Belt is slipping

This is likely due to a worn and slipping belt. Replacing the belt should solve the problem

If I understand the issue correctly, the belt that drives the machine's transmission squeals. When does it squeal? When engaging the clutch? When in motion?
Typically it's the condition of the belt. It's likely slipping due to stretch, wear or from an oil leak causing it to slip, or simply due to a loose idler pulley, worn idler pulley bearing, broken spring. Look for all that stuff. Look at the drive belt and inspect for wear, cracks, fraying, missing rubber, etc. Replace it if any of those conditions are found.

A slipping belt makes a loud squeaking noise when the engine is running. The belt needs to be changed if it is cracked or fraying on the side, or if it begins to slip.

check clutch for slipping condition,mayb due to worn clutch disc or a oil contaminated disc or a weak pressure plate not locking disc to flywheel therefore giving u a slipping condition and higher than normal rpms

It might just need a simple adjustment of the running belt that can eliminate the slipping refer to you owner's manual for the procedure. It will be close to all treadmill running belt adjustments.
Here is a generic procedure for adjusting the belt:
If the walking belt slips when walked on. Run the treadmill @ 3 to 4 mph, walk for a few minutes, Using the allen wrench, turn both rear roller adjustment bolts clockwise, 1/4 of a turn. Then repeat adjusting procedure until walking belt is properly tightened.

The only air conditioning component I can think of which could cause the serpentine belt to break would be the compressor. If you look under the hood you can see the belt winding around several pulleys of engine parts. The air condition compressor is the part which has two hoses with metal fittings and a wire harness attached to it. When the engine is on the pulley attached to the compressor should be rotating at the same speed as the other pulleys. Keep your hands, clothing and jewelry clear of all moving engine parts. If it is moving at the correct speed it is good, if it is not moving correctly it will cause the belt to slip creating friction until the belt breaks. Once the belt breaks the engine cooling, power steering and battery charging will stop, which will quickly cause the engine to stop working. This could cause engine damage, but it will defiantly strand you with a broken vehicle. If the pulley is working and the air conditioner is working, do not worry about it, but you may want to check the belt with the engine off for cracks or damage. If the belt is slipping and the air condition is not working, the vehicle will need a new compressor, coolant, and possibly a dryer. This could set you back about three hundred dollars. If you do not want to fix the air conditioning and the belt is not slipping run the vehicle as usual if the belt is good. If you do not want to fix the air conditioning and the belt is slipping you may be able to bypass the compressor and use a smaller belt.

As a general rule, the belt should be kept as loose as possible. However, the belt must not slip on the rollers in normal use. Possible overtension can be quickly checked by walking on the belt at a speed of 3 mph The belt must slip on the front roller if you brake the belt with your feet, holding onto the hand rails, while you walk. If the belt does not slip, the tension is too high and the rear roller must be loosened. The belt tension and alignment is done by adjusting the rear roller position with the attachment bolts at the back of the treadmill a 1/4 turn at a time until correct tension attained. T

depends upon weather, driving conditions, engine options, but the bottom line is the belt will eventually dry out, crack or start peeling (fraying) which should be visible to the naked eye. Also look for oil on belt which can make it slip.There is also an indicator (3 notches looking down from top) which indicates belt wear/stretch. replace belt if outside of indicators.

Check the clutch lever free play. It should have about 3/4 inch of movement before any resistance is felt. The speedometer problem may be a bad inner flexible shaft within the speedometer cable. Unscrew the meter end of the cable and pull out the flex shaft--it may be frayed (replace) or just need lubrication.

To tighten the belt, start by locating the two bolts that adjust the rear roller (one on each side of the unit in the back). Run the unit at about 3 mph. Tighten the bolts a 1/4 turn at a time. Make sure that what you do to one side, you MUST do to the other side or the belt will get off center. After you tighten it 1/4 turn, check the belt to see if it is still slipping. If it is then tighten the belt 1/4 turn again. Continue until the belt does not slip, but do not tighten the bolts more than 2 full turns.