Thread: DIY air con/heater in engine bay (County 110)

Running the evaporator before the heater core is pretty standard procedure. That way you can chill and dehumidify the incoming air before heating it. This makes windscreen demisting super quick in winter.

sounds like a good idea, there is a definite shortcoming fitting the tdi type ac as it limits footwell room for the passenger

I gather Puma heaters work well but earlier ones are renowned for often not delivering as much heat as desired. Am sure you could find a better element to build a heater around.


I started trying to modify my standard defender heater but after some components were accidentally damaged when it was out, finished up making one using a smaller copper/ brass/ solder core from I had from an XA Falcon. Works at least as well as the standard aluminium one which is too fine and has plastic header tanks. Does not have fan. Have an axial one for possible future addition. Meanwhile, is now enough extra room to cut off top of left footwell and make a new piece with top horizontal so Australian type air con evaporator can be raised to give extra foot space. I reckon while at it, could arrange the aircon plumbing setup so the whole assembly could be removed from the vehicle without undoing any hoses and letting gas out. Would be handy being able to get any aircon component that causes accessibility problems to other repair jobs out of the way.


Re having the heater element heating air after it goes through the AC evaporator as bee utey suggests, good idea but not sure if there is a practicable way of doing this on a Defender. Especially as the heating water circuit on a 300Tdi Defender has no tap to turn it off. Seems to me this circuit from rear of motor is important to engine cooling function. I have noticed reports of overheating damage usually occurring first around No 4 cylinder. Think maybe a better priority is having heater element acting as an extra radiator in summer but with air coming out of it not going into cab.

Originally Posted by mox

Re having the heater element heating air after it goes through the AC evaporator as bee utey suggests, good idea but not sure if there is a practicable way of doing this on a Defender. Especially as the heating water circuit on a 300Tdi Defender has no tap to turn it off. Seems to me this circuit from rear of motor is important to engine cooling function. I have noticed reports of overheating damage usually occurring first around No 4 cylinder. Think maybe a better priority is having heater element acting as an extra radiator in summer but with air coming out of it not going into cab.

There is a common type of heater valve that has four hose connections and when off allows full bypass flow without the heater. They were used on the '94 V8 RRC, Commodore VS to VY V6 (16mm hoses) and some V8 Falcons (19mm hoses). They have a vacuum actuator which can be operated either by a vac solenoid or a cable after removing the vac pot.

Does anyone know the dimensions of a Disco heater core?

Might be worth a trip to one of the self serve wreckers and measuring up some parts.

I am thinking of getting the evaporator out of the air con and heater assembly. The assembly is made of low plastic that cracks easily because of the heat in the engine bay.

I tried many times repairing it but never succeeded in totally isolating it, which resulted in hot air getting in it and heated the cold air drown from the evaporator.
This is why the evaporator was placed inside the cabin on the next models.

Ultimately the best option would be to place the evaporator inside the cabin and the condenser outside the engine bay.

I have finished verifying and upgrading the car's cooling system, the leaking 3 rows copper radiator was replaced by a new 4 rows copper type (it has been fabricated since I wasn't able to source an aluminum unit)
The leaking and clogged heater was replaced in the process.

A VDO temperature sender and gauge was installed and the fan clutch was also replaced.

I will be working on the heater/aircon assembly, I am thinking of covering it with fiberglass, only the heater and the fan will go inside it.

I will post a thread on this subject once I finish the task.

Was there much insulation in the plastic housing? Or perhaps none because yours is a Defender in cabin type? Obviously having the evaporator in the engine bay will require insulation. I have wondered if that was part of the problem with the original County one.

BTW, in light of bee_utey's comment, I'll definitely put them in-line now. Much simpler.