Air conditioner stops cooling

2000 Volvo v70
When accelerating (particularly at high speed) the air conditioner stops cooling. Until the car is turned off the AC does not cool. Dealer checked out the AC and found no problems.

Behind your dashboard is a series of vacuum-controlled damper doors that control airflow through the heater and air conditioner. When you accelerate, you lose engine vacuum and because of a vacuum leak or other ventilation control problem, Turning your car off recycles the system…Finding someone who can troubleshoot this stuff can be quite a challenge…

Try a local shop that specializes in air conditioning work.