I need help identifying a component in the heating system. There are two hoses right behind the transmission dip stick. In fact they are so jammed in that its hard to check the transmission fluid level. But that's not my problem.

I have replaced one of these hoses a while ago, so I have a recollection that they are the in and out to the heater core on the other side of the fire wall inside the passenger cabin. Is that about right?

Anyway, one of these hoses has a diaphram contraption with a little rod activated mechanism that seems to pump the diaphram in and out?

I am wondering what this is and what it does. Also, could this be the cause of my heat going cold from time to time? The position of the transmission dip stick seem to be such that the lever might be getting hung up. I tried clearing the jungle a bit and for my latest ride the heat remained consistently hot. Since this seems directly connected to the heater core it seems to me to be a good candidate for the intermittent heat problem.

Bob Franklin