3500S NADA Air Conditioning Issue.

keynsham1

keynsham1

Active Member
Some years ago I converted my NADA Air con to use R134a gas. I replaced basically the entire system and it worked as well as could be expected. I have not used the car for ages and over the years the gas pressure has dropped and the system would work but not blow cold. So today I had it recharged. The good news is that there were no leaks. Gas will eventually escape and I had lost lots. So it is now recharged and working perfectly.... except the air in the cabin is not very cold. I say it is working perfectly because the actual system is fine. It seems that I am getting hot air leaking in though at the same time. If I set the temperature to max cooling, the footwell vents still blow a small amount of hot air. I think this hot air is mixing with the cold air somewhere in the heater box which is why the air in the cabin doesn't get very cold. I have checked all the vacuum pipes and all hold a vacuum. All the flaps work and direct air where they should, except of course in the footwell when they shouldn't. I did replace the water valve a while ago with one from a Jensen Interceptor which has no capillary tube but I don't think that should have made any difference. The vacuum from the manifold seems very weak at the dash end but I don't actually know what is should feel like. I am in half a mind to just bypass the heater completely with a U pipe connecting the in and out water pipes together which should fix it but I just wondered if there were any experts out there who may have any better ideas?
 
Hi Keynsham.
Long shot from me. I do have the factory a/c in mine and assume it’s the same as “NADA units.
I had a similar problem with mine years ago.
I basically gave up trying to sort the a/c out.
I was chasing another problem later that required removing the panel that holds the two round a/c green knobs under the radio.
I noticed one of the network of rubber tubes behind these knobs had removed itself. Probably when I was fiddling for something else.
Reset that little blighter and now the a/c is back doing its best. Something to do with air pressure ,is my guess.
As an aside, I’ve been recharging the system myself with an a/c canister I purchased through my local auto retailer.
Getting a regas from a professional is quite a bit dearer.
I will get a professional regas next as there is a matter of expelling air and lube in the system which self service won’t do.
good luck with your problem
Gerald
 
I had a better look yesterday afternoon and it seems that I get heating even when the setting is at full cooling. According to the Rover manual, on full cooling you only get recirculated air from the cabin. As you turn the dial clockwise, it gradually mixes more and more outside air to the recirculated air, but no heating is supposed to happen until you get past vertical, when the water valve will start to open. I have checked all the vacuum pipes and all seems well. All the flaps work as they should. I assume that the water valve is closed in normal state and opens with vacuum so it seems to point to either it is getting vacuum when it shouldn't be, or it is stuck open and letting hot water into the heater matrix when it shouldn't be. I'll have more of an investigation later on today!
 
A couple of points, all from memory of testing my yet to be installed installation...1. The water valve is 'off' with no vacume (or holed diaphram) so no heat.
2. The outlets are either the windscreen vents and/or the face vents. no 'floor' vents
3. The inlets for the system are primarily the two shin level 'floor' vents of the standard heater only system. No air should exit from them
3.5 The top inlet in the main box is an external inlet however, despite its size, the air needs to travel past the fan motor and the main wiring and tube harness before it gets into the main inlet plenum which must seriously restrict fresh air at low car speeds.
4. The vacuuum requirements are actually very low. I found I could use a hand pump to make everything work while I watched it. A couple of pumps was enough on the main line for many actuations.

With the above in mind I'm thinking your problem may be a sealing issue. Probably between the actual unit and the body/firewall dashboard pushing hot engine bay air into the cool areas of the system. This would explain why you have mediocre cool air coming out the cabin inlets and nearly no cold air elsewhere.
 
Given the water valve completly blocks the flow you could just clamp the rubber hose with vise grips (suitably cushioned) and see if that makes a difference.
 
Problem solved...sort of! The Ranco valve has failed and does not seal when closed with no vacuum and is letting hit water flow around the heater. I started the engine and put the air con on full before the engine had a chance to warm up and it was brilliant for about five minutes and then as the engine warmed, so the air con blown air began to warm up. I drained the coolant and took the valve off. You can blow through it easily when there is no vacuum and it is supposed to be closed! So I need a replacement which is a bit annoying as the one I have is only three years old and from a Jensen Interceptor supplier. New remanufactured parts are so bad. There are loads of options in the USA for this type of valve and they are cheap too but very little choice in the UK. I might try an American car specialist and see if they can help.
 
Every now and then I do a search to find replacements for that valve. So far i've found the one you have is common with GM vehicles and the Cadillac range of similar date used the same valve as the rover - including the temperature sensor. They are also sold under the Everhot brand. I think Holden's might sell them in UK.
 
I am beginning to doubt my sanity! According to the Rover manual, for when you turn the left dial past vertical and towards the red, it says... "Modulated vacuum is applied to the water valve to admit coolant to the heat exchanger". This suggested that valve is naturally closed and opened by vacuum. The replacement I had was the other way around, so normally open and closed with vacuum, which might explain the erratic operation of my heater!! Normally closed valved seem very difficult to track down but I have found one option in the USA!
 
Quick update.... I have bought a normally closed valve from the US for £16.82 from Amazon US with free postage. I couldn't find one in the UK. I assume as my last was from a Jensen supplier that the system they have requires a normally open valve as that is what they supplied but it is not right for the Rover as var as I can tell.



Screenshot 2025-04-14 075322.jpg
 
Well the new water valve is now installed and my air con and heating are working perfectly. So there is a solution to the unobtainable original valve after all!! 20250425_150306.jpg20250425_150310.jpg
 
You must log in or register to reply here.
Back
Top