Your Hakko Desoldering Tool may create a slight pressure at the nozzle instead of a vacuum if the valve plate in the pump head does not seat properly during motor operation. This can be caused by a degraded valve plate, or debris in the pump head.
With the unit off and unplugged from a power source, you can remove the cover from the unit and expose the pump head(s). Using the appropriate screwdriver, remove the top of the pump head to expose the valve plate cover. Remove the two remaining screws and you should see the Valve plate , You can clean the valve plate with a soft cloth and solvent ( IPA) . Inspect the valve plate for any damage/cracking and re-seat the valve plate. Re-attach the pump head making sure not to pinch off the valve plate and to secure the screws in a pattern to ensure the pump head seats as evenly as possible. Replace the cover before you test the unit.
If your Hakko Desoldering Tool uses compressed air to create the vacuum, the problem may be the solenoid valve/venturi. This valve/venturi can be removed from the unit and placed in a cleaning agent. Be sure the valve/venturi is dry before re-installing it into the unit, and be sure to inspect it for damage and for free motion. Once installed, replace the cover before you test the unit.
If in either case the problem is not solved to your satisfaction, please contact our Customer Support Department and request a case be opened to return your unit for service.