OK. Sounds like nothing obvious there. It sounds like multiple situations have occurred. This can be tricky even for experienced techs. Let's try and figure out the front first. I have a couple of questions for clarity.
Can you hear the a/c compressor come on?
Is the air from the front defroster vents cold?
Is this unit automatic or manual a/c? (Does is display a temp with LED's or does it have dials, respectively?)
If it does come on, how many seconds or minutes does the clutch stay engaged?
If the air is cold can you move the rear blend door manually and get the rear a/c to blow cold?
This is to verify the ac is working and how well. If the front a/c is not very cold the best you can do is to get the modes operating properly. A shop would have to put freon in it to make it cold.
If you have vacuum present on the vacuum harness connector at the back of the front control head (either black or white line, can't remember which), try inserting a small plastic or rubber line and jump to the other lines (red, blue, yellow) and note the changes. If you can get the air to flow from the other vents then the front control head is probably bad. I have replaced a few.
FYI- The (Cold Engine Lockout Switch) valve in the coolant line does sound like it is working properly. See this page for explanation. Different design-same idea.
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I can only point you in a direction. If I could fix them via the internet I would make a killing