I think I have a couple problems that have all come together at once. I'll try and make this short. Truck is '05 F350 diesel. I have the single zone auto climate control (digital). Coming home from a trip the other day I noticed that I couldn't adjust the heat setting.Only have 90 deg hot heat. All vents work as far as being able to switch from defrost, floor, face ect. The fan works from low to high also just 90 deg heat comes out at each setting. I lived with the full heat a couple days after getting home and then came the "low brake fluid" idiot light on in the dash. Checked the fluid and it was full. Did some research and vacuum leak popped up a couple times in my reading. I've had my front hubs disconnected for a couple years now from the vacuum pump as they were leaking at the hubs. I check the rubber cap(plug) I had put on the vaccum line and it had deteriorated. Replaced with another rubber cap and "low brake fluid" light went out. Now...I've been hearing a clicking noise for about a month(before I left on my trip) behind the glove box.I bought a new temp actuator for the blend door. The old one was def bad as the gears had stripped out. Put new one in and the same thing is happening. Hot air only. I pulled actuator back out to see if I could see it turning while adjusting air from 60-90deg. It only moves once or twice in 5-7 cycles I adjust. The temp control valve (@ engine inline passenger side) isn't working either. If I manually pull it forward and zip tie I do get AC in the cab. Anyone ever had a vacuum pump that's worked intermittently ?? If I remember correctly the vacuum pump would come on every time I turned key on and to actual start<<could be wrong. I've done both the other day... it was on and running one time then not on the next. I'm lost...Any help would be greatly appreciated.

 

That controls the flow of warm coolant into the cab heater core. If shut then no flow which is great for the AC days though not for cold days.

Sounds like you have a vacuum leak some place, on an aged truck all you can do is break it down and re-assemble with new. Dish soap in a spray might find a leak of you pressurized the system a little bit but that could be more work than it is worth.

 

I understand what your saying about the control valve on passenger side. I know I'm either not getting vacuum there or the valve itself is bad. I do get AC like I said when I manually moving it. I'm not really familiar with this whole vacuum system. I know the line that goes to the hubs (I capped off). I know the line that goes to the T valve. I see the little gray line that goes into the cab and behind the glove box. I see a lil black box (On pass. fender beside pump)that has a couple small lines ..they are all tight. Does the blend door and temp valve work in concert with each other? Or does that temp valve only know...heat pushed to rear..AC pushed to front??
What I'm not understanding is ...if I can switch all the vents (floor,face,feet,defrost) then I assume I have vacuum or at least vacuum at that sec of switching. The only thing that makes vacuum on this truck is the lil black pump on pass. fender correct?