I have thought quite a bit about whether or not to make a contribution to this topic.

The very first thing I would say is that I completely disagree with Lorne as to the reason why hot air continues to circulate when the heater knob is turned completely anti-clockwise.

The heater knob can be very stiff to turn and this does not help. One of the first maintenance tasks to perform is to remove the dash and make sure that the heater knob quadrant is clean of dried grease and dirt amd adjust it so that it is free to turn. The quadrant acts on a semi-rigid wire cable (a bit like the old choke cables) and operates a flap in the heater box which controls the passage of air. It is important that the cable outer is adjusted so that the flap can be fully closed. When fully closed no air should be passing over the heater radiator and all the air entering the cabin should be cool (?) outside air. The flap proportionally controls the path of hot or cool air. The heater radiator and the aircon radiator (technically called the evaporator) are not in the same internal compartment of the airbox. 

In reality there is a design error which allows hot engine bay air to enter the airbox. The foam rubber sealing strip which surrounds the top of the airbox and seals the airbox to the underside of the bonnets is left open for an inch or so on either side of the hinge. This leaves a large opening for the ingress of hot engine bay air. My solution may be seen at here and here

Regarding a cut-off valve for the heater I do have some disagreement on this. The idea per se is not bad however if you have airconditioning you may want to have a combination of hot air and air dehumidified by the action of the airconditioner. This is nice to have on a wet cold day when you get into the car with damp clothing and the whole of the inside of the car starts to fog up.

In order to have both a cutoff valve and heat when required a system could be set up with an electric solenoid valve and a microswitch setup to function together with the heater knob quadrant. This is probably not really necessary if the heater control flap is closing correctly.

OK. Now I will move on to the airconditioning system. To my mind, at least with the Plus 4, there are several design issues, some of which are easilly addressed and others not.

Firstly the aircon compressor is fitted to the wrong side of the engine. In order to reduce the run of the pipes the alternator should have been swapped to the right hand side of the engine (kits are available) and the aircon compressor fitted to the left hand side. This would shorten the run of the tubes but above all whould have removed the need to run a tube through the hot air zone behind the radiator. On my car some of the tubes running to the separate aircon radiater, mounted forward of the engine radiator, are excessivly long. Also the factory fitted very little insulation to the tubes, something which I have rectified where possible.

Now, inside the cabin, the design of the Morgan almost dictates that the air outlets are in the footwells. I have considered several solutions to pipe air to, or just under, the dash but I have not really found a solution.

Regarding condensate from the aircon entering the cabin there are two issues. There are drain tubes from the bottom of the in-cabin part of the airbox. If these are squeezed (or blocked) at some point condensed water will accumulate in the bottom of the box and leak or spray out into the footwells. Note that this can only happen when the aircon is running: the heater radiator can not condense water out of the air, the laws of physics will not allow it. If you are getting water entering the footwells when you do not have aircon running you must look for another source.

The second point of ingress of water is from above. There are two spiggots from the right hand side of the airbox, in the engine bay and above the righthand footwell. These may be partly hidden by the aluminium cover over the ECU. The lower one, in particular, drains condensate, and perhaps any other water that enters the airbox, but it is not fitted with a drain tube. Water and condensate can flow across the top of the footwell and throgh cable grommets.  My solution was to cut a 45° piece off the end of the spiggot and fit a drain tube. (I will try to post a photo tomorrow) The other thing that I did was to fit a thin self-adhesive neoprene gasket to the flanges of the ECU cover.

I hope this helps to clarify how the ventilation box, with or without air conditioning, functions.

Last edited by Gambalunga; 07/01/24 09:12 PM.
Peter

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