Heat/AC not blowing -- ONLY ON LONG TRIPS

[denrainwater]

I've searched pretty extensively and found several posts that are ALMOST the same as my problem -- but not quite...

 

My '96 LS400 runs very well and is well maintained.  But I've noticed that when I go on a long trip (two hours or more -- it usually takes quite a bit more than that), my heat or A/C airflow fades and eventually quits blowing.  It's not a coolant level issue -- it does the same with A/C as with heat.  Different RPMs don't make a difference either.  In order to get the control back, the car has to sit for a period of time (sometimes stopping for lunch will make it 'all better', and sometimes it requires an over-night stop. 

Just driving around my normal daily life, it never happens -- so of course, I can never get it to my mechanic while it's acting up because I have to be several hours from home before the problem ever shows up!

It would be my guess that the problem is located in a control that directs an airflow 'door' somewhere.  When the problem occurs, you can hear the fan running as normal (responding aurally to manual adjustments in fan-speed).  But the air quits flowing from ANY of the vents.  The air always comes from the correct ports (defrost, face, feet) when it IS flowing.  But when the problem surfaces, the air-flow simply tapers off to nothing.  

It's really maddening since this car is my preferred driver, and it's BEAUTIFUL for long trips -- except for this!  If it's during the need for A/C, it's merely an inconvenience, as I don't mind driving with  my windows down for a while.  But when it's cold out (like on our trip home from our daughter's place more than three hours away last night), it can become a hazard, since I have no way to provide ANY airflow to the windshield, and keeping the windows from fogging up can become very challenging.  (Especially with two adults and two dogs, like I had last night...)

Anyone else every experience this?  With winter here, I really need to find a way to address this.  But since I can never experience the problem except when I'm a few hundred miles from home, it's never practical to get it to my mechanic to examine things while it's acting up!

Thanks in advance for any advice or shared experience...
Dennis

[billydpowell]

find out where your cabin filter is and CHANGE it....  behind the glove compartment.

[denrainwater]

Thank you for that suggestion Billy -- but I keep that changed regularly, so I'm afraid that's not it....  

[billydpowell]

well, back when I had a 95,96,or 97 one of them did that to me/us after traveling about 200 miles, just completely quit (AC) 

when I got home I changed mine and it never done it again, so, I thought that was it.. I have had 12 LS400 (usually 2 at a time for wife & me) and it has never happened again..

 

[denrainwater]

Well Billy, that certainly COULD have been the problem if it wasn't something I keep ahead of...  That is one of those 'hidden' problems that folks often don't even realize CAN become a problem.  So I sincerely appreciate your pointing that out.