Roof AC Questions

[HamboneTHW]

So this is our first RV. We just got back from a little over a week in TX in pretty brutal summer heat. I have a few questions regarding roof top ACs:

1. Is it normal for rooftop ACs to run pretty much constantly through the day during the summer?

2. Both ACs at times make squeaking noises. These noises eventually dissipated, but would come and go. Is this normal? Is there something that I should look at?

3. I cleaned the coils with a brush to remove debris, being careful not to bend fins. Is there another way I should be cleaning the coils?

4. Is there an easy way to overhaul these ACs?

5. When do you know it's time to replace rooftop ACs? If I were to go with newer units, will existing wiring work for the new thermostat and new units? Or will they require new wiring runs for controls and power?

6. I stay plugged in at the house. I'm worried about the massive rise in electricity consumption. What is the most economical set point to maintain suitable humidity levels in the coach?

As always, thank you all in advance.

[RVPioneer]

What temp are you trying to maintain in 90°+ temps with high humidity? If you're trying to get the coach to 72° the AC's will probably run constantly. If your willing to settle for 78-80° they may shut off periodically. It will be especially difficult if the coach is sitting in full sun or if the windshield is exposed to direct sun. We use the silver reflective sun shields when necessary.


The front AC controls the rear. We replaced our rear unit and a new circuit board needed to be installed in the front unit to control the rear. The rear unit works like gangbusters. Practically froze us out of the bedroom in 90+ temps in Kentucky a few weeks ago. I would have liked to have had the front replaced but nothing was found to be defective that would have warranted replacement under our ESP.


Each unit appears to draw about 11 amps so a bit of math will give you an estimate on how that will effect your electric bill.


Like most things these days if something needs to be repaired it generally just gets replaced. And you have to wonder if it is worth the time and effort to try to keep a 14 year old AC running.


As far as humidity levels go it will be a challenge in the summer in Tennessee. You could try a couple of the 30w electric dehumidifiers, some of the moisture absorbing crystals and a fan for circulation. Perhaps with just one AC set in the low 80's it will keep the moisture under control without skyrocketing your electric bills. Is the coach parked inside? Under cover? Or in a shady area?

[BFlinn181]

Originally Posted by HamboneTHW

So this is our first RV. We just got back from a little over a week in TX in pretty brutal summer heat. I have a few questions regarding roof top ACs:

1. Is it normal for rooftop ACs to run pretty much constantly through the day during the summer?

The fans will run continuously to move air around, the compressors as needed. Do you have all windows covered? The front pointing away from South, these steps help insulate from the heat.

2. Both ACs at times make squeaking noises. These noises eventually dissipated, but would come and go. Is this normal? Is there something that I should look at?

Some makes, models of A/C units have squirrel cage fans that can break or become out of balance. Doesn't sound like that's your problem, especially since you said the noise has gone away. The noise could also be from trim or covers vibrating.

3. I cleaned the coils with a brush to remove debris, being careful not to bend fins. Is there another way I should be cleaning the coils?

You can buy cans of spray coil cleaner that help remove dirt and clean the condenser and evaporator coils. Awesome or Simple green might not be good for the aluminum fins, check online to be sure.

4. Is there an easy way to overhaul these ACs?

Beyond keeping them clean, No. The compressor is a sealed unit, there are no ports to add refrigerant. (Piercing ports can be added to add refrigerant, but that doesn't solve the leaking that caused the loss of refrigerant.) Fan motor can be replaced, start/run capacitors can be replaced, some folks 'upgrade' to 'hard start capacitors.

5. When do you know it's time to replace rooftop ACs? If I were to go with newer units, will existing wiring work for the new thermostat and new units? Or will they require new wiring runs for controls and power?

Wiring should be compatible, you have to pay attention to thermostat compatibility, but the manufacturer or a good RV A/C retailer should know if your thermostat will work with new units.

6. I stay plugged in at the house. I'm worried about the massive rise in electricity consumption. What is the most economical set point to maintain suitable humidity levels in the coach?

If you're not using the RV, why are you keeping it on HVAC? Cracking a vent and a window will allow cross ventilation and prevent build-up of condensation. You won't prolong RV life by leaving HVAC on, you will wear out the A/C and furnace, and as you noticed, you will have a large utility bill. Worst sources of humidity inside the RV are people and pets, if you're not staying in it, outside air won't hurt it.

As always, thank you all in advance.

I hope I answered your questions.

[DrDaveMA]

One of your best investments will be awnings on the windows. We also have an exterior shade for the windshield. Using both and starting the A/C early in the morning will make it cooler, we normally see a 10 degree drop, so that added to about 20 degree cooling, you will be able to handle the higher temps.

[HamboneTHW]

Originally Posted by BFlinn181

I hope I answered your questions.

Thank you for the response. When you leave a roof vent cracked, do you leave the fan running? I leave everything plugged in so the residentail fridge runs. Would the heat build up affect that?

I'm really just trying to figure out if the juice is worth the squeeze with replacement. Looks to be about $2000-$2500 to replace both units. The coach stayed reasonably cool (had the front unit set to 76 and the rear to 73). They were running pretty much all day, but outside temps were in the high 90's. It sounds like that is normal, whether I am running the older units or newer ones.

[HamboneTHW]

Originally Posted by DrDaveMA

One of your best investments will be awnings on the windows. We also have an exterior shade for the windshield. Using both and starting the A/C early in the morning will make it cooler, we normally see a 10 degree drop, so that added to about 20 degree cooling, you will be able to handle the higher temps.

Dave,

Thanks for the response. I have awnings over the exterior windows and did utilize them. I left the thermostats set at the same temperatures the whole time.

