It isn’t the vacume line. It’s sucking. Any idea what else it could be ?

 

You'll have suction. Just not enough to get it off defrost. I had a tiny tear in the boot here (bottom line). You won't see a tiny crack in the lines either.

 

When you have the plug off the mode selector in the dash panel, do you have vacuum on the black hose? That's the vacuum supply from the "T" on the firewall in the engine compartment. Each of the other colored hoses go to various vacuum actuators on the heater/AC unit. When you loose vacuum, all the actuators go to defrost by default. That way you'll still have heat which is critical for survival in cold climates and can still see where you are driving.

 

 

Yes when I took that off it is sucking from the black hose. No other hose though is sucking, none of the colors. Regardless if I have that thing attached or not to the back of the dial it’ll only blow out my defrosters

 

Okay, try sticking a small hose into the clear plastic piece with all the colored hoses on it while the engine is running. If you have a vacuum pump, you can use that. Into the black hose hole on the face of it. Then try putting the other end of that hose into one of the colored hose holes and see if anything underneath moves. Each of those colored hoses go to a vacuum actuator that looks like a round can with a shaft coming out of it that moves a duct door when vacuum is applied. If the actuators move by powering them one by one this way, I'd say the mode switch (dial) is leaking or blocked internally somehow.

You just proved your vacuum supply to the heater thru the firewall is good. Now you have to prove the actuators don't have broken diaphragms. That's the reason to apply vacuum to each one individually. They may be designed to function together for some modes and if one has a leak, it will bleed off the vacuum so that function doesn't work. I'm not sure, but I think there is one door that closes off the whole unit from the outside air when everything is off. If that is broken, nothing else will function except defrost.

 

So get a hose, and put one end into the hole where the black hose was sucking ? And the other end put where one of the colored hoses are that weren’t sucking ?

 

Exactly! Think electricity. The black hose is the hot wire and all the different colored hoses are the things that need to be powered up. That dial thing is actually a rotary valve that directs vacuum to different actuators.

When I talked about that door that shuts off outside air, it's like the forward clutch in an automatic transmission. If the forward clutch doesn't engage, all the other clutches don't matter, the car won't move without the forward clutch. Except maybe in reverse. Did I just confuse you more?

 

No that makes sense thank you. I will do that today and report back. Thanks a lot !

 

what was supposed to happen? I may have not understood correctly but when I put a small hose in the black one and attacked the other end to the other colored spots nothing seemed to happened. I may have done something wrong though ?

 

So I took a small straw and put half in black hose (the hose thats sucking) and other end in the colors. It did nothing. I’m not really sure what the sucking is supposed to be doing but it didn’t do anything at all when using the straw. I wasn’t completely flush but almost.

 

It ended up being the mode switch , just the dial. NO VACCUM ISSUE AT ALL.