Hi All,

My 1990 L98 is giving me problems. My AC stopped working. It started with the AC working, then it would stop blowing cold air and blow hot. I would have to stop the engine, restart and then it would blow cold again, but now that does'nt work anymore. It blows only hot air now even though the compressor is running and the AC pipes are cold. It appears there is a stuck valve or a vacuum door not opening / closing. The dash controls appear to be working andthe codestells me that the temp door range is 00 when it is suppose to be 100 to 200. I tried to locate the heater shut of valve to stop the flow of hot water, but can't find it. Even with the system completely off I still get some hot air blowing on me. Help I'm roasting!![:@]

 

On my 85 the heater control valve is located under the hood on the passengers side. The valve is located between the AC evaporator core box and the blower housing. The valve is in-line on one of the two heater hoses that gothrough the firewall with a vacuum line connected to it. Your 90 may be different.

 

I have a '89 and the samething happen to mine. The failure in mine is a discontinued
AC Delco part called the temp door actuator. It is located in the dash on the passenger
side. Drop the bottom assess panel out and you will see a computer module held
in place by 2 screws, drop it out of the way. and behind it the actuator.It has a pivot arm
on top that is suppose to open a door that blends warm and cold air, when it fails it closes
the door so only hot air blows. I was able to take a metal angle and attach it to hold
the door open for cold air and then in the winter I let the door close.