AC not working

fdsparky · 08-09-2010, 02:48 PM

Our AC runs when we have plugged in to power (but not very cold), but when we switch over to generator (3500W, large enough to run AC) it runs for about 10-15 seconds and just drags the generator down. We've had it running off the generator before, but just recently it started doing this. Is it possible maybe it's low on freon?

NWJeeper · 08-09-2010, 03:23 PM

Welcome to the forums.

Air conditioners are designed to cool approximately 20 degrees from ambient. Therefore if the temperature in the rig is 90 degrees the air will be 70 degrees coming out of the AC. As the room temp cools naturally so does the ouput of the AC. The only way you can tell for sure if the AC is working right is to measure the temperature of the air coming out of it right at the grill.

You did not mention what type of generator you are using. There is a big difference in generators and the "el cheapo" ones may say they are 3500w but they are actually 3500w surge and 2500w continuous run which would likely not be enough to run your AC. The other possiblity is that the govennor on the engine may not be ramping up the RPM to adjust for the increased load of the AC and therefore will need to be looked at by a good shop.

macbwt · 08-09-2010, 04:31 PM

Your Generator may be too small to run the AC. I believe it is a 30 amp system and if you were to do the math on the amps needed you would find it is too small for the AC possibly. For example a 6500 watt generator will handle 29.5 amps of draw. This does not count the start up needs when you hit the AC on it draws even more amps just to start. I would say you just do not have enough generator and it eventually shuts down due to over amperage demands. Try borrowing or renting a 6500 watt and see if there is a difference.

NWJeeper · 08-09-2010, 09:09 PM

I might point out that many use a Honda 3000i generator to run AC units just fine. Most motorhomes will have a minimum 4000w generator unless you upgrade when ordering which is more than enough to run AC. You do not need 6500w to run AC, however like I said in my first post, not all generators are the same. Honda 3000i generators are rated for continuous duty and will have a higher surge for when the compressor starts but cheap generators will not. Your AC is most definately NOT 30 amp. The supply to the RV might be but this is because they have to account for other items running, especially the converter/charger which is always on. I have run my AC on a 20 amp outlet in our garage with the rig plugged directly into it (no extension cords).

macbwt · 08-10-2010, 03:58 AM

I would still try a larger Gen just to ensure the AC is working and rule out the Gen as the weak link. As far as motor homes my fathers Monaco Dynasty uses a three cylinder Diesel which has to push two AC's and I know that Gen is kicking out the Amps.

cardinal4fun · 08-10-2010, 07:58 AM

If your AC has run in the past on both shore power and generator and now it does not. I would check the condensing coils on the AC in fact take a hose and soft brush clean the coils. If they become clogged the unit will not work at peek performance. Also and most likely not the finns on the coils may have been bent, you may want to straighten them out, be carefull doing this. If the coils etc. look good then yes you may have to have it check out by an AC tech.

fdsparky · 08-10-2010, 10:11 AM

I appreciate the advice. We know it's not the generator because we've ran the AC plenty with the generator we have. We'll just have to keep troubleshooting. Just haven't had much time to do that right now.

LadyWindrider · 08-10-2010, 10:34 AM

Since no one else has asked, I will. What size AC, and what size generator, and what outside temp, and what altitude??? All engines loose performance at heat and altitude. While your generator may be fine at lower elevation, or cooler temps, it may not be enough for peak heat or warmer temps. Also your AC draws more current at higher outside temps, due to working with higher pressures in the system, the compressor needs more amps. Don't be too fast to say the generator is fine. A Honda or Yamaha may run the AC when it is 80 outside, but will struggle when it is 100. Give us the AC size, 13,500 btu or 15,000, and what generator you are using. May help you figure out if is marginal. Also test it with a volt meter while running a shop vac, microwave, or something that draws some current, but not as much as your AC. The generator may have developed a problem.

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