did I manage to convince the climate control system on a cold day that I only wanted lots of fan but NO heat when the screen demist button showed an orange LED?

Here's hoping for a simple explanation that I can use next time, winter could be a few months yet!

[MN Driver]

Check the heater mix valve under the hood, you'll see the two heater lines running to it, the small valve has a little lever connected to a cable. Make sure the cable hasn't come loose. If its on there cycle the temperature knob from the coldest temperature and check the position and the hottest temperature and check its position.
If the heater valve is opening and closing properly and you still aren't getting heat I'd suspect air in the system.

Check those things.

[spets]

The OBDC&C intake temperature doesn't matter since the cabin gets the heat from the coolant lines.

It is possible that the car hasn't warmed up yet so you didn't get the warm air if it was just idling for five minutes? But possibily like MN said it could be a sticking heater mix valve that doesn't like the cold.

[MN Driver]

I missed that part about idling. Idling for 5 minutes usually doesn't produce much heat unless you had the fan off completely and then you might get a little bit but you'd be best having the blower on low to feel it and get any usable light frost removal.

[AbCaRed00]

Page 13 of HVAC pdf in repair manual shows an illustration to determine what faults the A/C system may have.

How to read A/C DTC error codes:

To run the self-diagnostic function, do the following:
1. Turn the ignition switch ON.
2. Press the AUTO button and then the OFF button.
Continue to hold both buttons down.

If there are errors a bar will FLASH in the digital display pattern at left alternatively within the number '88' on the A/C screen on the dash")
_______________

To limit windows fogging somewhat: I try not to 're-circulate' the cabin air in misty conditions, [drawing instead fresh dryer air hopefully], and open a side window just a crack while underway.
As an afterthought: & Not sure if that 'goggle demisting stuff' used in some winter sports my be a good thing or not for your windows there, but maybe worth a try as the UK can be so humid.
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fwiw: I set the heater knob a few degrees above the lowest setting only, to help the engine temp rise a bit faster in the cold. Plus, i need use a simple cardboard radiator block, especially at highway speeds to maintain what heat does develop. The first gen Insight doesn't throw a lot of heat with only 1L in very cold condtions.

[retepsnikrep]

Screen fogging and condensation is a real PITA in UK cars.

First cause is likely to be leaking roof and moisture ingress that needs sorting along the lines of the wetseatbelt issues.

As far as the failure of the heater to work, as suggested check the coolant valve and the AC system for fault codes, if both working check air locks in cooling system.

Temporary solutions include using activated charcoal or silica gel bags to pull humidity down in the car. Personally I bought a proper portable de-humidifier and leave it in all our cars at least once a week/month overnight during the dampest months. It can easily pull a pint of water out the interior of my wife's leaky car overnight. Screen is beautifully clear then for a few days at least!

[UK_MJN]

Thanks everybody for the valuable suggestions - I greatly appreciate it, and will check the codes and mix valve at the weekend.

It's a good point about the engine not throwing out a lot of waste heat during warmup because it's so damn efficient!

[talonmike]

I think that this is the best solution. I did not know those kits. next time my lines don't heat again, I will buy this kit.

Can you post a picture of your installation on the insight?

[UK_MJN]

Sorry to report that the car didn't make it to the weekend...

The cooling system failed on Friday and the overheating car was recovered to a Honda dealer, who will look at it on Tuesday pm or Wednesday. I'm interested to know if the climate control blowing cold air was an early indicator of the failure. Too much of a coincidence for my liking.

I'm hoping it's a dead water pump (there was no coolant loss).

I'm not hoping the head gasket is gone...

Will give an update when I've heard more. First time the car's let us down.

[UK_MJN]

OK. Update from the main dealer: Head gasket failure.

They suspect head gasket - the coolant is going down but there are no external leaks. That points to it leaking into the engine and being released through the exhaust as steam. The misfires on 2 and 3 support this, but the syringe test fails to confirm it for sure. The price for the gasket set, including fitting and VAT, is £697. They can't get the original Honda parts until 11 January. Thermostat will be replaced as a precaution.

Merry Christmas folks!