Can you send a link to the exterior shade for your windshield? I felt a lot of heat coming in through the windshield, even with the shade down.

[Dreamacre]

When we are out and it is hot outside, we place a "Cyclone" ($25 at Walmart) fan between the front seats at an angle to the ceiling. This keeps the air moving and allows the A/C compressors to shut off every now and then. It is quite comfortable at 78 degrees.

[HamboneTHW]

Originally Posted by RVPioneer

What temp are you trying to maintain in 90°+ temps with high humidity? If you're trying to get the coach to 72° the AC's will probably run constantly. If your willing to settle for 78-80° they may shut off periodically. It will be especially difficult if the coach is sitting in full sun or if the windshield is exposed to direct sun. We use the silver reflective sun shields when necessary.


The front AC controls the rear. We replaced our rear unit and a new circuit board needed to be installed in the front unit to control the rear. The rear unit works like gangbusters. Practically froze us out of the bedroom in 90+ temps in Kentucky a few weeks ago. I would have liked to have had the front replaced but nothing was found to be defective that would have warranted replacement under our ESP.

Each unit appears to draw about 11 amps so a bit of math will give you an estimate on how that will effect your electric bill.


Like most things these days if something needs to be repaired it generally just gets replaced. And you have to wonder if it is worth the time and effort to try to keep a 14 year old AC running.


As far as humidity levels go it will be a challenge in the summer in Tennessee. You could try a couple of the 30w electric dehumidifiers, some of the moisture absorbing crystals and a fan for circulation. Perhaps with just one AC set in the low 80's it will keep the moisture under control without skyrocketing your electric bills. Is the coach parked inside? Under cover? Or in a shady area?

Pioneer,

It is parked in a shadier area. It's in the driveway, but the side of the house provides some decent shade for more than half of the day.

I see a response lower mentioning cracking a window and a roof vent. I think maybe that with some dehumidifying crystal packs may work. Interested to hear what others do when they aren't using the coach to maintain humidity levels.

[HamboneTHW]

Originally Posted by Dreamacre

When we are out and it is hot outside, we place a "Cyclone" ($25 at Walmart) fan between the front seats at an angle to the ceiling. This keeps the air moving and allows the A/C compressors to shut off every now and then. It is quite comfortable at 78 degrees.

Dreamacre,

Thanks for the response. I will give that a whirl on our next trip. That's certainly a cheap option to try.

[DrDaveMA]

Originally Posted by HamboneTHW

Dave,

Thanks for the response. I have awnings over the exterior windows and did utilize them. I left the thermostats set at the same temperatures the whole time.

Can you send a link to the exterior shade for your windshield? I felt a lot of heat coming in through the windshield, even with the shade down.

Tommy, with the interior shades the windshield glass still heats up transferring that heat to the interior. To stop that you must place a shade on the outside, there are 2 types that I am aware of, those that physically clip on and those that are held in place magnetically. We had ours made while we were in Las Vegas, in I think it was 2006, by a company called RV Sun Shades. He came to the coach and custom made the shades out of a poly type screen that you can see through and they clip on. That also means people outside can kind of see in at night if the lights are on. I have heard that under some circumstances the magnetic type can be blown off, but I can not verify that, I do know I have NEVER have had ours come loose! They are still in good shape and we are very happy with them.

[BFlinn181]

Originally Posted by HamboneTHW

Thank you for the response. When you leave a roof vent cracked, do you leave the fan running? I leave everything plugged in so the residentail fridge runs. Would the heat build up affect that?

I'm really just trying to figure out if the juice is worth the squeeze with replacement. Looks to be about $2000-$2500 to replace both units. The coach stayed reasonably cool (had the front unit set to 76 and the rear to 73). They were running pretty much all day, but outside temps were in the high 90's. It sounds like that is normal, whether I am running the older units or newer ones.

With the roof vent open just a bit, I also open a window to allow air in as hot air goes out the roof vent. No fan, just natural convection.

[wolfe10]

Originally Posted by BFlinn181

With the roof vent open just a bit, I also open a window to allow air in as hot air goes out the roof vent. No fan, just natural convection.

With the high humidity in Texas right now (assume you are in the "damp" part with dew points in the high 70's) I would NOT leave a window open and/or use a vent.


Takes way too many BTU's to squeeze the water out of the air to introduce more hot humid air.

[BFlinn181]

Originally Posted by wolfe10

With the high humidity in Texas right now (assume you are in the "damp" part with dew points in the high 70's) I would NOT leave a window open and/or use a vent.


Takes way too many BTU's to squeeze the water out of the air to introduce more hot humid air.

Most vehicles left unoccupied shouldn't be damaged by atmospheric humidity. If you have power, you could close up the RV and use a dehumidifier, but I just park it without power and leave cabinets, refrigerator, and closets open a bit so air can circulate.

Keeping the RV closed up is when heat on one side and shade on the other could allow moisture to collect and start mold or mildew. I've had cabin cruisers and RVs for over 40 years and never left one stored all buttoned up. Never had a mold or mildew problem either.

[wolfe10]

Bob,


We may be talking about different circumstances.


I was talking about when in the coach and using the roof A/C's. I would not open a window or turn on a vent fan except when first getting to the coach to rid it of "hotter than ambient" temperatures. Once the A/C's drop temperatures below ambient, shut everything up.



For storage, I am a STRONG believer in a small house-type dehumidifier draining into the gray tank. Do that on all my RV's and also on the sail boat. Set humidity at 50% and never have any mold or mildew. Again we are talking about what to do in humid conditions-- our dew point right now is 78 degrees!