Larry:

If the heater hose is hot up by the firewall, the monovalve is leaking OR the pushbotton control unit is out to get you.

Try clamping off the heater hose and check vent temp -- if OK now it's the monovalve. I suppose you could rig up a power connection direct to the valve to see if the valve itself is bad or the PBCU isn't giving you enough juice.

I suspect it's not leaking enough to do anything more than raise the vent temp a bit -- the heater core is behind the evaporator, so the coolant leaving the core will be fairly cool.

I think I finally got all the leaks fixed on the TE (of the ill fated evaporator change) -- the o-rings on the compressor manifold high side eroded out, dumping yet another charge (and tons of oil this time). I re-sealed the compressor and put new spring plates in since I didn't find the bad o-rings until I put it back together (it eas fun!).

Naturally, the rear muffler fell of on the test drive....

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!