In budgeting time and money for a house I just purchased, the inspector noted that the central air conditioner is mounted outside without a pad underneath. The unit is a Carrier 38CKC024330, manufactured in 1999. The product data I found online lists using a unit riser (a.k.a. pad) as 'Recommended.'

I live in the Midwestern United States, which enjoys high humidity and harsh winters. I'm not sure how good the drainage is in the area of the unit, but it is mostly sheltered by the eave of the roof.

AC unit

No pad

Given the age of the unit -- both how it may be nearing end of life, and how it has survived this long like this -- is it worth installing a pad underneath? Are there alternative techniques, say digging out a perimeter around the unit and filling it with gravel?

  • 1
    Not worth it at this point. The most I would consider would be slipping mini-pads (8" x 8" or 12" x 12") under each of the four legs. But any manipulation of the unit would flex the copper refrigerant lines and could lead to a leak. Sep 3, 2018 at 15:21
  • Any possibility that there is a slab but it has gotten covered by much etc.? Sep 4, 2018 at 1:15
  • @DaveInCaz I suppose I could check when we close on the house (in October), but the height of soil around the unit is constant so I doubt it. However, there are a few other head-scratching decisions made in the upkeep of the house, so I won't rule it out. Sep 4, 2018 at 11:51
  • I agree, probably unlikely, but I've seem some weird things at my place too! Best of luck Sep 4, 2018 at 11:52
  • DO NOT TOUCH. - it's freaking 20 years old, yo.
    – Mazura
    Oct 8, 2019 at 20:01

3 Answers 3


Most units require a pad when installed . at the age of the unit I would probably not try to put a pad underneath as this may create a leak. In 99 the common refrigerant was R22 and the cost of a recharge if a leak is created may cost close to $1k as r22 is being phased out and local shops in my area charge 100 per pound.gravel around the unit could keep grass or weeds from growing close to the condenser coil but at this age I would not want to move it but want to keep it clean so it will last as long as possible.


In Florida we call them hurricane slabs. I have been in air conditioning industry for 25 years. I believe a slab (what ever anyone wants to call them) is a good idea. They can help keep the bottom of the condenser from rusting out. But only install on a new system at this time. Don't try to have someone left unit to install, it may cause damage to the unit. It could be rusted out by now. You have a old system, get an installer to replace it. You have a 2 ton system.

  • 2
    And when replacing it, don't let them try to talk you into a larger system unless the one you have is unable to keep the house cool (or was, before it broke). Larger systems are lucrative to sell because they cost more and have higher margins, but they will fail to dehumidify properly by running very short duty cycles. Sep 4, 2018 at 1:53

You can buy a plastic pad mold and make your own pads. Whenever you need a pad you can simply fill the mold with concrete and wire mesh and make one. The pads or slabs can be used to support air conditioners or generators.

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