AC amp draw question/ efficiency question

cvin · 06-25-2017, 03:52 PM

Trying to decide on replacing an 1986 old RV air conditioner with a newer model for better efficiency

We have been monitoring the amps on this old air-conditioner here in southern Arizona
For several hours during the hottest part of the day it's drawing about 18 A, would the newer models be more efficient than this, or is this about normal for all of them?

It seems to cool the small camper pretty well

Any info is appreciated

Outback 325BH · 06-26-2017, 11:30 AM

Quote:

Originally Posted by cvin

Trying to decide on replacing an 1986 old RV air conditioner with a newer model for better efficiency

We have been monitoring the amps on this old air-conditioner here in southern Arizona
For several hours during the hottest part of the day it's drawing about 18 A, would the newer models be more efficient than this, or is this about normal for all of them?

It seems to cool the small camper pretty well

Any info is appreciated

I'm sure this varies among brands and models.

I have a fairly new camper (2016) and have three air conditioners: one Coleman Mach 15 and two Coleman Mach 3+.

The Mach 15 draws around 13 or 14 amps. EachMach 3+ draws around 11 amps.

Obviously the choice is yours. If the air conditioner doesn't work very well the choice is easier... but if it is working OK, whether or not it is worth it to get a new one is tough.

cvin · 06-26-2017, 12:02 PM

This is great info, right now he is leaning toward replacing it

It works but occasionally trips the breaker when the outside temp is 110-115
and we are a little concerned about stressing the old wiring in the camper also

bobbecky · 06-27-2017, 01:24 PM

If the breaker going to this unit is rated at 20 amps, the wiring should be #12 copper, and all the connections are tight, you should be fine with this unit. Sometimes older, and maybe a little less efficient is more durable than newer units. It will take a long time to make up the cost of a new unit if this one is still working, even if you are paying extra for the power.

**JRTJH** · 06-27-2017, 01:49 PM

Quote:

Originally Posted by bobbecky

If the breaker going to this unit is rated at 20 amps, the wiring should be #12 copper, and all the connections are tight, you should be fine with this unit. Sometimes older, and maybe a little less efficient is more durable than newer units. It will take a long time to make up the cost of a new unit if this one is still working, even if you are paying extra for the power.

That is my thought as well. If everything is installed correctly and operating properly, no loose connections, weak breakers, small wiring, etc then it would take a long time to recover the investment, especially when you consider the reliability/failure rate of new air conditioners. Sure, there's a 2 year warranty, but the expense of troubleshooting, reinstalling a unit, shipping the old one back, just the frustration of sleeping in a hot RV until the new one arrives from the warehouse.... All of that has to be "no cost but very high frustration potential" for the owner who swaps out a functioning "older A/C".

I don't want to take the time to do the math, but using some generalities, if you consider an "old A/C" that pulls 17 amps vs a "new A/C" that pulls 13 amps, that's a 4 amp difference. At 120 VAC, that's about 480 watts difference (for the time the compressor is operating, which is not 24 hours a day). So, considering maybe 12 hours of operation, that's 480x12=5760watts. So that's around 5.8kw a day less energy for the $600 investment. At 10 cents per kw, that's about 58 cents a day. So, it would take about 1034 days of continuous A/C use to "break even" if nothing else goes wrong with the unit in the next 3 years of constant use. Given the 4 month per year use for most A/C's, that means it would take somewhere between 9 and 12 years to see a profit.... Not a very good investment, at least the way I see it.....

cvin · 06-28-2017, 12:31 PM

Thanks for all the feedback

We have pretty much come to the same conclusion, as long as it works just roll with it

The ac and frig are on the same breaker, we put the frig on a heavy duty extension cord to a different plug on the house to lighten the load on the wiring, it seems to be helping some

Bob Landry · 07-04-2017, 03:10 PM

The 18A draw may not be that far out of line. The amp draw listing on the data plate is based on a 95 degree outside temp. Don't confuse this with the 20 degree split across the coil. For every additional 10 degrees, the compressor(being part of the overall amp draw) will draw 1 additional amp. Same applies for opposite temp change. In 85 Degree heat the compressor would draw 1 amp less. If you happen to have a dirty condenser that adds heat not removed from the compressor to the total draw.

This is not just something off the Internet. It's how Dometic instructs shop techs to check a unit for correct charge without having to tap into it.

These same parameters also apply to the new units so if you are concerned about power usage and your electric bill, replacing a working unit probably isn't going to do much for you.
Check the temp at the discharge and at the return grill and if you see a difference of 18-20 degrees, that's as good as it's going to get. When you check this, don't get hung up on how hot it is outside. That has nothing to do with inside cooling, the split across the coil does.

Looking at the original post, the unit is 31 years old. I wouldn't even spend the money to have a shop check it out, just replace it. It ill fail you when you need it the most and most shops don't have a competent A/C tech on staff anyway. They are parts replacers and a bill on a 31 YO AC can easily exceed the cost of buying new.

cvin · 07-04-2017, 07:47 PM

We added some more shade and some of that styrofoam looking insulation stuff to the roof and it seems to be doing pretty good in this 104-115 heat we have been having

I am still amazed it even thinks about working being that old and in these extreme temps

xrated · 07-05-2017, 02:16 AM

Yes, it's 31 years old but it's still working well if it does the job for you in that kind of heat. In some instances, things that were made 30 years ago were made better than their newer replacements.....and that AC unit might just be one of them.

Bob Landry · 07-06-2017, 04:19 AM

Every now and then you run into one that just won't give it up. Marine Air used Rotorex compressors from 89-91 and were so awful they stopped using them in their equipment after three years but I still occasionally run into a unit that is still running. Sometimes there's no substitute for a little dumb luck.

You may also like: