If you see bubbles exiting the LP Teflon lines to the pump, then the most common reason for this is a leak at the LP fittings either entering or exiting the degasser (drawing air in). The plastic fittings often loosen up over time or are installed incorrectly resulting in leaks.
Another common reason for seeing air bubbles in the outlet lines is due to an inadequate purge of the degasser. As noted, the internal volume of EACH vacuum chamber is huge (they all were "back in the day"). You should purge each chamber with 3x volume of fresh liquid each day before using, to flush them of gas which has diffused back into the LP lines overnight (Teflon is VERY porous, that is why it is used for degassing!).
Still, it is certainly possible that your G1303A degasser is worn out, damaged or broken. They require full service every five years and since these were first introduced in 1994, most are very, very old and in poor overall condition. The vacuum tubing, vacuum pump, vacuum valve and 4-channel vacuum chamber module all deteriorate over time and require replacement or repair. Internal vacuum tubing should be replaced every five years with high purity, chemical rated vacuum tubing. The vacuum pump and valve usually last 5-10 years max and gradually become contaminated over time. They should be fully serviced or replaced at regular intervals. The vacuum chamber module will loose its seal over time and requires professional cleaning, resealing and diagnostic testing to determine if it can be re-used.
There are two different versions of this degasser. Most examples should see the system reach initial vacuum and stabilize within 2 minutes of turn-on. Within about 3-4 cycles it should reach setpoint and stabilize. The pump should then be heard cycling on/off every few minutes (depending on liquid inside). If they do not stabilize within 5 minutes, the error LED usually lights up and the system will require professional service. If your version only has the Power and Monitor LED's (no "error" LED), then the Monitor LED should light up quickly and stay ON all of the time the degasser is running.
Most HP 1050 degasser modules can be repaired for a reasonable cost,
but we generally recommend discarding them (esp. when contaminated or more than one vac chamber is damaged). This is because they waste tremendous amounts of solvent (due to daily flushing) and you can purchase far superior refurbished degasser modules (i.e. G1322A) which are more reliable, waste less solvent, repair parts are available, and a G1303A is very heavy vs an 18 # G1322A.
For more information on professional HPLC degasser repair, please refer to this link:
http://www.chiralizer.com/hplc-degasser-repair.html