928 S Heater control valve ?

kenthepipe · **Posted:** Tue Sep 13, 2011 6:54 pm

Has anyone replaced their heater control valve (plastic crap) with the equivilant Mercedes one Part No A000 830 5784..., It,s a hell of a lot cheaper Merc- £16..., Porsche almost £60

stratfordshark · **Posted:** Tue Sep 13, 2011 8:08 pm

I buy most of my 928 parts from USA.

Last heater valve I bought was about £14 - it's one of those parts which for reasons best known to Porsche is about 25% of UK price in the US - the official Porsche part I mean in case you are wondering.

Of course it takes longer to get hold of and you have to pay for shipping, but latter can be very modest cost by US mail, and you still save a packet if you order a bunch of parts together (and there is always a shopping list if you want to spoil your 928).

I remain a huge fan of OPCs for parts (personal experience of great service from Sutton Coldfield, Solihull and Reading for parts), but I use them when I am in a great hurry for a part and/or when the US price offers no saving over UK (true for many parts, but no rhyme or reason to it).

Sorry haven't answered your question! Is the Merc part functionally equivalent? Some water valves are designed to be shut with no vacuum, not open like the 928 part. Haven't heard of Merc equivalent but on Rennlist some people are fans of Audi valve which is metal so more durable than the Porsche part.

Do replace the short hose to block when you change the valve - common source of leaks.

kenthepipe · **Posted:** Tue Sep 13, 2011 8:39 pm

stratfordshark wrote:

I buy most of my 928 parts from USA.

Last heater valve I bought was about £14 - it's one of those parts which for reasons best known to Porsche is about 25% of UK price in the US - the official Porsche part I mean in case you are wondering....., yes I,ve seen the US and Uk prices, pure extortion !, US price around $20 to $30, which is about 1/4 the price of Uk..., over a 21 year period This will be the third valve I,ve bought.

Of course it takes longer to get hold of and you have to pay for shipping, but latter can be very modest cost by US mail, and you still save a packet if you order a bunch of parts together (and there is always a shopping list if you want to spoil your 928).........., i also get stuff from the states when I can, last thing was a tripset gearwheel, Roger T.

I remain a huge fan of OPCs for parts (personal experience of great service from Sutton Coldfield, Solihull and Reading for parts), but I use them when I am in a great hurry for a part and/or when the US price offers no saving over UK (true for many parts, but no rhyme or reason to it)........ I concur.

Sorry haven't answered your question! Is the Merc part functionally equivalent? Some water valves are designed to be shut with no vacuum, not open like the 928 part. Haven't heard of Merc equivalent but on Rennlist some people are fans of Audi valve which is metal so more durable than the Porsche part.....
The Merc part is identical,I,ve seen a picture, probably the same supplier,.... I,m waiting for further confirmation from someone who has used this part, it has the vaccum plenum as per 928 and am confirming with him about the outlet / inlet stubs, they should be 3/4inch

Do replace the short hose to block when you change the valve - common source of leaks.

I also replaced this last time, so hopefully it,s still serviceable.
The Audi one is about £30, and was fitted to the early 100,s and Quattro,s etc, of those years, unfortunately, my local Merc dealer does,nt have the valve in stock, so I would have to take a gamble and order one. So once my contact confirms,details etc, I,ll know.

Thanks for your input.

FYI..., further replies in your quoted text ? odd little site ?

stratfordshark · **Posted:** Tue Sep 13, 2011 10:39 pm

OK Ken if you are already a customer if Roger T then you need no advice from me regarding parts. He is fantastic!

kenthepipe · **Posted:** Wed Sep 14, 2011 12:06 pm

stratfordshark wrote:

OK Ken if you are already a customer if Roger T then you need no advice from me regarding parts. He is fantastic!

.., agree , a nice man to deal with!.., still waiting for some more info on the Merc valve, but as it,s i/d to a 928 and a reasonable price I might get one regardless . I,m not exactly too sure if I need one yet , but thought it possible that the valve membrane is,nt working as it should.

