Last night I kept running ideas through my head of what could be causing our full heat issue in the 951. While the CCU and vacuum solenoid seemed like obvious candidates, I have never really seen one fail like this. This morning before I headed to the office, I started testing the units. The vacuum solenoids seemed to operate just fine, but why wasn’t I getting any vaccum? I checked all the lines in the engine bay, and while many of them needed to be replaced, they were still pulling vacuum at the various connectors I pulled off.
I traced all the vacuum lines under the dash and they were all going where they needed to. After testing the vacuum solenoid I thought…hmmm I wonder if it is even getting vaccum to the feed port. Pulled off the line and found out it was not. I shoved a vacuum gauge with a long hose on the port and started playing with things in the engine bay. This way I could immediately see any change on the gauge without having to crawl under the dash (doing so with a giant fire extinguisher mounted to the front seat is not so easy!) No change on the gauge no matter what I messed with. So I checked the engine bay side of the firewall figuring there had to be a crack in the line or split and it was not creating vaccum. (This line is really easy to get to….if you have miniature hands. Pulled the line, it had plenty of vacuum. Ok, so only one thing left….the port that connects one side of the firewall to the other. Here you can see the two lines at the firewall. One is the feed line and one is the output line.
With the top port disconnected, I tried to shine a flashlight through it. Looked clogged I thought. No way, nothing can get in there and just clog it all of a sudden…….WAY
Uh…..yes it can. Shoved a dental pick through the port, hooked it back up to the engine side and bam, we had vacuum.
Reinstalled everything and finally the heater control valve is operating like it should! The devil I tell you.
This is one of those cases where you just have to start at one end and start testing things to the other end. Somewhere in between you will find what you are looking for, it just may take awhile. Kind of like finding an electrical short, lol.