Hayward pro series sand filter does not have enough suction to operate pool cleaner. What can cause this?

Your hose either has a hole in it, at the sections at the waters surface where it is exposed to the air? Even a "Pin" hole will create the symptom you are experiencing.
Or... there is a clog in the unit itself.
It appears that you are either sucking in air, or the water flow is being blocked. The pump should pull water no problem through a vacuum hose or a suction style pool cleaner. If the pump loses prime, then "Water" flow is being restricted either physically are mixing with air.

That increase is due to the filter loading up with debris. Is the pool unusually dirty? If there is a lot of dirt and silt in the pool use the "waste" setting on your backwash valve while vacuuming.
This allows the water to bypass the filter and go directly out the waste line. Keep an eye on your water level because you will be removing water from the pool and may have to add more.

When the pump is running is water discharging from the waste pipe outlet?
If so then the selector valve that switches the pump outlet to waste, backwash, filtering etc. is faulty.

Remove the cover, put water into the basket, keep filling it even after it spills out onto the floor ... well just for a minute or two. Close the top and snug the hand screws. Make sure the water level is high enough to pump (I. E. water in the skimmers) turn on the pump. Wait up to five minutes to get suction. If nothing is happening ... I would suspect that you are having impeller trouble. You don't say what kind of pump you have ... it must come apart ... be prepared to replace the impeller and all seals that you encounter. If there is a ceramic face seal involved, try to not touch that surface with your fingers.

Let me know what happens.

Good luck in your repair.

Check your water level in the pool. Then check to be sure your skimmer weir is free to flop down to open and let water in.If not one of these you need to check plumbing connections, pump lid and "O" rings and suction valves for air leaks. Any of these will cause the problem you describe.

You have an air leak in your system somewhere. When it get's in your filter tank the water pressure compresses the bubble and when the system goes off the bubble expands and rushes back through the system and blows the skimmer lid.
Check your pump lid and "O" ring for cracks and be sure it's lubed correctly. Check the plumbing going into the pump and be sure it is tight. If you loose prime or the pump runs with a dirty basket for any leingth of time the water will overheat and shrink the plumbing to loosten it. If this is the case you will need to replumb the pumb.
These are the usual things, but it could be many others. If you open the filter it should have an internal air bleed. Check to be sure this is in good condition and sticks up into the top of the filter.
Good luck, I hope this helps.

sounds like air in the line. Make sure vacume hose is full of water before you hook it up

Try these tips. I am guessing that one of these is the reason that your pool filter is not working properly. If you try these suggestions and they don't work, let me know and I will trouble shoot with you again.
1. Check skimmer and pump strainer baskets for debris.
2. Check for restrictions in intake and discharge lines.
3. Check for air leak in intake line (indicated by bubbles returning to pool.
4. Backwash your filter.
5. Be sure Vari-Flo valve is set on “Filter” position.

I happen to have a copy of the users manual for this pool filter. These are the instructions for operating your filter.

1. Be sure correct amount of filter sand media is in tank and
that all connections have been made and are secure.
2. Depress Vari-Flo control valve handle and rotate to
BACKWASH* position. (To prevent damage to control valve
seal, always depress handle before turning.)
3. Prime and start pump according to pump instructions (be
sure all suction and return lines are open), allowing the filter
tank to fill with water.
WARNING: ALL SUCTION AND
DISCHARGE VALVES MUST BE OPEN WHEN
STARTING THE SYSTEM. FAILURE TO DO
SO COULD CAUSE SEVERE PERSONAL
INJURY.
Once water flow is steady out the waste line, run the pump for
at least 2 minutes. The initial back-washing of the filter is
recommended to remove any impurities or fine sand particles
in the sand media.
4. Turn pump off and set valve to RINSE position. Start pump
and operate until water in sight glass is clear—about 1/2 to 1
minute. Turn pump off, set valve to FILTER position and
restart pump. Your filter is now operating in the normal filter
mode, filtering particles from the pool water.
5. Adjust pool suction and return valves to achieve desired
flow. Check system and filter for water leaks and tighten
connections, bolts, nuts, as required.
6. Note the initial pressure gauge reading when the filter is
clean. (It will vary from pool to pool depending upon the
pump and general piping system). As the filter removes dirt
and impurities from the pool water, the accumulation in the
filter will cause the pressure to rise and flow to diminish.
When the pressure gauge reading is 8-10 PSI (0.55-0.69
BAR) higher than the initial "clean" pressure you noted, it is
time to backwash (clean) the filter (see BACKWASH under
Filter Control Valve Functions.)

you will be fine with the 1/2hp. The Hayward will move quite a bit of water as well. It may not move as much water as the 3/4hp but it's very close and the 1/2hp will cost a little less to operate so if anything, you may just have to run it for one additional hour per day to compensate. You will be surprised how much water a 1/2hp will move. The only issue with smaller pumps is if you have pop-up cleaner heads or a suction driven automatic cleaner such as a kreepy krauly, however, if a 3/4hp will run it, a 1/2hp will run it as well. You can install a larger motor on the super pump but it will not move more water unless you upgrade the impeller as well. Just make sure you don't use a bigger impeller than what the motor is rated for because it will strain the motor and cause it to overheat. Hope this helps.