I need help figuring out a problem with my HVAC system. Here are the symptoms:
Up until a couple days ago the AC worked great. Starting today, it is stuck in "heat" mode and blows out very hot air regardless of the thermostat setting. I can move the temperature slider from it's coldest to it's hottest setting and I can't tell a material difference in the temperature of the air coming out. Also when I push the "Auto" button, it chooses the floor vents for the air supply rather than the dash vents. While I have not checked the refrigerant pressures, the low side lines on the compressor are very cold and the H side very hot, which coupled with normal looking and sounding compressor / clutch operation suggest the compressor is functioning just fine.
I'm working on two theories right now:
1) something is wrong in the HVAC controls/ buttons such that the controls think they are set for max heat regardless of where I slide the temperature controls.
or
2) the heater valve is stuck open so that even when the system is pushing refrigerant through the evaporator behind the dash, it's also pushing coolant through the heater and heating the air after the AC cools it (I do this often on purpose when defrosting the windows).
Any other ideas? Or ideas on how to most quickly diagnose which of these is the culprit? I might be able to find HVAC controls from another car that I know is working and swap that part in so I can see if new controls correct the problem, but I'm hoping for an easier solution (and a cheaper one since buying new controls won't be cheap).
If it matters, it's a 1997 HDJ81, but I think the HVAC controls are the same and the system certainly functions the same way, though I'm sure a few part numbers differ.
Up until a couple days ago the AC worked great. Starting today, it is stuck in "heat" mode and blows out very hot air regardless of the thermostat setting. I can move the temperature slider from it's coldest to it's hottest setting and I can't tell a material difference in the temperature of the air coming out. Also when I push the "Auto" button, it chooses the floor vents for the air supply rather than the dash vents. While I have not checked the refrigerant pressures, the low side lines on the compressor are very cold and the H side very hot, which coupled with normal looking and sounding compressor / clutch operation suggest the compressor is functioning just fine.
I'm working on two theories right now:
1) something is wrong in the HVAC controls/ buttons such that the controls think they are set for max heat regardless of where I slide the temperature controls.
or
2) the heater valve is stuck open so that even when the system is pushing refrigerant through the evaporator behind the dash, it's also pushing coolant through the heater and heating the air after the AC cools it (I do this often on purpose when defrosting the windows).
Any other ideas? Or ideas on how to most quickly diagnose which of these is the culprit? I might be able to find HVAC controls from another car that I know is working and swap that part in so I can see if new controls correct the problem, but I'm hoping for an easier solution (and a cheaper one since buying new controls won't be cheap).
If it matters, it's a 1997 HDJ81, but I think the HVAC controls are the same and the system certainly functions the same way, though I'm sure a few part numbers differ.