Thread: D4 a/c not cooling

Originally Posted by BradC

Generally a low high side and high low side would indicate a compressor that isn't compressing.

I presume these readings are taken while the compressor is operating?

Could be faulty or unloaded.

Or the internal high pressure relief valve has opened,but i don't think they use them in auto air compressors?

Like Brad said,moisture generally blocks off the TX,and can cause other issues.
Very often if the dryer is blocked,a temperature TD is evident across the dryer,even frost maybe seen on the downstream side.(of the drier).
And low side pressures are very low.The high side maybe high,or it could be lower than normal,as the Compressor is doing no work,depending on the system characteristics.

How have you tested the pressures?

There's only one real way to test them, which is at the service valves. The low side is between the evap and the compressor and the high side is between the dryer and the txv in the same block as the high side pressure sensor. There are no service valves on the compressor on these (unlike my old volvos which made diagnostics a doddle).

That means that a blocked dryer could cause the high side to be low. The flow diagrams that I looked at didn't identify the service valve locations and I assumed that the valves were on the compressor inlet and outlets.

Originally Posted by Graeme

That means that a blocked dryer could cause the high side to be low. The flow diagrams that I looked at didn't identify the service valve locations and I assumed that the valves were on the compressor inlet and outlets.

They aren't. If you have a look under the bonnet, the high side valve is on the passenger side adjacent the battery box in the pipework between the condenser/dryer and the bulkhead where it passes through to the TXV (which is somewhere inside the dashboard. Pretty much the point they started with and then built the car around).

That sounds familiar. The vehicle is at my son's.

Originally Posted by Graeme

That means that a blocked dryer could cause the high side to be low. The flow diagrams that I looked at didn't identify the service valve locations and I assumed that the valves were on the compressor inlet and outlets.

Correct,i was assuming at the compressor as well.
When it is running is there any Temp difference on the inlet and outlet pipes of the drier.If so that is a sure indication it is partially blocked.
If not it can still be partially blocked,surprisingly.

Only the temperature of the pipes at the valves was checked, where one might have been slightly cooler than ambient.