Meatful

The rear AC is really cold at any fan speed. However the front AC blows cool but only just.

• Front blower works great
• Repeatedly cleaned ductwork from dash and firewall sides
• All new vacuum lines on the engine side
• New checkvalve near brake booster
• New heater valve (x2 to make sure)
• Heat works fine
• Removed and cleaned the HVAC control panel
• Removed and cleaned the interior thermistor/blower assembly

Transitions to heat and back without issues, and verified heater valve goes full open and full close when cycling.

Why would rear AC blow a blizzard but the front is only a little cool? Mixer Flap adjustment? Does the exterior thermistor provide inputs only to the front AC mixer?

thank you.
86.5 928S AT

Kevin in Atlanta

The symptoms suggest hot water is getting past the hot water valves. In my experience the hot water valve is either closed when the car is running or open when it's not. it does not cycle.

My test is to see the front vent temps at startup. If it goes for ice cold to warm as the engine warms up you have hot coolant getting past the 2 hot water valves.

Are you sure the hot water valves are oriented in the correct direction?

And what the high and low numbers? The front expansion valve could be clogged.

Meatful

Temp stays the same hot or cold engine. Double checked orientation and tried two different valves. By cycling, I mean seeing the valve lever travel fully when changing the selector from full hot to full cold.

Expansion valve clog is an interesting thought.

Kevin in Atlanta

That's why we need to know the high and low side pressures.

Speedtoys

What does the front do without the rear running?

A COLD rear with a "meh" front with both running at the same time is sorta normal.

The stock condenser isn't large enough to run both at the same time with good results.

The Forgotten On

I'm guessing your foam on the blend doors is no longer present and/or misadjusted and some of the interior vacuum valves are leaking.

Common issues for sure.

You can check to see if the front evaporator is getting cold by sticking a thin thermometer into where the capillary tube from the freeze switch slides into it.

This would for sure tell you if it's working (expansion valve clogged or not as stated above) on the refrigerant side without having to test pressures if you're uncomfortable with doing it.

Kevin in Atlanta

I hear that a lot from other 928 owners, but here in Atlanta my 87 and 90 S4 will blow ice cubes to the point I have to turn down the fan. The latter was converted by a previous owner and still has the R12 o-rings and original AC components. Go figure.

Most of it comes from a thorough cleaning of the system using BG or something like it. But, a really good AC tech is really important.

Kevin in Atlanta

Also...

With the AC going feel the pipes at the front expansion valve. They should be ice cold and frosty going into the evaporator.

Kevin