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Author Topic: Amp draw on roof air  (Read 2883 times)
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« on: October 23, 2009, 09:24:00 AM »

In sept. I took a trip in 90 degree weather.  Using my roof airs (1300)  My breakers tripped a couple times. 
I was wondering how many amps they should draw on start up and then running? I Have two of them on separate  20 AMP breakers.
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« Reply #1 on: October 23, 2009, 09:48:59 AM »

Are you runner then going down the road? If so how big of a generator do you have?

GM PD4106-1689 8V71TA  V730
Mount Holly,NC
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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Nick & Michelle Badame

« Reply #2 on: October 23, 2009, 10:34:46 AM »

Hi JL,

Alot of factors come into play with the amp draw.

First, a new 13.500 btu unit at 85 degs ambiant, will draw 30 amps momentarily then drop down to 13 to 14 amps.

Now, the factors that come into play are outside temps,[add 2 amps per every 5 degrees above 85] and blockage of the

condencer and evaporator coils. Both need to be clean and free of obstructions.

If you are driving down the road while running your roof airs, then that will also cause improper airflow across the condencer coil

resulting in overheating/high amp draw.

Hope this helps

Whatever it takes!-GITIT DONE! 
Commercial Refrigeration- Ice machines- Heating & Air/ Atlantic Custom Coach Inc.
Master Mason- Cannon Lodge #104
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MCI 1995 DL3, DD S60, Allison B500.

« Reply #3 on: October 23, 2009, 10:36:54 AM »

Ours takes about 20 amps each. Each one is on a separate 20 amp circuit. Five roof airs equals right around 100 amps (not continues, but surge). We have a 20 kw generator. 80 amps each leg; 160 total (wired for 220VAC).

God bless,


Nick and my post's just crossed. Nick is much more informed then I am. I am simply stating what we have, and what works for us (what I think we have, anyways. the 20 amp breakers have worked for us, but that don't mean much. we have 15K dometic penguin's)


Sold - MCI 1995 DL3. DD S60 with a Allison B500.
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« Reply #4 on: October 23, 2009, 12:56:20 PM »

There is a device that you wire into the "start up circuit" of both of your AC units.  It prevents a AC unit from going from fan to start-up compressor ....IF....the other AC unit is starting up.  Mine flash to @20 amps at start-up but they run at 12.5 amps seemingly without regard of ambient.  Equipped with the "control", my max draw would be 12.5 + 20 for 32.5. worst case.  So, to run two AC units you need a 4KW gen at the least.  This makes sense to me(I know.scary thought) but it is "their" numbers so don't beat me up.


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« Reply #5 on: October 23, 2009, 01:58:14 PM »

Since my only A/C are the roof airs-here's what I've had to do. One-make sure that the wire connection to the circuit breaker (all of them) are nice and snug.  I had a breaker keep popping, and found all it needed was to be tightened up for a better connection.  Two-since there is more heat in the bus when driving then when stopped, I installed a computer type cooling fan in the breaker box cabinet.  With these two things done, I haven't had a circuit breaker pop, and was in 108 degree weather this summer.  Good Luck, TomC

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #6 on: October 23, 2009, 04:27:59 PM »

While they may not be great or stand up to a lot of use, the dreaded Harbor Freight has several clamp meters that would give you an idea of what things use, current wise. 


The most costly one is $20 bucks.  Whether the peak hold function would capture start up surge, I have no clue.  The old analog one I have has been very handy over the years.

Don 4107 Eastern Washington
1975 MCI 5B
1966 GM PD 4107 for sale
1968 GMC Carpenter
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MC8 under construction

« Reply #7 on: October 23, 2009, 06:10:41 PM »

I run my front AC from a 4000 watt inverter while driving down the road.  I used to have the breaker trip occasionally however as previously mentioned I ( in separate posts )  I used an ammeter to check the draw at start up and while running ( it went over the 20 amps it is wired for momentarily and settled in at about 12 ) and then I checked all my connections ( subpanel inverter main panel etc ) And I have not had any problems since. Take note that some breakers are weaker if they have been used as a switch or have been abused by over current or are not properly seated just some things to check.



If it won't go FORCE it ---- if it breaks it needed to be replaced anyway
Albuquerque, NM   MC8 L10 Cummins ZF
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