- 98inSFl wrote:
- Why does that happen? I believe the evaporator coil in the dash is divided top and bottom for the left and right(respectively) dual zone air.
When low on freon the top of the evaporator is not filled with freon as well.
All I can say with certainty is I have seen this on caddys, impalas , monte carlos , topping off the freon fixes the VENT air on the left and cold air on the right.
Anyone else have a differing theory ?
I have no theory, just answers. That would be a "no" for the '95-99 G body Riv according to the factory service manual - which probably is also why noone's yet made this particular 'low freon' observation on the '95-99 G-body Riv. To wit:
Page 1C-7 of vol 1 of the '98 G body factory service manual set shows a cutaway, 'figure 7' of the AC airflow. In the Riv, all the supply air for both passenger and driver flows through one single plenum and must all pass the evaporator, all the time.
For those who're more curious,here are some details:
* unless the "VENT" button is pushed on the HVAC control head, the A/C runs just about all the time. It does not run under heavy acceleration or when ambient outside temp is below some number. Technically speaking: the HVAC head 'requests' the AC compressor to be on in Defog, Defrost, or when the Vent button is *not* pressed. If the sensors also do not indicate that the evaporator is freezing (outside temp is above 6 deg. C) then the PCM honors the request and lets the AC compressor clutch engage (in order to keep the evap core at 1 deg. C). By The Way, this is why it can be tough to defog the windows when the outside temp is between about freezing and 42 or 43 fahrenheit and it's humid -- it's humid enough to get condensation on the insides of the windows and the outside air is above freezing and holding much humidity, but the AC is not running. Air holds much less moisture when temp is below freezing and can become super saturated at the 'triple point' just above freezing (I will save the rest for a different 'dissertation). So 42-43 degrees out on a humid day, you could have foggy windows for a few minutes. Oh, yeah... if the PCM wants to reduce engine (parasitic) load, for instance when starting the car or when driving at full throttle, it will disengage the AC compressor clutch.
* The "passenger temperature offset" basically is set up in the Riv so that the driver and passenger side air belnd doors are
side by side at the evaporator plenum. So instead of one air mix door there are 2. ( Remember - all the air flows thru the evaporator to the passenger and driver mix doors, which set side by side at the exit of the evaoprator's plenum.) Passenger can change the passenger temp control setting so that the climate control computer tilts the passenger's blend flap to run more or less air over the heater core and into the passenger side's ducts, unless the climate control computer overrides - which it will if for instance the defroster only is on. The differential bar stays lit on the passenger door control, though.
* You *can* blend air (thus getting a temp differential) to the defroster ducts, to a point, if you set the control head to blow air from both the defroster and floor vents for instance. You can measure the differential with a probe but it's not as much as in 'mid' or 'floor only' mode, which I suspect is one reason GM did not engineer temperature *numbers* in the HVAC display for this particular (G body Riviera) model.
* you may be amused to know that there are certain "purge" overrides in cold weather at startup and if the AC is on at startup, intended to blow superhumid air out of the evaporator plenum.
Hope this helps clear the air (heh).
Albertj