I recently had a new compressor and drier fitted along with vaccum out and gas re-charge, everything working great ( ice cool air ) then at the weekend the air con is only coolish.Was cold when I set out...,

then....,

I noticed after a hot run, and car stood thirty minutes, when re-started is when I noticed impaired cooling, possibly hot water escaping into heater through the valve and this then has to be cooled ??

stratfordshark · **Posted:** Wed Sep 14, 2011 12:55 pm

Hi Ken,

The valve will always allow hot water from block into matrix when the engine is switched off, as the default valve position is open with no vacuum (sensible arrangement to remove heat from block).

But even with matrix being heated, in a properly working system this shouldn't affect temp in cabin as the mixing motor will completely shut the flap where hot air is mixed with ambient.

It sounds more like you have a leak and are losing gas.

Apart from the aircon, is your hvac system working correctly? Is air cool when at full cold position with aircon off? Can you control tempertaure with slider?

kenthepipe · **Posted:** Wed Sep 14, 2011 5:48 pm

Hi Adrian..,

Started the car from stone cold today, and switched on the air-con, practically blowing ice cubes. ( No hot water in heater core ) Now last time the car was out, last weekend, it was the same, however after a run of about twenty miles, with air-con working fine the car was left standing for half an hour I noticed when I started her to return home the air-con was only marginally cool ( hot water migrating back to heater core ? ) after a while into the journey things seemed to be getting colder, but not as. ( water now being cooled eventually by air-con? )
Sliders are working fine both controlling top vents and dash centre,s. it was a member on Rennlist that told me about the Mercedes heater valve being the same part, so bearing in mind this valve is now six and a half years old, it might be a very reasonable price to pay for a Merc valve, especially as the Porsche one is almost 60 quid, as opposed to £16 for the Merc one.

I still think it might be a wise choice to replace it, just so there is,nt a weak link ? and wondering if it is, or is,nt working properly

stratfordshark · **Posted:** Wed Sep 14, 2011 7:05 pm

Always good to renew heater valve but from your description it's unlikely to be faulty.

A perfect heater valve will allow hot water into matrix when car left standing, but the system will not mix any hot air with the cooled aircon air when working correctly if a lower temperature is demanded. The cooled air does not cool the heater matrix but is fed direct to vents in cabin. If problem was warped valve you would have felt warm air on run before you let car stand as hot water would have passed through.

There are several elements in 928 system which need to be operating correctly for system to work (with or without aircon):

All 5 vacuum actuators
All 5 vacuum solenoid switches
The temp slider in controller
Cabin temp sensor
External temp sensor
Mixing flap motor
Comparator circuit in mixing motor
Hot water valve (but vac actuator included at top of list)

Best thing is to work through all of these (tests are pretty easy, and all accessible with little effort) to get evrything in tip top condition.

It could be also be as simple as the rubber seal between area ahead of windscreen and bonnet not sealing, and allowing warm engine air into blower area (would build up when car left standing)

kenthepipe · **Posted:** Wed Sep 14, 2011 7:07 pm

..., Cheer,s Adrian :wink:

kenthepipe · **Posted:** Sun Sep 18, 2011 10:19 am

Just an update.., I bought a Mercedes heater valve and it is EXACTLY the same part as the Porsche valve, £19 inc vat as opposed to £62 for the Porsche valve ( go figure).
After removing the old valve and not having a "Mityvac" I rigged it up as to how it works. I discovered that the vacuum is working, I attached a small bore vac hose to the nipple on the vacuum canister, closed the valve by hand and nipped the vac hose so that the valve was held shut. Then I filled the inlet side of the valve with water, and over a period of 40 seconds the water had drained, thus proving that the section inside was warped allowing hot water to escape. When I get a chance I,ll run her and report back..,

stratfordshark · **Posted:** Sun Sep 18, 2011 2:33 pm

Good test Ken and really interesting to hear about the Merc valve and how cheap it is.

The disc is prone to warping so do post back the result on your hvac performance. I always thought that if yhr valve allowed hot water through when it shouldn't that you would feel warm air from one area of the vent closest to the heater matrix but that performance was otherwise not badly compromised. I could be wrong though! Always learning about these cars.

kenthepipe · **Posted:** Mon Sep 19, 2011 11:42 am

..., cheer,s Adrian, I,ll update you as soon as.., :wink:

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928 S Heater control valve ?

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