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Old 04-23-2022, 04:07 PM   #1
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A/C High Cool Only

Greetings, I have 2 Dometic Mach (RVP) AC units on my 1998 Fleetwood pace arrow 36B. My AC system uses a dual intellic old school thermostat. It has low and high fan and low and high cool. At each setting the roof units just hum, no fan spin. After a few tries I can usually get the fwd AC to run on high cool and I have to try several times to get the rear AC to run but only on high cool will the motor spin the fan.

I have changed all capacitors, tried to manually spin the fan with no luck. They work when they want to and that’s only on the high cool setting. Help.
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Old 04-23-2022, 06:33 PM   #2
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Quote:
Originally Posted by Qstaar17 View Post
Greetings, I have 2 Dometic Mach (RVP) AC units on my 1998 Fleetwood pace arrow 36B. My AC system uses a dual intellic old school thermostat. It has low and high fan and low and high cool. At each setting the roof units just hum, no fan spin. After a few tries I can usually get the fwd AC to run on high cool and I have to try several times to get the rear AC to run but only on high cool will the motor spin the fan.

I have changed all capacitors, tried to manually spin the fan with no luck. They work when they want to and thatís only on the high cool setting. Help.
Donít confuse the thermostats with the problem your having.

Did you lubricate the motors when you replaced the caps? Most do not have lube ports, but they can be disassembled and lubricated.
These motors donít have a lot of starting torque, and a 24 year old AC unit may very well have dry bearings. And the starting torque is marginally stronger on high speed rather than low, so explains why they tend to start when on high. But the hum is an indication that either the run cap is bad, the bearings are dry, or the units are running on less than 108vac (120vac +/-10% allowed).

You need to check voltage at the unit when the unit is trying to start. You also need to inspect all the electrical connections between your shore power connection point, through the breaker box, and at the unit for loose connections and signs of overheated wiring.
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Old 04-24-2022, 09:56 AM   #3
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Donít confuse the thermostats with the problem your having.

Did you lubricate the motors when you replaced the caps? Most do not have lube ports, but they can be disassembled and lubricated.
These motors donít have a lot of starting torque, and a 24 year old AC unit may very well have dry bearings. And the starting torque is marginally stronger on high speed rather than low, so explains why they tend to start when on high. But the hum is an indication that either the run cap is bad, the bearings are dry, or the units are running on less than 108vac (120vac +/-10% allowed).

You need to check voltage at the unit when the unit is trying to start. You also need to inspect all the electrical connections between your shore power connection point, through the breaker box, and at the unit for loose connections and signs of overheated wiring.
ThankYou for the excellent advice. No place to lube the motors and they are pretty rusty so I ordered a motor to see if this solves the problem. I made sure the connections at the Roof unit control board and capacitors were solid but I need to figure out how to read voltage at the unit with the power applied and check that’s it’s getting enough power like you said. I tend to think it’s a motor bearing issue or the motor is no longer 2 speed. Once it does get started, it does keep running on high. I think you’re right about it not being a thermostat issue. I can’t find my ECC to test the AC units anyway. Thanks again for providing direction.
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Old 04-24-2022, 10:07 AM   #4
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ThankYou for the excellent advice. No place to lube the motors and they are pretty rusty so I ordered a motor to see if this solves the problem. I made sure the connections at the Roof unit control board and capacitors were solid but I need to figure out how to read voltage at the unit with the power applied and check that’s it’s getting enough power like you said. I tend to think it’s a motor bearing issue or the motor is no longer 2 speed. Once it does get started, it does keep running on high. I think you’re right about it not being a thermostat issue. I can’t find my ECC to test the AC units anyway. Thanks again for providing direction.
Also the issue is the same on shore power and when running the generator.
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Old 04-24-2022, 10:34 AM   #5
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I trust you ordered the motor run caps, or at least checked to make sure the new ones you just installed are the same as the new motor needs.

It’s easy to lube a “sealed for life” motor, and no harder than replacing the motor - either way, you have to take the motor out of the AC unit.

