Blend Door Actuator

[gunrac]

94' Cheyenne. Waiting for the rain to pass to check this latest issue hoping to maybe catch a tip before starting. I know my Blend Door Actuator is bad, it makes the common thumping noise when starting and shutting off IGN for 5 seconds or so. I've put the replacement/repair on the back burner some time ago learning to live w/it. Never really thought it to be a priority issue.
Yesterday when I turned on defrost the engine began to "surge" on the road, w/fan motor high and even when it was shut down, nearly stalling the engine at a stop lite. I hit the off button, everything is back to normal. Truck has AC, but I have the wiring disconnected. Another back burner issue. I've used the heater a few times since my valve job, w/no issues.
Any ideas?

[Irish_Alley]

i also have a 94 cheyenne with the 4.3. had the blender door problem but it never caused a surge issue. but with defrost the ac is supposed to kick on and without it on i would imagine its still trying to compensate for a ac on situation and i know on mine the ac seams to really kill the engine. but does you CEL come on?

[LTZ C20]

In case you didn't know, when you turn the defrost on, the ecm changes the fuel trims and idle for the engine, so even with the ac compressor unplugged, the computer is trying to compensate for a load that isn't there, so it's just adding fuel and air for an engine speed that doesn't need the extra mixture. Turning it off, sets the ecm back to normal.

[gunrac]

Curiosity got me......went out in the rain. The AC was plugged in. Went ahead an unplugged it.....all good. What I did noticed was if I unplugged the clutch side of AC and left the back plug in, I got a little higher idol. I may leave it plugged in an see how it works out.....