MikeAK Posted January 31, 2021 Share Posted January 31, 2021 Hi, After recently getting my P38 rebuilt engine running I decided it was time to fix the leaking heater O rings and and the book symbol on the HEVAC display (fault reported as RH blend motor open circuit). So out with the dash. Fiddly but not as bad as I was expecting. Unfortunately this was the state of the lower dash. Not done by me, it was like this when I removed the centre console facia. And the RH blend motor was like this. Motor and mounting bracket both smashed off the heater and the cable severed. I can only assume the PO or his garage had tried to gain access to the heater O rings by smashing through the RH side of the lower dash then gave up without changing the O rings and causing all the damage. Some people shouldn't be allowed tools! It seems the blue/green mounting bracket is not available as a separate part, but all the bits are there so hopefully I will be able to Araldite it all back together. I have a spare blend motor and a lower dash is on order from Eblag. I think this is the final piece of bodgery by the PO to sort out, but time will tell! The heater pipe retaining plate was screw was seized so I had to drill the head off. plate now sat in a jar of diesel to see if that will free the remains of the screw off. I think the heater matrix is OK but am considering changing it while I have the dash out. I haven't tried yet but it looks like the metal dash structure will stop it coming out. Does anyone know if entire heater will come out if I unbolt it? Looking at it I'm not sure it will clear the metal dash structure? Thanks Mike Quote Link to comment Share on other sites More sharing options...
Simon_CSK Posted February 3, 2021 Share Posted February 3, 2021 Mike I took the dash out of mine last year and like you didn't seem to be a big issue just time consuming. I trick I used before refitting was to put some tape on the windscreen above the bolts for the rear fixings. It gives you an indication where the bolts should be rather than trying to fish in the dark. Would suggest you get a new dash from a breaker. I had one but unfortunately my spares vehicle decided that it wanted a barbeque. Quote Link to comment Share on other sites More sharing options...
Northwards Posted February 3, 2021 Share Posted February 3, 2021 That's a horrible mess someone made. Please keep the pics coming! My P38 is 20 years old/77,000miles and I think that sooner or later I'll be in the same position to change the O rings and check all the HEVAC motors. Quote Link to comment Share on other sites More sharing options...
Escape Posted February 3, 2021 Share Posted February 3, 2021 You can get the heater matrix out by cutting the metal structure, bend it back a little and afterwards rivet back together. We dd 2 like that couple of months ago. If you need some parts for the dash, like the bracket, feel free to send me a list in a pm. I have a complete RHD dash that's waiting to go in the skip as there's no demand around here. Happy to post to help you out. Filip Quote Link to comment Share on other sites More sharing options...
Simon_CSK Posted February 4, 2021 Share Posted February 4, 2021 Filip I had the hole in the panel to allow me to change the o rings and did so before I found out that the matrix needed done. I was surprised how easy it was taking the dash out and wouldn't bother cutting a dash in future. The only issue with the dash removal is the time it takes but as my P38 is used so little it isn't really a problem. Filip I had the hole in the panel to allow me to change the o rings and did so before I found out that the matrix needed done. I was surprised how easy it was taking the dash out and wouldn't bother cutting a dash in future. The only issue with the dash removal is the time it takes but as my P38 is used so little it isn't really a problem. Quote Link to comment Share on other sites More sharing options...