Then there are 2 ways to lube the motor -

1 - Clean any rust and dirt from around the bearing hubs of the motor.
Secure and power the motor up, giving the shaft a spin if it won’t start on its own (it probably will).
Allow the motor to run for 5 minutes or so.
Disconnect power and stand the motor on one end.
Using some 10 weight non-detergent motor oil, apply the oil to the crevice between the motor shaft and bearing cap. The heated bearing will begin to draw the oil into the bearing and lubrication reservoir.
Once it doesn’t appear to be sucking more oil in, wipe off any excess, resecure and repower the motor to heat the bearing on the other end.
Lube that bearing as described above.

The method above isn’t as good as below -

2. As above, clean the shafts of the motor to remove all dirt and rust. A very fine sanding might be required using 400 grit or higher sandpaper.
Remove the nuts holding the thru bolts of the motor together.
Carefully tap on either end of the motor shaft (aka “rotor”) and one or the other end/bearing cap will pop out of the motor shell (also called a “stator”).
Carefully slide the loosened bearing cap off the shaft, being careful to retain any thrust washers with the shaft. A lite coating of oil on the shaft will aid in removing/sliding the bearing cap off.
Do the same for the other bearing cap.
Lay both bearing caps on your work surface, inside side up.
Look inside the bearing area, you should see some wicking material around the outside of the bearing.
Saturate that wicking with some 10 weight non-detergent oil. Give it some time. Keep a pool of oil on the wick until it appears not to be taking any more.
Clean up any excess oil, reassemble the end caps back onto the rotor making sure that any thrust washers and spacers have been reinstalled in exactly the same order and number as the motor was originally assembled.
Align the end cap holes with the thru holes in the stator and reinstall the thru studs and nuts.
Before torquing down the thru bolts and nuts but after the end caps are pretty much seated in the stator case, give both end caps a light love tap with the end of your nut driver or hammer. Check that the rotor shaft turns freely. If it doesn’t, make sure the bearing end caps are seated into the stator case.
Once the rotor turns freely, torque down the thru bolt nuts. Check the rotor rotation one more time to make sure it freely turns/rotates.

Reinstall the motor back into the AC unit.
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Old 04-25-2022, 03:36 AM   #6
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Quote:
Originally Posted by MrMark52 View Post
I trust you ordered the motor run caps, or at least checked to make sure the new ones you just installed are the same as the new motor needs.

It’s easy to lube a “sealed for life” motor, and no harder than replacing the motor - either way, you have to take the motor out of the AC unit.

Then there are 2 ways to lube the motor -

1 - Clean any rust and dirt from around the bearing hubs of the motor.
Secure and power the motor up, giving the shaft a spin if it won’t start on its own (it probably will).
Allow the motor to run for 5 minutes or so.
Disconnect power and stand the motor on one end.
Using some 10 weight non-detergent motor oil, apply the oil to the crevice between the motor shaft and bearing cap. The heated bearing will begin to draw the oil into the bearing and lubrication reservoir.
Once it doesn’t appear to be sucking more oil in, wipe off any excess, resecure and repower the motor to heat the bearing on the other end.
Lube that bearing as described above.

The method above isn’t as good as below -

2. As above, clean the shafts of the motor to remove all dirt and rust. A very fine sanding might be required using 400 grit or higher sandpaper.
Remove the nuts holding the thru bolts of the motor together.
Carefully tap on either end of the motor shaft (aka “rotor”) and one or the other end/bearing cap will pop out of the motor shell (also called a “stator”).
Carefully slide the loosened bearing cap off the shaft, being careful to retain any thrust washers with the shaft. A lite coating of oil on the shaft will aid in removing/sliding the bearing cap off.
Do the same for the other bearing cap.
Lay both bearing caps on your work surface, inside side up.
Look inside the bearing area, you should see some wicking material around the outside of the bearing.
Saturate that wicking with some 10 weight non-detergent oil. Give it some time. Keep a pool of oil on the wick until it appears not to be taking any more.
Clean up any excess oil, reassemble the end caps back onto the rotor making sure that any thrust washers and spacers have been reinstalled in exactly the same order and number as the motor was originally assembled.
Align the end cap holes with the thru holes in the stator and reinstall the thru studs and nuts.
Before torquing down the thru bolts and nuts but after the end caps are pretty much seated in the stator case, give both end caps a light love tap with the end of your nut driver or hammer. Check that the rotor shaft turns freely. If it doesn’t, make sure the bearing end caps are seated into the stator case.
Once the rotor turns freely, torque down the thru bolt nuts. Check the rotor rotation one more time to make sure it freely turns/rotates.

