yodap
bill1024 and STR1D3R_2 should chime in but how many watts does the portable draw?

Hoggle
 
Also make sure the A/C is maintained since things like a dirty filter can cause it to not be as efficient. 

Delirious
I'll admit.  this post caused me to change my filters today.  lol. 

Tweaked

knightsilver
What part of Texas Tweaked, East humid or west dry Texas? Are ya using fans to move the airflow through out the house?

I'm in North Texas. North of Dallas.
 
My A/C is working fine. I'm just searching for creative ways to save money because I was just told yesterday that I'm going to have to take a pay cut as part of cost cutting measures. I bought the portable AC to use in my garage when working out or working on a project, but thought I might be able to utilize it in other creative ways.

RainStryke
I get that... I have been experiencing the same problem with work. I didn't exactly get a "pay cut" but the 5-10 hours of overtime I was getting every week is no longer allowed, my work has tripled and i'm getting responses of "It just needs to get done" when I mention I have no overtime available to make it happen. Gotta love that fear of not having a job overriding how you can respond to that kind of request.
 
Honestly, I would stick with the central air. I would go around the house and patch up leaky window seals and exterior doors... it's like 20 dollars for some weather strip. Going with a portable system long term will have unintended effects, like frustration/mental battles with the wife.

Delirious

STR1D3R_2
All things listed above, air filters and coils need to not only look clean but actually BE clean. Dirt and debris can become compacted in the coils between the fins. So even though they may actually look clean at a glance they may be plugged. When I do a service (quite a few per day), I go through the air handler end first. Air filter(s), coil inspection is going to happen even if I have to cut a hole in the plenum. I want an unobstructed view of my flashlight throughout the coil. Check the blower wheel for buildup in the cups. A 1/16 inch buildup can be a big hit on efficiency. Do a white glove test so to speak. There's more that I will skip (electrical connections, amp draws, blow out drain line and trap, signs of water in the secondary pan etc etc etc. Blower speed is also a concern. Newer systems may need a static pressure test, too much or to little air over the coil can have issues but for an older system making sure the blower speed is on max (when there's an  issue of airflow) may be key.
 
Start here. Pull the disconnect on the outdoor unit or kill the breaker < do not skip this!!!
Pop the electrical cover off and look to the top of the compartment for the fan leads. Pull the connections off the contactor and or board and capacitor (carefully). Once done, grab a cordless drill with either a 5/16 or 1/4 inch bit and remove all the top screws around the perimeter and pull the top off the unit (not the fan or shroud mounts) and set it aside. Then take all the side panels off (unless it's a cage style grille). Grab your garden hose and rinse the coil from the inside out on jet setting. Do NOT use a pressure washer!! Hit the fins straight on and try not to bend them over (its not that easy and rarely happens). Keep your eye on whats coming out and rinse the entire coil. Once yer done go get a magnet for all the screws you spilled and put everything back together. Take a pic of the wires before you pull them also.
This is very nec in sandy, dusty areas. Cotton weed is a killer up here.
 
Next, every time I hear of a system short cycling on temperature set point quickly makes me want to perform a load calc on the home. Does it really need 5 tons? Or did someone figure bigger is better? A properly sized system should run most of the day to keep up with the load.  (smaller system > less amps). That's where multistage and variable speed equipment took a leap forward in efficiency. (amps will drop as load decreases)
You can use both your systems to somewhat replicate multistage if you were to set your central to say, 76 and your portable to 72-73. Set the central system fan to "on" to keep air moving. The central will help keep the infiltration of heat and humidity (if any) down while the portable maintains what it can. Shutting a system down completely while the home is unoccupied is not a good thing either. It will work much harder to remove the heat when you return. Just like a refrigerator, you don't unplug it when you leave.
 
 

this is tweaked we are talking about here.  he can do the garden hose part but I suspect Tweaked Sr. will have to do all the technical stuff.