Vent blows cold/hot

[klmgb]

Strange problem, when I set my heater controls to hot, the vent will blow hot air as long as I maintain a good engine rpm (2400) as the engine rpm drops the air coming out of the vents will get cooler. The engine temp will be good and remain steady throughout this problem. I suspect may be some type of vacuum leak, but I'm not sure. Any help/ideas would be appreciated.

 

[shadetree]

Yes, you have a problem with losing vacuum. It can be anywhere in the system from a cracked/broken hose, hose has become disconnected, etc. There is a vacuum storage unit somewhere in the system. On earlier units, it is a round black ball by the passenger side hood hinge on the firewall. I had one cust unit where the pipe from the ball to the hose had cracked, and was hanging off the side.shady