Troubleshooting an HVAC problem and I've read through a bunch of posts but need some expert insight.

I have flushed the coolant and bled it (couple of times) according to recs. New water/heater valve on firewall and with no vacuum applied (open), outlet heater hose is hot and I've verified that coolant flows by disconnecting the outgoing heater hose and watching coolant flow on exit side. But even with this valve open and directing coolant through heater core--lukewarm air.

Inside the car, the coolant sensor on the heater core bridged (the sensor that doesn't allow operation til coolant is heated), the fans respond to inputs and I can hear and see various actuator arms moving. I can also confirm that the heater valve on firewall responds to switch operation on HVAC controls (closes when full cold commanded, opens with full heat). When in defrost is commanded, the center vent closes and defrost vents open. When heat commanded, some air from outboard dash vents and from defrost but most air comes from the footwell vents.

In short, everything seems to be working according to my understanding of the Delanair II system. Except, no heat.

So, does that mean I have a flap problem? I can see levers moving on both sides with various inputs and the vacuum actuator on left/driver side of HVAC system opens and closes with inputs.

Can someone show me how to identify the blend flap? (if thats it?) and if it a blend door problem, what kind of failure am I looking for?

thanks!

 

Sadly, Andy, it is likely to be a blocked matrix problem.
If you turn the mode switch to defrost, once the car is warmed up, you should get full hot air to the screen. If you get air redirected to the screen but it is not hot, then the matrix problem is very likely, as that shows the flaps are working.

The Great Palm, in his XJS book I seem to remember, says it is possible to remove the matrix without removing the dash and the HVAC unit from the car; but you have to cut the pipes at a certain point under the dash and rejoin the new matrix using hoses and clips.

 

Well, that’s good insight and so I decided to take a chance on cleaning.

I’ve already flushed it when I first restored the car and then again with engine swap but only used water.

I went to the store and got some CLR (calcium lime and rust remover) and mixed it up and letting it soak now.

in order to clear out any coolant in heater core I blew some air through it and got a rusty mix of crud out. Now mind you, previously I’d flushed with clean water and it was pristine coming out. So maybe, fingers crossed, this will make a dent.
pics below of muck after just air through the heater hose and core

 

Greg, YOU’RE A GENIUS! When you said plugged heater core I started thinking about the flow I saw from the hoses when I checked for flow and it seemed weak but I had nothing to compare it to. But after several times letting the CLR soak in the core, I got this stuff out.



The CLR cleaner did the trick* (*still haven’t gotten the car full hot but air in side vents was 125 degree after heater core flush.

 

Both my V12 Jags have had clogged heater cores.

What's odd to me, though, it that the 6-cylinder Jags don't seem to suffer this. I can't explain why. I've speculated that the V12's tendency of air pockets in the cooling system might play a part. I dunno.

Cheers
DD

 

Different water pumps and the coolant flows faster/slower in one vs the other? Maybe the coolant stagnates in the V12 heater and it doesn't in the 6?

That being said, I have never been short on heat when I had a V12 car. I daily drove it in winter down to -40°C and it had plenty of heat. Much more than an X300 that I later had.

 

-40c man that must be Goldilocks for the V12 !
this red 76 SII will get a 1986 HE with Mobeck EFI, electric fans by wizard, and a tremec TKX 5 speed.

 

It always started and was a dependable car for me. For RWD, surprisingly good in the winter, with proper winter tires of course. Nicely balanced, and with the limited slip it was actually decent to drive. I had a 1992 model, which has ABS, that was good in the winter too.

Jaguar really doesn't understand block heaters, it was in the lower rad hose so didn't warm the block or oil much at all.

 

My Dad, after the war and in the 1950s had a small parrafin lamp, sort of like a miner's safety lamp, but ref and very solid, that you hung under the sump and it just produced enough candle power to enable the old car to start on its no doubt pretty poor battery!

My car LOVES cold air, at anything below zero and particularly anything below 5°C (say 26°F) it turns into an absolute rocketship! Years ago on a motorway in minus 10°C going uphill, I had to back off at 150mph but it was pulling like a train still.

 

 

the pics above are of each stage of the clean and flush. the first one with the most debris is after soaking the heater core with CLR for 10 min at a time and then flushing with a hose. I did this 3-4 times. The next pics are after using a 12v pump to recirculate CLR cleaner through the core. I mixed 1 gallon of CLR to 3 gallons of warm water and flushed that through 3 times. So for future searchers, filling the heater core with CLR and then using hose to flush out is pretty effective.

 

Do you have one of those fibre optic cameras? Would be useful to put it into one of the heater pipes and see if you can see the ends of the core and see if it's really clean now.

 

That’s a fascinating idea. I would like to see if it’s possible to see a difference.