Heater not working

[SBL]

Well it finally has become chilly in Florida, and I need to troubleshoot my heater, which provides no heat.

I have never seen a drawing or description of the heater connections and controls, including the mechanical heater temp control, the hot water valve, and the vacuum and cooling system connections, all in one diagram/description. I am not seeing that in the service manual. I just can't pull it together from the fragments. I had a full rebuild of the AC and engine cooling system by DMC-FL, including the hot water valve, but they forgot to check if the heater works. Given the drive, I would prefer to tackle this myself and see where it goes.

A few things come to mind right away: check vacuum at the hot water switch when heater is selected from the mode switch, see if the temp control switch changes the plunger in the hot water valve (?), see if the lines going to the heater are hot (by feeling them after taking off the cover inside the hood), see how the flaps change when the mode selector switch is turned to various positions. On the latter, I hear doors opening and closing, and air goes to the floor (heat), the windshield (defrost), and floor and center outlets (bi-directional). None are ever even close to warm.

So any suggestions as to how to proceed would be appreciated and/or an explanation of how it is supposed to work.

Thanks

[WHO1DMC]

The hot water valve is located behind the engine on passenger side. Should be open all the time until you select vent or A/C mode. Unless it was put in backwards. But I don't think they would do that. The vacuum Connection should be to the left. It is easy to find and see you might need a flash light. Usually if it gets stuck it will be in the open position rarely closed. I'm going by experience in a cold climate.

Dave B.

[Rich]

So any suggestions as to how to proceed would be appreciated and/or an explanation of how it is supposed to work.

Refer to the DeLorean Workshop Manual.

N:01:01 to N:01:09 explains how all the flaps/doors are meant to work in response the the climate control settings, specifically the mode switch and the temperature switch.

As noted the hot water valve is normally open all the time. You get heated air when the flaps are arranged so as to pass air through the heater core inside the main housing. Could be bad linkage, busted flap, bad mode switch, bad diaphragm for the flap(s), other things?

[SBL]

I bet that the heater itself is not getting any hot water. I will check this weekend.

[David T]

A few quick checks you can do. Feel the hoses in the front right wheel well. If they aren't getting hot, hot water is not circulating. Assuming the motor is getting up to operating temperature, the heater circuit is plugged up if the hoses don't get hot. Could be the valve is stuck, could be the heater core is plugged up. Before you get into the flaps , if the heater core isn't getting hot you will never get any heat.

[TTait]

If the car has been in the south, or Florida for any period of time its also possible that the Heater has simply been bypassed. Not an uncommon thing to do in the south. Its a rather common mod as it can help improve the AC performance if the heater controls aren't keeping the heat off properly.

Depending on how you prefer to check it you can get to the two hoses behind the AC accumulator in the passenger front wheel well, or you can remove the spare tire and six or eight screws and find them easily near the fuel pump by removing the fuel pump access plate. IMO that may be easier than laying on the ground with the engine running. You are looking to see if both hoses are in fact there running into and out of the heater, or if they have been replaced with a U Hose to bypass the heater core. Maybe two U hoses, one to loop the water back and one to seal up the heater core from the elements. Maybe there is a manual cut off valve here you need to open, or maybe there is just a locking clamp on one of the hoses (no offense, but it is Florida).

If it looks normal, two black hoses running from the feed and return pipes hooked up to the two pipes from the heater core poking thru the firewall, then grab them and see if they are hot. If the engine is running and at temperature, they should be.

No matter what, you have just gotten really valuable information. If they are not hot, but the engine is running at temperature then there is either a manual cutoff valve next to your factory heater valve in the engine compartment, something has been re-plumbed, the heater core is totally plugged (unlikely), or the heater valve has failed in a weird way also unlikely.

If they are hot, but the heat isn't really making it out of the dash, then you have a problem we need to find in the hvac box under the dash. Either way, go turn the controls to cool and turn it to MAX AC for a few minutes and make sure they cool off - this tells you that the valve in the back is at least working properly.

Go see if hot water is making it to the heater core and let us know. Either way you choose - no tools and lay on the ground by the passenger wheel or pull that panel under the spare tire, it won't take but a couple minutes and it will quickly narrow the problem down to a specific area.

[mr_maxime]

I never managed to fixed mine before removing the engine, but I didn't have heat and found my thermostat had been stuck open.

[SBL]

Weekend is here!

I found the following:

At rest the plunger to the heater valve is out (which I presume is open).
At running temp, heater on:
The hose from the heater bottle is hot.
The hose going into the valve (driver's side on my car) is hot.
Hose leaving the valve (passenger side) is not hot.
Vac line connected, and when turned to max AC, plunger goes in.
I cannot find a "cutoff" valve in any of the heater hoses.

So, the valve is either dysfunctional (new and installed by DMC-FL), or there is a severe blockage. I would think that even with a near complete blockage in the input heater hose, that there would be some heat at the very edge of the hose where it attaches to the valve. But there is not. This makes me want to think that the valve is faulty.

I suppose I could remove the intake hose at the heater core and see if there is water flowing as final proof. Looking at the core, which hose would that be?

[Ron]

The heater core's upper hose is the supply .

FWIW, the heater core is relatively delicate -- Cut and peal the hose off rather than pull it.
..But I would check at the water valve instead, since it is the same line and you can bypass the valve with a pipe for a test.

[TTait]

If anyone has worked on the car before, heater cores are generally considered non directional so the feed and return hoses could have been hooked up to either of the lines on the heater core. Even if the factory was supposed to hook them up with a preference, some cars might have gotten through backwards because it really doesn't matter.

I was unaware they are fragile (good tip) - so before you mess with them, and because the problem is likely your valve, why not run to the auto parts store or hardware store and get a short section of rigid tube to replace the heater valve temporarily.

Let the car cool down till the coolant is room temp. Disconnect the passenger side hose from the heater valve, lift it up a little and clamp it down on half of the new rigid tube, then do the same with the drivers side hose. Keep the valve hooked up to the vacuum line and pull it over to the pontoon. blow thru it to see if its full open or closed.

Now warm the car up and see if hot water flows all the way to the heater core. Also, set the car to MAX AC and see what the valve is doing - if its opening and closing properly, can you now easily blow thru it?