If everything works on the roof top unit; all the power is on and the lights dim when the compressor kicks in, so do you think it needs to be rechaged?

if the grinder just hums then it is a 240 volt unit and will burn out on 110 volts
the garage power should be the same as the house 240 v
but if only 110 v that indicates that it is 1/3 of a 3 phase power supply
if it has just started then get a electrician in to check the reason for the power drop

A no cooling problem could be anything from no power, to a bad compressor. For us to give you good advice you need to tell us everything the unit is doing. Do you hear the compressor kicking on? Do you have lights in the unit? Did you unplug, let stand for awhile and then plug back in? Is the fans working in the freezer and by the compressor? Anything and everything is important for us to know.

You need to get a reading on the current draw of the compressor. Use a clamp on ampmeter to do this. Compare your reading with the data plate on the compressor. Your compressor may be getting ready to go out. You can also check the capacitor. If may be getting weak and need replacing. Another idea may be to install a hard start capacitor if the compressor is OK.

These are a closed system.(meaning that there is no fill valves for recharging) But a heating & cooling technician can solder them on and re-charge the system. Only problem there is to get an estimate up front, and compare it to buying a new roof unit which also comes with a new warranty, as well as keep in mind that the freon went somewhere, so there is an obvious leak that will need to be addressed as well. Most times it's wiser and cheaper in long run just to buy a new roof unit.
Are you sure that the compressor is kicking in? Did anyone remove cover on roof and check lines from compressor to see if any cooling is occurring?
These don't often leak, that's why I'm asking. Any idea how old the unit is?
Perhaps in fairly new, it's a warranty issue.

The humming noise and dimming of the lights is an indication something in the outdoor unit is locked up or has failed.

Check the capacitor as it may have gone bad. If the capacitor is good, then you either have a failed motor, a failed compressor, or both.

To start with, if it's plugged in to a 15 amp breaker, and extension cord, the compressor starting up may just be enough to trip the breaker. It will draw close to 15 amps on start-up of compressor, and if there is a light extension cord used to plug it in, that only makes it worse. Make sure you shut all other breakers off in panel except AC, and try it. If you have water heater on hydro, fridge on hydro, and then try to start AC compressor, you'll be way over the 15 amps, especially if it's a light extension cord.
Keep in mind, in order for fridge to work, you need 12 volts DC (Battery) power going to back of fridge. If the controls aren't lighting up at top, you've most likely got no 12 Volt DC power going to fridge. Check all fuses as well.

You will need 12 vdc (battery or converter) for controls to work, and 115 VAC (hydro) for fan & compressor to work. With your fan obviously working, that tells me you have both already but compressor may not be kicking in. Do you hear a "moaning" sound or see lights dim when switched to cool?

No Cooling.
Turn the selector switch to “Cool” and the
thermostat to a low temperature (below room temperature).
The fan runs OK, but the unit does not cool. When the unit
housing is removed, we observe that the compressor does not
run; however, it periodically hums for 15 to 30 seconds.

Possible Causes- Check all of this before buying a new unit, that may not be the solution.

“The voltage could be low – ”
a) Check the voltage between #1 on the
overload switch and the “R” terminal of the
compressor while it is not humming. This
voltage must be 115 volts domestic USA
models or 240 volts export/overseas models.
No less than minus 10% is allowable.
b) Check the voltage from “C” or “R” of the
compressor while it is humming (trying to
start). The latter reading will probably be
lower, but it still must be 103.5 volts
minimum domestic USA or 216 volts
minimum export/overseas models.
If the first reading is above 103.5V domestic USA and
the second is under 103.5V domestic USA, there is
too much voltage drop in the lines - a situation which
must be corrected for the air conditioner to perform
safely and satisfactorily.
2. “A capacitor could be shorted, weak or open.”
Turn the power off.
Caution – There is always a chance that a capacitor is
holding a residual charge, so before touching a
terminal, discharge the capacitor as explained earlier
in this booklet.
Remove capacitors, visually examine them and test
them per instructions given in earlier section on
capacitor testing (See page 9).
If the capacitors test OK, replace them and carefully
reconnect the wires. Be sure the wires are connected
to the right terminals.
3. “Start relay contacts could be open – ” if so equipped.
Turn off all power, then check for continuity with
ohm meter between terminals 1 & 2.
4. “Compressor start winding could be open or
grounded.”
Check compressor windings per instructions. See the
section on the compressors (See page 8).
5. “Compressor could be mechanically stuck.”
This very rarely occurs and when it does, it is usually
after a lengthy shutdown. This should be considered
only after all the above possible causes have been
positively eliminated. To free a stuck compressor, use
your hermetic analyzer according to the
manufacturers instructions.

First of all, Shut off power to A/C unit. !! Next,You need to remove the filter /cover ceiling assy, and with a flashlight, look way up inside and you'll see the cooling fins etc, that look similar to the back of the AC on the roof. If they appear dusty/dirty, then they need to be cleaned. I use a shop vac with a couple of extra extensions to reach, and duct tape a pot scrubber brush (half round or round with nylon bristles) to the extension. Then start as high as you can get on the fins, and come straight down, kind of like combing the fins, but not pressing super ******* them. Move over, and down again, until you get them all, or at least as much as you can. (Thats basically the same as your return air at home) I use the nylon scrubber because the brush attachment with vacuum is usually softer bristles, and doesn't get in there as well. If yours does, great.Make sure you wash out your foam filter in a little dish soap & water before you put inside cover/filter back up. Now to the best part, The upper unit on the roof. You need to remove the plastic cover, by removing the 4 screws holding it on, or if it's dometic type, screws all around near the bottom of the cover, and lift it off. The front of the colemans have a lip that the cover is down over, so you may have to pull cover forward & up, then it should all lift up & off. Here's a spot to be real careful, and ready for wasps & bees. Very few, if any that I've done over the years, haven't had a bees or wasps nest under them, so if you can do it on a cloudy day, or at least be ready to move quick, and have a wasp blaster spray with you, it may be smart. Just don't forget your on a roof when you start moving !! Another thing to remember too, is that the roof can be very slippery when wet, or dew is on it, so watch out!! Be careful !! Now with cover off, look at the fins on back of the unit, and clean those the same way, or spray with a garden hose, and soft brush, and clean them up. Next, look at the opposite side of those coils/fins, where the fan blade is in front of it, and lightly wash it down as best as you can with the hose, spray nozzle, and a brush if possible. Remember when using brush, up & down as much as possible, to avoid bending the fins over. If you can't brush it , just spray it as good as you can, to clean it. Water should not enter trailer, unless maybe if you go overboard with spray, and pressure. If you have access to an air-line to use up on the roof, that's good to, but a lot of times, the water will wash it down better. This will more than likely cure your problem, if you get it cleaned out. At the RV resort where I work as a Technician, we usually have a flat rate of approx. $50 CDN. for me to do it for you. 95% of the time it cures the early cut-out of compressor, and people actually report it cools better than it has for a couple of seasons. It has to be clean to do it's job properly. When those areas are dirty, the upper unit (compressor etc) has to work so hard to cool, it overheats & cuts out, until compressor cools down a bit, then comes back on, until it heats up too much again, and kicks out again. That's why it doesn't do it as much in cooler times, because compressor doesn't get as hot. Your also shortening the life of your unit too.