I have a 99 blazer with a bit of a problem. When I turn the control **** to floor vent, I get heat out of my dash vents. I had this problem once before and changer the vacuum actuator and it worked fine for about two months. Now its back to doing this. I would like to find the reason why and fix it 100%. Any advice would be great. Thanks

 

It is possible that you have a leak in the control module that is not supplying sufficient vacuum to the actuator. A new actuator likely moves more freely than one that has been in service.

If you have a 4wd, the other possibility is that you have transmission fluid in the vacuum lines. This can be caused by a faulty vacuum switch in the transfer case.

 

I did have a faulty vacuum switch in the transfer case when I took it to the dealier the first time. They charged me about $350 to change a $30 switch I could have done my self, only if I knew it was bad. Since it went bad it sucked tranny fluid through the lines. When I got it back I still didnt have air comeing out my defroster vents. So I decided to change the actuator my self to save money, also when I had it apart I blew air through the lines to get most of the tranny fluid out. It worked great for like 2 months. Now its back to being broke. The same actuator I changed. I have a brand new control know the dealer also installed. Im wondering if there was still tranny fluid in the lines that I couldent get out. Or maybe the tranny switch broke??? Also is there a place where I can buy the vacuum lines that run to all the actuators? And is there a way to check that tranny switch to see if its working like it should. Thank you

 

Transmission fluid in the lines is a royal pain to clean out. You almost have to use a cleaner to get it out and get it out of ALL lines and components as it can migrate around the system.

Does your 4wd work? When you pull vacuum line connections (anywhere), does transmission fluid come out?

 

Yes my 4 wheel drive works. When I pull vac lines nothing comes out. I think its just the lil bit of tranny fluid that was left in the lines that are screwing thing up. Any good ideas on how to get the tranny fluid out besides buying new lines??? I have BIGGER fish to fry now. I put a fuel pump in 3 weeks agao and its not starting. First things first. It needs to start to check vac lines. So when thats figured out Ill try your ideas on how to clean the lines of tranny fluid. Thanks a bunch

 

Cleaning the lines out can be a challenge. Typically, you have to use a cleaner and force it through. Problem is that most cleaners that work good will harm the lines. I have used a stiff mixture of simple green (50/50 with water), a small plastic syringe, and my air compressor to clean lines out in the past. Put enough simple green in the line to make it come out the other end. Let it sit for a bit to emulsify the oil and then blow it out with the air compressor. Leave the line disconnected on both ends and come back in an hour or so and blow through it again. If no more moisture comes out, you are done with that line and it can be reconnected. If moisture still comes out, then it needs to dry more.