super928

My AC system doesn't cool properly. The rear unit is cooling but the front is not. I changed the heater valve and there was no improvement. Next I went on to change the drier and both expansion valves. The rear is still cooling but not the front unit. Any suggestions?

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Bilal928S4

Make sure you are getting vacuum at the heater valve and it is closing.

Kevin in Atlanta

Sounds like your compressor is working. But, you can check that the pipes going into the expansion block in front of the windshield should be too hot to touch and those post expansion block should be frosty cold.

Default position of heater valve is open. Upon start-up the valve should close. The signal to close the valve comes from the setting motor on the left side of the center console. You can visually verify the setting motor arm is moving with a bit of physical contortion while turning the key on.

Assuming your car is 86.5 - 89 you should hear the recirculating flap close when you start the car - yet another way to check system vacuum. Although that could just mean you recirc pod is knackered.

If the heater valve is not closing I would start by verifying vacuum starting at the heater valve using a vacuum tester.

Wally has a pretty thorough write-up on the 928 Specialists website in Tips/Links section. Required reading for 928 owners.

griffiths

Expansion valve; Kevin is saying the small pipe going to the TEV from the drier should be warm to hot to touch, while the larger pipe exiting the TEV going back to the compressor should be sweating or frosty.

A blocked Expansion valve (debris or ice inside; poor evacuation) can give you the same symptoms at the vents.

There are plenty tips here including a quick check easy check on the Air Recirculation Flap:
http://www.nichols.nu/cat05.htm