MikeAK Posted February 4, 2021 Author Share Posted February 4, 2021 Thanks all for the advice. Haven't had chance to look on here for a couple of day and I pre-empted Escape's suggestion of cutting the metal bracket in front of the heater yesterday. I removed about 5mm in the middle which allowed the two ends to be wiggled out. I probably didn't need to remove any metal, just cutting it would have done I think. Thanks Escape for the kind offer of dash parts, but I had already ordered the lower dash from Ebay before seeing this. Rest of the structure and vents etc. seems OK Once that was out of the way it was easy to wiggle the heater box out leaving the AC evaporator part in the car. I made a small "repair piece" for when it goes back together. Also means future dismantling will be easier if (when) I have to do it again. Once the heater box was out I was glad I went to the trouble. The heater core is very crusty and had been leaking from the seam where the plastic end tank joins the heat exchanger. So a new one required. I then fitted the replacement blend motor and plugged the heater box in with it sat on the centre console to check everything works. It didn't! The blend flaps were OK and moved correctly. But the distribution flaps were very stiff, the motor could hardly move them and frequently stalled. So dismantled the heater box and found that several of the flaps were tight in the bores they run in. Lubricating didn't help so did some measuring and the bores were smaller than the bearing surface on the flaps! Don't know how that's happened, does plastic shrink with heat and time? So carefully drilled out bores slightly larger and everything nice and free until the heater box was full clipped back together when the flaps were binding again. Not as bad as before but still to tight for the motor. This time I found that when box was fully clipped the flaps were binding on the bosses on the central dividing wall. So I slightly sanded the bosses on the wall to relieve it slightly. Now the flaps ran freely, seems like the outer walls of the box were pressing to hard on the shafts. Again is this distortion due to age and heat? Sounds simple but that was over half a day of repeated dismantling, adjusting, re-assembly and trying! Tried it again loosely in the car and this time all the flaps calibrated using Nanocom and could be driven to any position using the diagnostics. Happy days. I should have taken some pictures but I got too involved and forgot until the box was re-assembled. however its all fairly obvious when you have the heater box apart. While I had the Nanocom connected I noticed the heater core and external ambient temperature were way off both around 95C (heater display said external temp 55C so I presume it limits at that) temperature was about 8C at the time and engine not run for a couple of days. That might explain some of the random temperatures coming out of the heater. Both sensors measured randomly varying 150K and 259K ohms with no correlation with temperature (fridge and hair dryer) so they are both duff. Heater core sensor STC3256 and Ambient sensor STC3257 both appear to be obsolete. Hardly anywhere has stock and anywhere that claims to have stock has them listed at ridiculous prices. So I connected Nanocom back up and to monitor temperature readings and resistance substitution box in place of the sensors and to get an idea of the thermistor resistance values and curves. I think I have found some suitable bead thermistors from RS/Farnell that I will have to find a way of mounting. If anyone is interested I will start a separate thread on the P38 HEVAC sensors etc. None of that stops me re-fitting the heater box and and starting to re-assemble the dash so that's tomorrows job. Mike Mike 1 Quote Link to comment Share on other sites More sharing options...
Escape Posted February 5, 2021 Share Posted February 5, 2021 12 hours ago, Simon_CSK said: Filip I had the hole in the panel to allow me to change the o rings and did so before I found out that the matrix needed done. I was surprised how easy it was taking the dash out and wouldn't bother cutting a dash in future. The only issue with the dash removal is the time it takes but as my P38 is used so little it isn't really a problem. We did a couple of dash removals when stripping cars for parts and I never found it easy. Maybe we were just unlucky, but even with good access (engine removed etc) I was a real pain, with stuff breaking and bolts/screws stripping, especially for the scuttle panel. And it takes a lot of time. Whereas by cutting the bracket I can swap a heater core in just a couple of hours. @MikeAK the flaps binding in the heater housing is a known problem. I agree it's probably distortion of the heater box due to heat cycles etc. You're the first one I know that has done such a thorough job! Congrats! Filip Quote Link to comment Share on other sites More sharing options...
MikeAK Posted February 5, 2021 Author Share Posted February 5, 2021 Started putting it back together today. Another advantage of removing the heater box is that you can clean out the years of muck and small plastic toys in the the evaporator housing and drains. Another cause of wet carpets. Putting the heater box back in. And fitting the modified bracket. Not going to do any more re-assy of the dash yet. I discovered today there is no gas in the AC system. So I want to pressurise it first to make sure there are no leaks in dash before I go any further. Thinking of putting in 20 to 30 PSI of Argon from the welder which should be clean and dry and enough to find any leaks. Need to make up an adapter tomorrow. Thermistors ordered from RS so will be having a play with them tomorrow as well. Mike Quote Link to comment Share on other sites More sharing options...
MikeAK Posted February 13, 2021 Author Share Posted February 13, 2021 I managed to get some more time on this a couple of days ago. Cobbled together an adapter to put some argon in the A/C system to pressure test it. It was leaking from the condenser faster than I could put it in! Pulled the front grill and A/C fans off and found a crack in one of the condenser tubes. Squirted a load of Araldite in and left it overnight to go off. Next day put about 50psi in it and didn't seem to leak. Left it overnight again and it was still holding pressure the next day. So I don't think there are any other leaks, just needs a new condenser. That can wait for warmer weather, don't need A/C at the moment. While waiting for the for A/C pressure test I had a play with the thermistors I bought from RS to replace the faulty heater core and ambient air temperature sensors. Both worked correctly giving correct temperature readings. I'll start a separate thread about the sensors so the information is available for anyone who needs it. So todays job was refitting the dash. Managed to get the main dash in , but still have to fit instruments, glove box and airbag. It was to cold to complete it! Couldn't work with fiddly screws with gloves on and fingers didn't work in the cold without. Either way couldn't feel and just kept dropping things. Not to much to do now though when it gets a bit warmer! Mike 2 Quote Link to comment Share on other sites More sharing options...
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