I have a 80K 99 Q45 (pampered) The heater and defrost works fine the first 30 minutes of driving from a cold start, but then the air flow stops even though the fan remains on high. I can hear the fan running. It gets cold in the car with only a slight amount of heated air moving as the fan runs on high. We shut the car off and go inside for a meal, come back and the HVAC works great for 20 minutes then you hear the change and again loose heat/def. What is going on ?

to NICO!

There should be a self diagnostic in the factory service manual that will allow you to see if there are any obvious issues with a sensor or actuator motor... that's where I would start. You can download it at http://www.infinitiservicemanual.com

Good luck!

Heath

I went thru test and everything was OK. Ran scan nothing, no codes also. Works great for 30-40 miles, then I hear a change in the air flow and it quits both heat and defrost.

Thank you !

Q451990 wrote: to NICO!

There should be a self diagnostic in the factory service manual that will allow you to see if there are any obvious issues with a sensor or actuator motor... that's where I would start. You can download it at http://www.infinitiservicemanual.com

Good luck!

Heath

It sure sounds like a mix door actuator doing something weird. What if you turn the car off and right back on - does it stay broken? Could you run the self diagnostic while it's messing up and maybe get a code then?

It seems to me to be the mix door also. I hear the strain on the blower when things are screwing up. Because the cabin gets cold the climate control kicks the blower into high. I shut off the automatic control and go to manual low fan and then we really freeze in the cabin. This happens when we take off for Dallas which is 65 miles. Around home it works perfect. The last two trips to Dallas it did this. We were going to a play and in a ice storm and needed heat and defrost. Stupid a** thing quit as we got to the Dallas county line. Ice was freezing to the windshield. Grrrrrrrr. I thought when we left maybe we should take our old 83 300SD, and I should have. I will drive the Q around home here locally and see if I can get it to act stupid and go to my mechanic and have him check codes. So far not a code or idiot light. And what's with all this ice and snow, it was spring here now it looks like the frozen tundra outside and snow in the forecast all week.

Q451990 wrote:It sure sounds like a mix door actuator doing something weird. What if you turn the car off and right back on - does it stay broken? Could you run the self diagnostic while it's messing up and maybe get a code then?

Longshot here,but free to test and rule out........

On my old 300zxturbo,the evaporator would some times freeze up and block all airflow from reaching the vents- if you are running in defrost mode,the A/C system compressor is running,and if your evaporator is indeed freezing up,it will block air from reaching the vents,even when set on "hot". To rule this out,run the heat in "economy" mode only, NO drefrost or "auto" mode-this will ensure the compressor remains OFF and therefor a problematic evaporator can be ruled out.

Your explanation of the system blowing fine for 10-20 minutes then air blocking is exactly the same symptoms that I had when the evaporator froze up,exactly.

You know I think you're onto something. I have been running defrost constantly because of the weather. When we left the restaurant the other night I saw a big puddle of water under the car and thought it weird. I was thinking can't be the A/C draining since it's 28 degrees outside, but it was exactly where it drains in the summer. Then in the garage there was another puddle of plain water that morning. We have never had a problem with this car until this. I have the FSM and did the checks myself and everything showed good. THANK YOU for getting back to me I really appreciate it !

The evaporator has a sensor that should detect a freeze up and turn off the compressor before you get to "ice block" - but it's still worth checking out.

Heath

pweroptions wrote: We have never had a problem with this car until this.

Impressive! 16 years, and no problems--that's '90s Japanese engineering for ya.
OK, sounds like qship 96 called it, I have a few related thoughts:
if your R-134 system is slightly low, the evap can run colder than freezing and might be frosting because of it.
extreme ambient low temps may play a part.
I believe defrost mode will always run the compressor.
you might modulate between defrost auto and floor/chest econ mode as a stop gap.
Heath may also be onto a bad sensor on your evap.
suggest a full hard pump down of the R-134 system, add 1 oz of PAG-46, change your drier (just because after 16 years), and refill with the prescribed 750grams of R-134.

I want to say my Q45 feels like it just broke in. It has been the lowest cost luxury sport sedan I've ever owned. I drove to Dallas today (still winter) and kicked the HVAC into ECON at 83 and had good heat with airflow alternating between upper vents with floor heat 100% of the time. Fan adjust itself down to low all the while the upper vents have airflow come and go. So this works. I have seen puddles of water this winter from the evap. drain. I will heed all advice regarding the a/c maintenance. It's having the rack and pinion replaced with a rebuilt this week. It just started leaking onto ex .pipes. I've replaced warped rotors and leaking valve cover gaskets. Those are the ONLY issues in 16 YEARS. I have been very impressed with the car. I continue to enjoy driving it all these years later. THANK YOU all for the help !