I have a 1990 L98 that doesn't blow hot air until I run the temp up to 80*. I recently changed the HVAC head and my antifreeze solution is 50/50. What can I do next? Thanks

 

I hope you talking celcius

 

Do you mean you have to set the temperature to 80* or you don't get any hot air out of the heater until the coolant reaches 80*

 

You realize that 80 is hardly hot air? And you do realize your car makes heat from the water running through it, meaning warm motor = warm air?

 

Assuming it's electronic air, I wouldn't pull your hair out over it. Any Auto setting between 65 and 85 means that the Processor or Programmer is going to position the temp door based on inputs from the inside and outside temp sensors to reach and maintain the dialed in temp. You can get all a/c; all heat; or a combo of the two. I have no idea what the basic parameters or code is inside that Processor. The literature (ie Shop Manual) suggests that it's designed to reach whatever temp is set as quickly as possible based on the input from the aforementioned thermistors - take that for whatever it means. I do know that if you start out at say 78 on a 50 degree day (it doesn't get much colder than that in So. CA) after it has sat at Home Depot for an hour or two around midday - you will get killer a/c for about 10 to 15 minutes and after that a mix of a/c and heat. I've never stuck a thermometer in the vents to see what the actual temp of the air is under these conditions, but it feels fairly comfortable given the outside air temp. I can only suggest that if you want it to be warmer, bump up the settings and if you want maximum heat, set it at 90 because the Processor then ignores the temp sensors and shuts the Temp Door so that none of the air reaches the a/c evaporator - everything flows over the heater core. If that doesn't toast your toes, your heater core is probably plugged up and needs to be flushed or replaced (or the temp door isn't shutting all the way - probably because it's linkage is broken).

 

Also w/ the elec control when you disconnect the battery & first reconnect. You need to leave the heater on auto for a full 3 min. on first start up. The system is cycling the door to full stop in both directions to register things. So you might want to try that & then see what you get. It's also possible you've lost the vacuum line to the control & it isn't running the door at all??

 

There's no vacuum involved with the Temp Door - it's controlled by an electric motor that changes direction when the Programmer reverses polarity.

 

What is cabin temp when you are trying to get heat from the HVAC??

BTW, the interior air temp sensor is behind and above the driver's seat in the bow.

My '88 has that setup and had to serivece the connecting rod clip recently.

 

SunCr has the best teechnical info here.
I always like to read his 'Tech Tips'.

With that I'll throw this in....
My heater stopped working well. It would give very little heat.
I removed the hoses from the core out under the hood.
(you can get to them by the evaporator core box on the passenger side)
Reverse flushed it with my garden hose and Rube Goldberg contrapcion of heater hoses,etc.

A nasty looking bunch of 'stuff' came out of the core.
Afterwards, and since then, the heater has worked great.
That was a couple of years ago.

 

I had problems getting heat from my low mileage 96 LT4. On the input heater hose to the heater core located just under the radiator fill tank I have a plastic orfice in the line. I think it acts like a valve that restricts water flow under higher rpm's. I found the center of the orfice partially plugged by something hard but small about the size of a half of a small finger nail. Heater works fine now.

 

You still haven't confirmed if you had run the engine coolant temp up to 80* or if you had run the digits on HVAC controller to 80*.

 

With the electronic controller I think thats the way its supposed to work. My 88 wouldn't start blowing air on real cold days until the water temp hit 80*.

 

Are we talking coolant temperature or the temperature set at the Controls? Certainly a coolant temp of 80 degrees isn't going to feel real warm.