All - need someone to help me think through this...

So here is what is happening in my car.
1) Move bottom slider to 'AUTO' setting
2) Temp can be anywhere in band.
3) Compressor comes on - verified seeing it run as well as engine idle speed changing

Here is where it gets interesting.
4) If ambient temp is high, typically the system sets itself into what I call high output mode:
a) Center vent opens
b) Cool air comes out of center and doors
c) Recirc flap closes - colder air comes out and at a faster pace

Then after a few seconds, the recirc flap closes, then the floor flap opens so I get cool air at the floor and a little at the center vent for a while, then sometimes the heat overrides the ac altogether and it starts to just blow hot air.

Any thoughts on a sequence of events? I think I am torn between an issue with the mixing motor or still a vacuum issue.

 

As a followup, I guess it seems strange to me that the events happen almost with an 'order' to them. in other words, I would think that if the compressor cut off, the airflow itself would change (along with idle speed) and I would just get hot air through the vents at full recirc mode airflow. If the vacuum was not correct, I would think the air would stay cold (or at least cool even if the heater valve opened partially), just change its flow from the center vent to the floor vents.

Thanks all

 

What year car?

 

 

 

 

The compressor on/off doesn't affect the fan speed (except indirectly due to the idle speed increasing and giving you a bit more system volts). The compressor doesn't normally cycle on & off when you are in AC on mode. It just runs continuously - unless the evaporator freezes up or some other fault happens.

The behavior you describe may just be the comb flap activating ~normally.

The comb flap sits in front of the evaporator - when active it bypasses the heater box and feeds air directly from the evaporator to the console vents (and door vents) - without running through or around the heater box (through or around % controlled by the heater flap position). When the comb flap activates it always seems like airflow increases - it doesn't much overall - but due to the lower resistance to flow - more air goes to the console vents (and less to whatever else is open). Its possible you do also get a little more flow due to the lower overall airflow resistance (but this is a second order effect). When the bypass is not active the airflow will seem to be lower - air will circulate through the heater box, and unless you were in Max AC (temp slider fully left) then the heater core will be hot and air suddenly circulating around it will warm up (temporary blip up), and will anyway be a little warmer to your face than with the bypass mode (comb flap active). You are only supposed to get serious heating if the heater flaps are open (temp slide not at min) and if the hot water valve is on (which it shouldn't be at min temp).

You may still possibly have vacuum issues to the Recirc flap - but its more likely IMO to be the Comb flap. If your heater valve is leaking - even a little - this will be worse - even if everything else is working OK - because the heater core will always be hot when the car is warmed up.

Alan

 

 

Then if you are at Max Cold position and you get any heat over ambient - you must have malfunctioning temp controls OR a leaking water valve or a vacuum leak for the actuator for it - I'd look there. As an experiment maybe tie the water valve closed too... temporarily. The valves have been know to leak internally too... more difficult to diagnose

If the compressor does cycle off - you have a fault somewhere (low refrigerant or icing of the evaporator).

Alan