I have a 1989 Granmarquis and went I turn on the ac it works until i start driving. Thenit starts blowing from the top vent to the defroster vent. It seems to go ramdom from vent to vent. The vacuum lines are connected and I don''t see anything wrong. The only thing that remember was that I had to change the heater control valve with the aftermarket one and it hasn''t worked the same ever since.Oh before I forget it blows cold/hot/cold/hot air. Any help will be appliciated.[img]smileys/smiley4.gif[/img]

yes, it is the actuator door. this door regulates the air position and from cold to hot. it is under the dash. is this a digital temperature reader on the dash?

The actuator doors do work because i can hear them open/closed. No it isn''''t a digital temp reader. All the air vacuum lines are connect, under the dashboard and engine comp. Edited by: pdman

it probably is the whole control unit.

Since, the actuator door and the vacuum lines are functioning correct. I decided to change the heater control valve with an original one motorcraft because i had an aftermarket one on there already. After, i installed the Motorcraft heater control valve, my problem was solved. The heater control valve goes to the heater hose that goes to the firewall.Eventhough it is heavy on the pocket, sometimes it is better to install original parts. I want to thank Mr Jason Sereiko forhis suggestions and i too will try to help out as many membersas i can with my suggestions.

I am glad to see that you fixxed it.


post some pics of your car!

I am sorry about the pictures but i am having problem downloading them to the internet. I olde you one Mr J Sereiko sorry.[img]smileys/smiley19.gif[/img] Edited by: pdman

[img]uploads/pdman/2C8_P1010055.JPG[/img]I finally downloaded the heater control valve,which i replaced on my vehicle. This is the first time that i download picture on the web. So thanknow I can sent picture, which is informative to the readers.&amp ; ;nbs p;&amp ; ;nbs p;&amp ; ;nbs p;&amp ; ;nbs p; https://www.mercuryforum.com/uploads...1_P1010055.JPG Edited by: pdman

This heater control valve, would that also solve a problem where the AC works but the heat doesn''t?


We''ve inherited this car 4 months ago, and the mechanic my wife had check it out said something about the dampner maybe needing to be replaced. He seemed to imply that something would possilbly makethe acwork and not the heat or vice versa.


I find no mention of this in the Haynes that I have.

forgot to mention it''s a 1996

Yes. It is one of three things that could be causing that problem. The other two are the temperature blend door actuator and the heater core.

I had two problem, which was a vacuum leak & the heater control valve. First make sure that your vacuum lines are good. Vacuum lines are under the dash board.I have heard that sometimes people by mistakemight kick the line loose. So look under the dash board and inspectallthe lines.Also, inspect the lines that going from thefirewallfrom the motor copartment. After you have verify that the vacuum lines are in good working conditions. Then you must find out if your car has an heater control valve because my car is a 1989 MGM. Also find out if the actuator door open/closed by playing with the dash board buttons.The heater control valve only solved the heat which for the floor on my car. So concentrate on the vacuum line first,then on the actuator doors. Let me knowhow it comes out.Edited by: pdman

Ok, onewheelpeel I will try to answer your question. Question,the heater control valve, would that also solve a problem where the AC works but the heat does not. Yes, the heater control valvecontrol the heat in my car due tosometimes i did not get heat at all and their were other times that i got some heat. After, i replaced it the heat/ac works all the times. My problem was solved but first you must find out if you have one in your car.Also, if you are going to buy it buy the motorcraft one not the aftermarket one because i had thesame problem with the aftermarket one.So i hope this answer your question.[img]smileys/smiley14.gif[/img]

Is there a Factory Service Manual that I can download from somewhere for my year?

I get most of my info from the Chilton book. Whatever, info you want to know about your car is in that book. Most of the time you can pick it up at your local library, or purchase one from your auto parts store.