This is a long story that I'm going to shorten. We have an 06 Discovery with the Denso AC system. It would cool OK at speed but at idle it would basically just blow ambient air.
I'm a little knowledgeable and have AC gauges and a good vacuum pump. I also have a neighbor who is much more knowledgeable. When I put the gauges on it showed OK at first then the high side pressure would climb to 450PSI or so and quit cooling. 450 is WAAAAAAY too high!
My buddy said there had to be a blockage in the system.. Talked to some folks on the Discovery forum and decided to replace the dryer. They are not expensive and it's right up front on the firewall. After pulling a vacuum and charging the system, it acted the same way. Curses!
So that leaves the expansion valve. Unfortunately the Denso system is installed before the dash and it's nearly impossible to get to it. I was able to remove some bolts and pull back the facing and gain access to the plastic box that holds the dampers, condenser, and the expansion valve. More unfortunately, there is not an obvious way to disassemble the housing without a total removal of the dashboard and removing the entire DENSO unit.
But there is always a way. Based on where the lines came through the firewall, I had a good idea where the valve was. To verify, I CAREFULLY drilled a 3/8" hole in what I expected was an empty place in the housing. Through that hole, I inserted my USB endoscope camera (handier than a hip pocket) and immediately saw the valve and the surrounding area. I then took a vibrating multitool and cut an access panel.
With some large wrenches, I was able to remove the valve and pull the sensor off it's clamp.
Replacing the valve was the reverse but reattaching the sensor to the low (cold) input pipe was a chore. There is not a lot of room at all. Finally got it done. I made an aluminum piece that covered the opening and pop riveted the part I had cut out to it. Silicone sealed up all the cracks.
Vacuumed down the system again and charged it up. ACTED THE EXACT SAME WAY! *&#$@!))
Called my buddy over and he verified things and said "Somewhere, there is a restriction". So we started at the compressor which was obviously running because we had pressure. He asked if the condenser was blocked and a light bulb went off. Up front I had my buddy fire up the coach and turn on the AC while I watched the condenser fan. Yep, fan wasn't coming on. Checked voltage to the fan and it was there when it should be. Bad fan!
When I removed the fan, the brass fitting was completely wallowed out and disengaged from the electric motor. The motor was running but the blades not turning. Advance auto parts had a 16" fan in stock. It wasn't a bolt on replacement but it was easy to adapt. Installed and everything is all better. The AC puts out 35 degree air constantly and after a 700 mile trip performed flawlessly.
One thing I learned was that an expansion valve system will not freeze up like a capillary tube or orifice system will. The temperature sensor that was such a pain to clamp to the low side input tells the valve to reduce refrigerant flow when the coil gets close to freezing.
The moral of this story is to always check the simple things first. I should have known to look at the fan but in a car, the fan running is obvious and is ALWAYS on so it's not something you even have to think about.
Lessons learned.
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