No cabin heat

[Ikeaboy1]

Today was the first cold day of the season, and I discovered I have no interior heat.

My mode switch was rebuilt this spring by dpi and my AC works beautifully. I doubt this is the issue.

I did an interior refurb and had the entire interior apart. It would've been pretty easy to knock the heater control vacuum hose loose. I suspect this is my problem. Any tips on how to confirm this before tearing the interior apart again?

[DMCMW Dave]

The no-vacuum position of the water valve is open (heat). Remove the vacuum hose from the valve and see if the valve opens. You should be able to push it closed and see it spring back open. Also see I'd the hose is warm on both sides of the valve to verify water flow.

If you knocked the hose off you would have heat BTW.

[Ikeaboy1]

Thanks Dave. I'll warm it up in the morning and try see if I can feel heat on both sides of the valve. I can actuate it by hand and it springs back.

If it's not a loose line, what's the next logical thing? The coolant has been flushed and refilled and an auto bleeder installed.

[Jonathan]

What about the heater cable? (from the temperature selector knob) I ask partly because I'm not sure myself where it goes and figure we'll learn here about it from someone. Maybe it's not connected as it should be?

[David T]

What about the heater cable? (from the temperature selector knob) I ask partly because I'm not sure myself where it goes and figure we'll learn here about it from someone. Maybe it's not connected as it should be?

With the motor running and the heater on feel the 2 hoses going to the heater core. You can reach them inside the front, right wheel well. If they aren't getting hot you have to figure out why. Kinked hose, blocked/stuck heater valve, blocked heater core, disconnected hoses. If they are getting hot you have to see why you aren't getting hot air. Actuators not moving correctly etc. BTW if the motor is not getting hot you won't get heat. Is the motor getting up to operating temperature? A stuck thermostat (or none at all) can also cause no heat. Low coolant can also cause a no heat.

[DMCMW Dave]

What about the heater cable? (from the temperature selector knob) I ask partly because I'm not sure myself where it goes and figure we'll learn here about it from someone. Maybe it's not connected as it should be?

It can be disconnected but it would be very obvious as the knob would be way too easy to turn.

I did find a car where someone bypassed the heater core on purpose (probably a leaky core, and/or a southern car where they didn't care) but if yours used to work and doesn't now that's probably not the case. It's also possible (rare) that the arm that rotates the valve has become loose on the valve and isn't really turning it. The hot/cold hose test would show this.

I find a stuck thermostat will allow heat when going down the road but it may cool off at idle.

The first thing is to figure out if it's a lack of hot water or the air is not being directed through the heater core.

[Ikeaboy1]

I got the car good and hot and I seem to have heat now. Perhaps the car hadn't gotten hot enough to open the thermostat yesterday...

Now I seem to have another weird issue. The car won't switch out of defrost mode. Always chasing something...

[DMCMW Dave]

I got the car good and hot and I seem to have heat now. Perhaps the car hadn't gotten hot enough to open the thermostat yesterday...

Now I seem to have another weird issue. The car won't switch out of defrost mode. Always chasing something...

That's gonna be the mode switch. My guess is that the rubber diaphragm is not attached to the rotating disc any more. For a while it was stuck in "max" which turns off the hot water, and now it's stuck in "defrost" which will give heat but blow it all at the glass.

[Ikeaboy1]

This makes sense. I hear no hissing. Could I pull and resecure the seal or will it need to be replaced?

[DMCMW Dave]

This makes sense. I hear no hissing. Could I pull and resecure the seal or will it need to be replaced?

If the disc is simply stuck in place it may not hiss.

You take apart the mode switch. You can sometimes glue the rubber disc back in to place but if the tits are torn off it's better to replace it (can't wait to see the replies to that one!).

[Fox2506]

Check the heater core foam seal in the driver foot-well where the pipes come out. Without that foam, air exits the duct work before passing the heater core. Makes air coming from the vents feel weak and lukewarm.

Probably not the problem, but good time to check it to ensure you get the most out of your heater.

[Kozmatic]

if the tits are torn off it's better to replace it .

Life lesson right there...

[Bitsyncmaster]

If the disc is simply stuck in place it may not hiss.

You take apart the mode switch. You can sometimes glue the rubber disc back in to place but if the tits are torn off it's better to replace it (can't wait to see the replies to that one!).

When end face some metal on a lathe that little center bump is called a tit. Should have seen the machine shop class crack up with that lesson.

[er1c]

Just thought I would add to this thread in case it helps others.

On a chilly November day yesterday it was dry for once so the DeLorean had a good 60 mile run which we froze on. Heating was working previously no changes since, engine was up to temp and the rad hoses in/out were warm.

The Hot water valve switch was clearly jammed closed stopping hot water getting into the heater matrix. Sprayed with WD40 and gave it a wiggle and et voila... the cabin heating is working again.

I have ordered a new switch as for the sake of ?24 I understand they corrode and break down so it was going to happen anyway and may well happen again.