Hey guys I have an old 98 Lesabre, and it runs and drives great. When I first got it I had to do the Vacuum line mod on the programmer to get the HVAC to blow out the face vents. That was the best $1.60 and 30 min I spent on a car

That mod still works and was done about 1.5 years ago, the ENTIRE time i have owned the car the temp blinks when I start the car, but the HVAC has always worked fine so I paid no attention to it. That is until 3 weeks ago when I had to replace my intake manifold. I disconnected the battery without turning the system to "off". I have been doing a bunch of reading online, and it seems I may have thrown the system'* sync off by doing this.

Right now my problem is this, colder air coming from the pass side then the driver’* side. When I start the car it will seem synched for a few seconds, then it will start blinking and both vents will go FULL COLD, eventually it brings the temp back up the d-side gets hotter than the p-side. I have done the following:
- gone through AT LEAST 50 on/off cycles
- Removed the 9c fuse to try to reset
- Pulled down the glove box door and watched both the upper and lower blend doors go through there whole range of movement (which they do)
- Tried to re-sync by pushing the temp full hot, then full cold a few times in a row.

Besides getting this scanned by a tech 2, which is my last resort, is there anything else I can do?? Did I miss anything??

THANKS
JOSH

Turn the HVAC off, disconnect the battery, leave it overnight, then reverse the process. Might not do anything, but worth a shot. Make sure the HVAC is off when you disconnect the battery.

Did you try moving the rod to the blend door on the upper actuator to see if it could be moved with moderate force? That would indicate the gear inside the actuator has cracked allowing it to slip on the axle. There are pictures and fixes mentioned on the web including fixing by gluing the gear to the hub.

Also, the flashing may be from another error found rather than lack of synchronization. I have wondered if mine flashes as a low freon indicator. Since I have a 95 programmer box in my 98, I am not sure it'* totally compatible so I just watch the flashing. But I did do the R/R and glue the gear. So far it'* lasted a year.

Another note is that if I understand the system'* operation, the unit checks to see if it can lower and/or raise the temperature. That may be why yours goes to cold: it may be trying to recalibrate.