Does the Erg vacuum solenoid cause the ac switching from vents to defrost

It could be a vent vacuum solenoid or a vacuum problem, the selector switch is vacuum run and depending on its position put a vacuum on a different solenoid

The "mode" actuators on this vehicle are vacuum motors. So you've got a bad actuator or a vacuum leak in one of the lines.

COULD BE BLOWER MOTOR OR RESISTER

This is due to a vacuum issue. The vacuum created by the motor is used to operate the actuators that control the direction of the air flow. When you accelerate you are creating more vacuum which in turn creates more in the actuators causing them to pull harder so therefore the desired setting is changed. Check your Pcv valve and make sure your hoses aren't dry rotted or leaking elsewhere, which may impact overall vehicle performance. Hope this help explain what's going on

You defroster may not be block the vent controls that switches vent position is vacuum controlled there is a hose from the intake manifold that goes under the dash to control the vent position,you may find a broken hose under the hood on the passenger side it a long palstic vacuum hose these have tendency to break just use a vacuum tube to repair it.

either no vacuum is getting to the vent door switch or the vent door switch is bad, but I suspect the vac hose is diconnected, or cracked. under the hood the line goes into the dash to work the doors, make sure its got vacuum to it when engine is running., or there is a vac leak

There is a vacuum leak under the hood. Find the vacuum line on the passenger side where it comes through the firewall and follow it to the engine. You system needs vacuum to operate and without it the default setting is on defrost for safety reasons.

The problem is probably a faulty diverter door actuator or vacuum problem at the HVAC plenum under the dash. This is a common problem - see YouTube for help diagnosing this:
https://www.youtube.com/watch?v=Nlt9A1sp-4U

Check the vacuum hose going to the heater control valve,it may have popped off. If that is on. check the vacuum hose going to your recirculation door under the right side of your dash. I hope this helps.

check for a vacuum line that has fallen off the diaphram vacuum "switch can" near the vent shift lever at the heater box under the dash passenger side