P38A Heater unit service. What's to be done?

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Bagshot

Bagshot

Well-Known Member
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866
Location
Cornwall
Reluctantly I have my dashboard out to carry out repairs to the pipework,(yes the o rings.. I know. Don't go on !). However, as it's all out, looking to do some preventative maintenance in there. So looking for advice as to what can be done whilst access is there..
Cheeers
 
Bagshot said:
Hi thanks, can the flaps be operated whilst the electrics are all off..?
Click to expand...

Just make sure they are full and free by hand after removing servos. If you remove the quadrant that operates front and rear distribution flaps make sure you reassemble it correctly. Before you remove it move it fully in both directions and note marks that MUST line up correctly in either direction.
 
wammers said:
Just make sure they are full and free by hand after removing servos. If you remove the quadrant that operates front and rear distribution flaps make sure you reassemble it correctly. Before you remove it move it fully in both directions and note marks that MUST line up correctly in either direction.
Click to expand...
Thankyou Sir, that's the sort of thing I'm looking for , anything whilst its all apart.
 
Bagshot said:
Thankyou Sir, that's the sort of thing I'm looking for , anything whilst its all apart.
Click to expand...
If the quadrant is stiff free it off or the rear distribution flaps are anything like stiff split the unit and free them lube with HMP grease. The pivots are plastic on plastic the old grease going hard causes them to stiffen up. I made a new seal top of unit to dash out of foam. Old one had disintegrated. Take out matrix and check for corrosion, if light, clean and coat with aluminium paint. If heavy replace.
 
A quick google shows the Nissens heater referred to in the link as being just over £20 on ebay so if you're taking the matrix out would it be worth just using one of those instead?
I've no idea how much work would be involved though!
 
Ratae said:
A quick google shows the Nissens heater referred to in the link as being just over £20 on ebay so if you're taking the matrix out would it be worth just using one of those instead?
I've no idea how much work would be involved though!
Click to expand...

Why?
 
Depending on the heater box version, the flaps may have rubber surrounds, or be all plastic. The latter get stuck on the box sides. Mine is the version with rubber edge flaps, so these didn't stick, but the shafts were sticking where they go through the housing. I took the box apart, and enlarged the shaft holes by about 0.5mm. Cleaned & re-greased the gears so they moved quite easily with one finger. No sticking since, and no servo errors.

I think the Audi core is worthwhile, but I had issues with the o-rings not sealing in the end of the original pipes because the fitting was damaged (probably by previous owner). I tested the original core & pipe fitting on the bench, and decided the Audi core & new hoses was the simplest solution.
 
pwood999 said:
Depending on the heater box version, the flaps may have rubber surrounds, or be all plastic. The latter get stuck on the box sides. Mine is the version with rubber edge flaps, so these didn't stick, but the shafts were sticking where they go through the housing. I took the box apart, and enlarged the shaft holes by about 0.5mm. Cleaned & re-greased the gears so they moved quite easily with one finger. No sticking since, and no servo errors.

I think the Audi core is worthwhile, but I had issues with the o-rings not sealing in the end of the original pipes because the fitting was damaged (probably by previous owner). I tested the original core & pipe fitting on the bench, and decided the Audi core & new hoses was the simplest solution.
Click to expand...

If the pipes have not been fitted correctly fully home on their location slots fitting a longer clamp plate screw is likely to damage the housing. The trick is to do the job properly in the first place.
 
Bagshot said:
Thankyou Sir, that's the sort of thing I'm looking for , anything whilst its all apart.
Click to expand...
wammers said:
If the pipes have not been fitted correctly fully home on their location slots fitting a longer clamp plate screw is likely to damage the housing. The trick is to do the job properly in the first place.
Click to expand...
Many Thanks to all here. I appreciate the thought regarding the upgrade matrix and it sounds good, but at the minute Mrs Bagshot is threatening death or divorce if I spend anything more than a £1 this time around, (some kinda holiday coming up I gather) so everything I can do through good old fashioned servicing and maintenance gives me points.. and allows me back in the house.
1) I will take the box and flaps apart as described and check the flap bearings/ shafts and seals.
2) New foam seal on the top I think I can make up from window draught excluder..(in the Dibnah shed already)
3) Clean it all out (and somebody shoot me first) but I have seen on here http://www.stockholmviews.com/p38/index.html#blend a description of taking apart the blend motors and carrying out a bit of cleaning and maintenance on them without buggering up everything. Worth a look..?
Luckily for me, I havent had any noticable heaters issues, (apart from the O ring seal) but whilst I'm this far in, I want to make the most of the access, I dont fancy going through the rip out again for a long while.
 
After you re-install the heater & new o-rings, I would do coolant pressure test if you have the kit. This should show any o-ring leaks without starting the engine. Alternatively, it is possible to fire up the engine and check for leaks before re-installing the dash, BUT you need to do some work-arounds first.
  1. Remove SRS Fuses & Relays from main fuse box. This way you will not trigger SRS faults.
  2. Connect HEVAC (Incl. sensors, flap motors, etc.)
  3. Connect Instrument cluster. Cluster is required to enable the HEVAC backlights !
  4. Check earth connections.
  5. Fire up engine and wait for warmth.
You should now be able test the HEVAC and see if the flaps move correctly for heat-cool, and direction.

If all is well, then re-fit the dash.

Last step is to enable the SRS again.
 
Bagshot said:
Many Thanks to all here. I appreciate the thought regarding the upgrade matrix and it sounds good, but at the minute Mrs Bagshot is threatening death or divorce if I spend anything more than a £1 this time around, (some kinda holiday coming up I gather) so everything I can do through good old fashioned servicing and maintenance gives me points.. and allows me back in the house.
1) I will take the box and flaps apart as described and check the flap bearings/ shafts and seals.
2) New foam seal on the top I think I can make up from window draught excluder..(in the Dibnah shed already)
3) Clean it all out (and somebody shoot me first) but I have seen on here http://www.stockholmviews.com/p38/index.html#blend a description of taking apart the blend motors and carrying out a bit of cleaning and maintenance on them without buggering up everything. Worth a look..?
Luckily for me, I havent had any noticable heaters issues, (apart from the O ring seal) but whilst I'm this far in, I want to make the most of the access, I dont fancy going through the rip out again for a long while.
Click to expand...
If you take the blend motors apart take care, if the gears fall out you will need to get it back together right.
 
Right..
Am nearly at the end today.
Heater box out and split apart, all flap bearing surfaces cleaned, old dry grease (yuk) cleaned out and new white silicon grease in place. Not a noticeable difference in movement on the levers, but then they were pretty good already. Heater matrix flushed and find vacuumed out. Some corrosion on one corner but I think that was from the O ring leak. High tech pressure tested it..hand over one hole and blow down the other in a bowl of soapy water..passed.
IMG_20181217_113517.jpg
IMG_20181217_112617.jpg
All reassembled and silicon spray on everything. Touch of grease in the gearing.
Motors opened up, no miissing teeth and pretty clean in each one, so sprayed out with some contact cleaner and silicon sprayed to death.

Everything back in, all ducting cleaned out AND..all joints gaffer taped together. Surprise how loose and floppy everything was. The joints had some dead foam in them so scraped off and used some draughed excluder to close the gaps and taped.
New foam on the top, (same stuff as above, 10mm thick) to replace the dead foam around the outlets.
IMG_20181217_131040.jpg IMG_20181217_131027.jpg
New bulbs in all the switches and HEVAC, new bulbs in the binnacle. Just ready to fire up tomorrow in daylight to check for leaks.
Phew...
 
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