Been looking into the function and controls of the Cortina heater system, mainly to figure out how to add a/c without resorting to the frequently used recirculation systems usually used for upgrading to air con.
The Cortina heater regulates heat by mixing two air flows, one through the hot matrix, the other, at ambient, bypassing the matrix. There is no control for setting matrix coolant flow (unless you fitted one in an attempt to keep the interior cooler in summer). The advantage is instant setting of cabin temp, the drawback is unwanted heat flow from the hot matrix into the interior.
The lower control in my car (73 130/5) has the usual three positions:
OFF - DEFROST - INTERIOR (there are earlier layouts with just DEF - INTERIOR markings, but they seem to work the same)
The bottom flap controlled by the this control has the corresponding three positions:
OFF/ flap up: this blocks the bottom outlet of the heater matrix
DEFROST/ flap in middle position: this shuts off the lower HEATER outlet so that all flow is forced up through the front screen vents. The fascia vents always receive ambient temp air.
INTERIOR/ flap down: this allows air into the footwells
What puzzles me: why would one ever use the OFF state as the airflow at OFF and INTERIOR is exactly the same (free flow into footwells). The only difference being that in hot weather and the heat control set to COLD, the heater matrix is shut off both at its upper AND the lower surface. This may reduce heat from the hot matrix seeping into the cabin. In OFF the temp control lever is ineffective - all air into cabin will be cold.
What am I missing?
Any theories on this appreciated, sketch attached.
My plus2 heater has no water valve to control temperature by opening or restricting coolant flow in the heater matrix so in effect, the heater is always at engine temperature and instead, the cabin temperature is regulated by opening or closing airflow thru the heater box.
I believe this arrangement is the same for all plus 2 models..Baby Elans have a more conventional arrangement with a cable operated heater valve at the thermostat housing..
Your drawing has me wondering what the off position actually feels like for strength of air flow out of the eyeball vents. I feel a noticeable reduction in eyeball flow in the interior setting, and therefore have been using the screen setting in hot weather. Perhaps the off position would be a better compromise for hot weather.
Like others I have installed a manual inline coolant valve in the heater core circuit under the bonnet. Really makes a noticeable difference in hot weather and highly recommended.
Too cold here to try out the heater, but I will definitely try the off position next spring.
as it often happens, just writing things up may bring new insights. It occurred to me that it might have been useful to look up the heating and ventilation section in the owner´s manual. Problem is, I don`t have one and so far have not found one.
It seems that the only way of blocking air from the cabin at all is to move the two levers to the left - where the markings clearly say OFF with two fat arrows to the left (in the later cars anyway). And indeed, with both levers in that position and the two face vents shut, there is only some air admitted to the screen vents. Personally I have never seen the need to do this but it is conceivable that in a long, stinky tunnel with heavy traffic this might be desirable.
The other point which I have never ever seen mentioned when the ubiquitous mod of adding a (or even two) stopcocks to the heater supply hose(s) is suggested is the following:
The coolant thermostat design in the Elan does not include a direct passage of coolant back to the block with the thermostat CLOSED (cold engine) UNLESS the heater circuit is open. When the heater passage is blocked, the water pump cannot circulate coolant at all. This prevents the uniform heating up of block and head until the thermostat starts to open. Not a good thing, but apparently Twincams do survive this. This is my main reason for not applying this option.
I’ve watched this discussion in several threads over the years and wondered if anyone has tried a three-way brass manual ball valve. The input hose to the heater core would be connected to the input of the ball valve and one of the outlets would go to the heater core inlet and the other would tee into the heater core outlet. In one position the coolant would flow through the heater core and in the other position it would bypass the heater core and return to the cooling system. Any position between would mix the coolant flow between the two. This would eliminate the blocking of coolant during warmup with the heater core blocked off.
They are relatively inexpensive and readily available.
There was a trick in Mini racing circles years ago of drilling a 1/4” hole in the thermostat to maintain some flow but to also allow the engine to warm up at a sensible rate to allow the thermostat to open. Neater than ball valves maybe…
Either would work - better than blocking the hoses anyway.
Since I need to take everything apart anyway my solution will be to add thermal insulation to the heater box in the area of the heater matrix. I like fit-and-forget, be it cold or warm
Years ago I put a valve in the heater supply circuit, just after the thermostat housing, I switch it off in the summer and on in the winter. I always intended to put a switchable valve that operated when the lever in the cabin was set to cold but I never actually did it.
It’s never been an issue and prevents the cabin getting to hot in the summer.
Ed
I did the air-conditioning in my +2, but it’s you I think indicated you don’t like the idea of just recirculation, but that’s the way the system set up but then it has heat and defrost and air conditioning (Vintage air “mini unit”, all behind the dash and fits when you cut out that Plenum area that are fed by the two vents in front of the windshield, which are blank over.) and uses a Sanden compressor off the motor just as the +twos were outfitted from the distributorship in New York when the last of the +twos came in, so I already had all the engine brackets. But I wrote a lot about it under my name in this site, thanks, Gordon.
Hi Gordon, thanks for your comment. I found your posts in various threads - not just a/c - and will study them since my application seems similar in several respects.
Had a closer look yesterday after taking the radio out, can´t do much more just now. It seems modding the standard heater unit is quite feasible. Evaporator will go in the cold air duct which will also allow to retain the original temp. control which works well. I´d rather keep the alternator on the left and put the compressor to the right of the engine (small unit from a Smart). But there will be a lot more work before I get to that.
