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Hi, hope I dont upset anyone, but I have just bought a Disco 96' (serpentine belt 3.9) immaculate with 90,000klm on the clock. Drove it from Sydney back to Melbourne on the weekend, and noticed that the heaters dont seem to put out much heat. But! I have a Highline '87 fitted with the same engine, also a Vogue LSE again also with the same engine (Redemtion?). I'm wondering about the Vacuum valve on the heater hose (just on one hose) on the top of the engine which seems to run a vacuum line to the front outlet on the bottom of the plenum. I'm wondering if this may be faulty? Does it work, that when you start the engine the vacuum OPENS the valve to allow the water into the heater? I notice that the heater works better whilst under power, with the heat output reducing once you are idling along in traffic to almost non existent. Temp gauge stays in the right spot, doesnt seem to fluctuate. Should I disconnect the vacuum line, or try and simulate by tying the vacuum in the suction posy to see if it makes any difference? When you start the engine what should I see happeneing with this valve? or is a heater flush the go? any ideas?

cheers,

Now with 3 landrovers!!!!! yay!
 

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Hi Andy,
Please post how you get on with this. I'm trying to re-install the heater on my soft dash as all the pipework/valve/solenoid had been stripped out by the previous owner and I can't find out what's supposed to happen to the vacuum hose on the engine side of the solenoid. The workshop manuals don't show where it's connected and Microcat shows a vacuum tank. I guess this vacuum tank may be needed and could explain the problem you're having. Without a tank/reservoir the amount of vacuum from the plenum will vary according to revs and this would vary the amount the water valve is open. If you could post some photos of the current set-up that might help someone figure it out.
Cheers
Simon
 

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Discussion Starter #4
Hi Simon.
I ended up using a Zip/Cable tie to keep the valve arm pulled in (to simulate full vacuum), and once again the heaters are now working fine. Didnt even have to flush the core out. I also for good measure put in a new thermostat. I havent come across it (this vacuum tap unit on the hoses) before, but I think it has something to do with the airconditioning unit possibly, whereby it reduces the hot flow into the heater unit, helping to allow the cooler air to stay cool as it passes through the heater/cooler core to the ducts. Anyway, it seems to do the job, and if you put the temperature controls around to cold, it works also. I'll have to wait till it warms up here, then try the airconditioner with the unit tied in, or left to the vacuum. If it doesnt seem to make any difference, I'll probably remove it. I did see the tap units on ebay (US) pretty cheap if you wanted to try a new unit. Both of my Rangies dont have this unit on them, just straight hoses, and they work fine. I havent had a good look for the Vacuum tank, unless its in an obvious spot, it may have been removed by one of the previous owners. I'll post any future findings. (maybe not with the word Disco in it though................hehehe)

cheers
 

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1995-2002 Range Rover P38A
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Sounds like you're battling a partially decommisioned A/C recirc vent flap control. This could effect fresh air inducted into the cabin and across your heater core.

Here's a cut and paste of an earlier write up I posted for a member working on some A/C problems. Maybe it'll help...

"Have you checked the recirc vent flap function? (the flap is electo switch vacuum motor actuated and closes the outside air vent when the selector switch is in the A/C position and the fan on) The electro vacuum switch is buried in a tough spot to access (but not impossible) in the dash. The vacuum supply comes from a vacuum hose off the manifold, through a check valve, to a vacuum reservoir (funky black ball near the ignition coil) then on to a vaccum hose penetrating the firewall and on into the vacuum electro actuator switch... ... yeah, there's a lot of places for this to leak, and if it's not working properly large quantities of fresh, hot, outside air are being dumped into the vehicle when moving forward. The check valve (missing/removed in many vehicles) insures the vent stays shut when at idle and low manifold vacuum. Worth a good look over."
 

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rtkraken -- Thank You,

This information was very useful to me today (aka what the heck is that black ball, at first I thought it was the abs accumulator). The vacuum hose was severely frayed running between the manifold and the vacuum reservoir. I am planning to replace the hose tomorrow and will fit a check valve in there also if I can get a hold of one. The hole was so large in it that frankly I am surprised that the engine was running as well as it did. The journey continues, shall I also spray some carb cleaner about the engine while running and see what else I can find? The cruise control vac hoses are completely destroyed, would this also cause a vac leak or only if I tried to engage CC via a button?
 

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1995-2002 Range Rover P38A
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Glad to hear you're making progress. The cruise control has a seperate vacuum pump system and isn't connected to manifold vacuum. Carb cleaner works, but be careful. :wink:
 
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