Agree with @halbeezy and to add to those comments:
Obviously, 'bubbles' mean gas in the system. Could be nitrogen from failed 'globes' -- not likely with new 'globes' but residual gas in the system from old failed 'globes' may be a possibility. More likely, the source is air which, despite all efforts, has found its way into the system during the 'globe' change-out, or, has been there for a long time.
Different to the brake system, the AHC system has some areas where old fluid and air can stubbornly resist efforts to removal. It cannot be flushed by simply by passing fluid through the system. This can take a lot of persistence involving several raising and lowering cycles and many bleeding cycles, depending on how much air is trapped or entrained, and where it is located.
Happily, this situation does not happen every time bleeding is undertaken and very often the process is straightforward -- but not always.
Consider the diagrams below, for example, when air trapped in the fluid in the 'Height Control Accumulator', or, trapped far away in the 'Shock Absorbers', or, sitting in one of the longer fluid lines.
This can take a lot of effort to remove -- won't happen just by cautiously opening the bleeder valves -- it will need repeating the "PADDO Method"** multiple times, and/or adapting the method such as by the suggestion above by @halbeezy .
Persistent bubbles is one indication of such circumstances. To resolve the problem, each cycle needs to include causing the Height Control Accumulator to empty and refill multiple times, and, raising and lowering the vehicle to causing the 'Shock Absorbers' to fill then displace their contents multiple times, then bleeding each time at each of the five points, with vehicle in the "LO" position and allowing it to descend completely as each bleed point is opened.
**
replacing AHC globes/accumulators
Hi All, Just to share some new found knowledge... After driving around with bone jarring suspension for a few months, I finally got round to fixing it yesterday. The sudden tailtale drop in AHC fluid reservoir level told me the globes had finally (after 320,000km) gone. So I ordered some...
forum.ih8mud.com
AHC System Lowering -- fluid is released from 'Shock Absorbers': ECU opens the Levelling Valves in the Control Valve Assembly, fluid exits each 'Shock Absorber by passing up the internal central tube in the direction of the arrow, allowing the vehicle to lower. Pump is OFF, so the Return Valve is CLOSED and fluid passes TO the AHC Tank
AHC System Raising -- fluid is sent to 'Shock Absorbers': ECU opens Levelling Valves in the Control Valve Assembly and causes AHC Pump to operate, thereby sending fluid to the 'Shock Absorbers'. Fluid passes down the central internal tubes in the direction of the arrow, filling the 'Shock Absorber' and causing vehicle to rise. The Pump is ON, so the Return Valve is OPEN and fluid is drawn FROM the AHC Tank
It also is worth noting that air can dissolve in the AHC fluid under pressure and emerge as a gas (per Henry's Law) when the pressure drops -- such as when leaving the pressure side of the system during the bleeding process and becoming visible in the bleeding tube or container receiving the fluid, or when arriving at the AHC Tank. It is nice to save fluid but that is a secondary objective -- the main game is to be in no doubt that all air has been displaced from the system -- no bubbles in the exit stream after a long bleed. Be wary of re-using fluid unless very, very sure that it does not contain any entrained air -- and this may be difficult to see.
Various IH8MUD threads including the lead-up to Post #243 by @aharlan001 shows how frustrating this can be:
AHC Inop after fluid change 2007 lx C1751 and C1762 - https://forum.ih8mud.com/threads/ahc-inop-after-fluid-change-2007-lx-c1751-and-c1762.1233088/page-13#post-13517321
There are multiple other IH8MUD examples and their causes may be different -- and I have had my own bad experiences with remnant air in the system. The common ground is that a lot of persistence may be required to remove it.
Finally, it is worth being conscious of how and when the Height Control Accumulator operates, as set out in the FSM. The solenoid valve on the front end of the Accumulator normally is closed. It opens only when instructed by the ECU when actually raising the vehicle, or, when the Accumulator is being re-charged by the AHC Pump after a raise. This is described below and in greater detail with limitations explained in the FSM. There is little point in bleeding the Height Control Accumulator unless it is fully charged. If nothing or very little comes out, then the Accumulator is in a discharged state with nothing or very little in it.
It is possible that the Height Control Accumulator and/or its solenoid valve are faulty. That would be unusual -- and can be detected by observation and testing per FSM.
The point of all this is that if air, or fluid loaded with air, is "trapped" in the system somewhere between the six exit points (the sixth exit point is where fluid returns to the AHC Tank), it may shuffle backwards and forwards until repetition finally brings it to an exit.
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