StratfordShark

Have the switch back together now so will experiment with the adjuster screws.

Leon Speed

Much obliged dr bob, I'll start a thread once I have enough time to do some diagnostics.

StratfordShark

Some progress but not a fix!

I got hold of another freeze switch from an S4 being broken. In iced water it switched open within seconds, and switched closed within seconds of withdrawing probe into air (my old switch was not opening at zero).

Installed it and got chilly air from go. Drove for about 10 minutes, still chilly. As soon as I opened throttle wide (maybe that's a clue - vacuum drop on wider throttle?) I lost the aircon and it started to blow warm. In fact it started to get pretty hot so I think I need to re-investigate the actuators and water valve which seemed ok first test.

The aircon clutch is engaged even when it's blowing hot, so i think the relay is ok and passing power to clutch.

One thing puzzled me. The switch I was sent was identical to one I removed from my car, except that it had a copper sheath slid along the prong all the way to the black cover at end of yellow tube. The copper tube covers about half the probe length.

My old probe was inserted all the way up to black cover. If you leave the copper tube on it will only go in as far as the copper tube which is too broad. It's as if the copper tube ensures the probe is inserted to correct length, but mine had no such tube on it and was inserted several inches further in consequence.

Can anyone shed any light on this. Is the tube meant to be on (I removed it to push in probe all the way)? If it is then it leaves quite a lot of probe sticking out which looks wrong.

The photo shows the tube slid onto my old switch. It's not on all the was because the probe has a kink.

StratfordShark

To answer my own question on the copper tube - looking at photos I took I think the tube is there, jsut that it's bolted in one one side next to expansion valve. I think the guy who sent me the replacement switch was too thorough and undid the little bracket as well!

WallyP

Sounds as if your heater valve is opening due to loss of vacuum.

Check the small black/blue check valve at the brake booster for open flow one way, no flow the other way.

If the check valve is good, test the vacuum actuators in the dash for leaks. There are numerous write-ups on this, including a paper on the HVAC system on our web site. (Go to Tip/Links, Wally's World, HVAC.)

StratfordShark

Thanks Wally. I'm going to do a thorough check of heater valve and actuators this weekend.

When I first got the car I checked that heater valve was holding vacuum (it was) and I wasn't losing vac at various positions of HVAC sliders when applying vac to main black line. The black/blue check valve also checked ok. At taht point I didn't check any of the individual actuator lines at the manifold.

But even then I remember thinking that the water valve seemed sluggish to respond to moving the temp slider, so there could well be a problem that I missed in initial check, but shows up when the system doesn't have me pumping a mity-vac.

I'll report back when I've done proper tests.

Leon Speed

IIRC it takes a few tries to get the probe seated all the way. Careful not to bend the probe or bend the exchanger fins.

dr bob

Adrian--

The hot water valve will always appear to be sluggish becuase it's the second element in a cascaded control strategy. Moving the temp slider causes the setting motor to move (motor and gear noise in front of and slightly below the pod when it adjusts). The target position of that setting motor is relative to ambient temp and the measured temp in the cabin vs the slider target temp. Only when the cabin is cold, outside temp is lower than target slider temp will the heater valve open. The actual direct control of the heater valve is not a modulating control but is really just on or off; It's the setting motor that directs air through or around the heater core, in conjunction with the valve opening, that give the appearance of a modulating temp control. So when all the stars are aligned with the temp slider position, the valve will open. Just not before.

WallyP

More precisely, the heater valve should be closed from 0% to 20% heat, open from 20% to 100%. It is also open anytime that the operating lever is in the DEFROST position.

It is an interesting system...

dr bob

Note that these are percents of setting motor stroke, not control head temp slider positions. It's a VERY interesting system. Mine still works as designed, in spirte of all my poking and prodding in there. So it's fairly robust too I guess.