86 Testarossa AC Issue

it blows really hot or only outside temperature?
may be less 134 input when only outside temperature?

 

Have you confirmed that the AC Condensor Fan is running at idle? Just stick your hand in front of the LH front wheel to confirm/deny if airflow from the AC Condensor Fan is there as it should be at idle on a warm/hot day with the AC on.

 

That's unfortunate -- does it feel like a lot of heat is in that airflow at idle (it should)? One other easy thing to do is have a look at the sight glass on the Dryer at idle with the AC "on" to confirm/deny if refrigerant is flowing.

 

That screen you are looking at is connected to all of human knowledge

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The TR spec for R12 (2.8 lbs) is in the OM.

 

Above the passengers feet is the hot water valve. Check to see if it is open or closed by feeling the output pipe.

 

You don't have to be fussy about that -- if hot water is (wrongly) flowing at idle with the AC "on" thru the hot water valve, both hoses of the hot water valve will be equally hot.

There is no engine RPM/chassis speed signal used by the TR HVAC system -- to be an "electrical thing", the only thing I can think of that it might be is, if your alternator is not working and the AC system is "on", the battery voltage might droop down to ~11V and that might make the AC ECU unhappy (but I don't know that that would make it unhappy for sure). Have you measured the voltage between the two battery terminal at idle, AC "on", when you are having the problem?

 

That would be a typical good value for an alternator (and a battery that has been recently discharged a bit from starting), but I wouldn't be too concerned if it was just 13V, or even the high 12s, at idle for this possible issue (of not having enough voltage to run the HVAC ECU) -- being well below 12V (at idle when the HVAC blower is running) would be a concern. Did you ever have a look at the sight glass when having the problem to confirm/deny refrigerant flow?

 

The hot water valve defaults to open, I believe that when it is grounded it closes.

 

Feeling the temperature of the hoses at the hot water valve is a good way to check its functionality/state -- hot = open; room temp = closed. Since you report that the system seems to work OK when at speed that would indicate to me that the hot water valve itself can work properly so the issue becomes is something wrongly telling it to open at idle. The way the hot water valve works electrically is:

1. The M (brown) wire should always be +12V when the key is "on".

2. When the STOP pushbutton is pressed, a relay connects the MB (brown-white) wire always to ground = energizes the hot water valve coil which holds the actual water valve inside always closed.

3. When any other of the pushbuttons is pressed, the HVAC ECU decides (based on the requested temp knob and sensor inputs) whether to put ground on the MB wire = energizes the hot water valve holding it closed, or nothing on the MB wire = hot water valve open, but it does this in a PWM (quickly on-off-on-off-etc.) way for when it wants to have less than full hot water flow.

At idle, with the AC "on", a warm cabin, and the knob set to request maximum cooling, the voltage between the M wire and the MB wire of the hot water valve should be a constant +12V (i.e., the HVAC ECU should be trying to close the hot water valve).

 

Yes, they are rebuildable, but it's also important that the coolant flow is in the right direction (matching the arrow on the valve body) -- any chance you got those hoses reversed?

My notes have the rebuild kit as:

Bosch 1147213007
BMW 64118390132
MB 0008350644

This valve is known as the "Bosch Mono Valve".

 

And you did no fiddling/repair with the heater hoses in the engine bay "While my engine was out for service"?

 

I've never heard of a compressor being flushed, only lines and evaporator/condensor. How does one get all the old incompatible oil out of there? Not a simple geometry to flush completely. Just curious what has been successfully done previously for R12/134a conversions with respect to the compressor. I suppose you could disassemble it and clean it out at the part level.