Reinstall the motor back into the AC unit.
New motor has same capacitor requirements. Thanks for providing the motor lube instructions. I may perform on the forward unit.
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Old 04-25-2022, 06:14 AM   #7
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I have been running the front AC on high cool now it shuts off sometimes while running. When I say shut off I mean the fan and the compressor. I’m able to get it going again and it runs for serval hours, like all night before it shuts off again. Sometimes it starts running again before I can start messing with the thermostat.
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Old 04-25-2022, 09:06 AM   #8
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Quote:
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I have been running the front AC on high cool now it shuts off sometimes while running. When I say shut off I mean the fan and the compressor. Iím able to get it going again and it runs for serval hours, like all night before it shuts off again. Sometimes it starts running again before I can start messing with the thermostat.
If both are shutting off then it could be the stat, or it could be a wiring issue (which is not uncommon in these units).

Simple - just reduce the stat temperature setting a little more and see if the unit comes back on.

The wiring issue could be in the breaker panel (have you checked all the breaker screwed connection points lately?) or at the unit (disconnect power to coach or open AC breaker, go on roof and access inside the electrical box and make sure all 120vac wires are good - none overheated or burned).

One thing you could do to help determine if itís the stat or wiring is to put the fan/auto switch on the stat in the fan position. The fan should now run continuous and the compressor should cycle on temperature fluctuation.

There are proís/conís to leaving the fan running all the time - 1) it keeps the air from stratifying with hot/cold spots inside the coach but 2) it allows accumulated/residual moisture on the evaporator to be rejected back into the coach when the compressor cycles off.
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Old 04-26-2022, 11:25 AM   #9
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Originally Posted by MrMark52 View Post
If both are shutting off then it could be the stat, or it could be a wiring issue (which is not uncommon in these units).

Simple - just reduce the stat temperature setting a little more and see if the unit comes back on.

The wiring issue could be in the breaker panel (have you checked all the breaker screwed connection points lately?) or at the unit (disconnect power to coach or open AC breaker, go on roof and access inside the electrical box and make sure all 120vac wires are good - none overheated or burned).

One thing you could do to help determine if itís the stat or wiring is to put the fan/auto switch on the stat in the fan position. The fan should now run continuous and the compressor should cycle on temperature fluctuation.

There are proís/conís to leaving the fan running all the time - 1) it keeps the air from stratifying with hot/cold spots inside the coach but 2) it allows accumulated/residual moisture on the evaporator to be rejected back into the coach when the compressor cycles off.
You really know you stuff. The fan has been running continuously and I had a small puddle of water drop inside the coach. The fan will not function in Fan mode. I found out the Climate Control Manager (ECC) is not fully functional. I pick up a new one today. I’m hoping this will fix the problem.
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Old 05-03-2022, 03:40 PM   #10
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A/C High Cool Only

In 2017 I had the same thing happen to my 2004 Pace Arrow 36b. Took it into an RV shop to have a service done before I headed out home to Alaska for the summer. The mechanic turned the AC on and heard that scraping noise you hear. He turned the AC off and went up to to check it out. But the time he got up there, the AC was on fire. He put it out and then checked the rear AC. Found it was also failing. Replaced both since those things are considered to be plug and play nowadays. He replaced them with two Colemans. I live full-time in a hot climate, so the AC has a heavier demand on it than the occasional RVer will have. My Repaiman that I have used for several years and implicity trust, told me they are only expected to last 5-8 years with the kind of load I'm putting on them. I had my regular RV repairman check the output on them and the rear one is barely putting out any cold air. He is replacing it with a Dometic that has a better track record for warranty work than the Coleman. With yours being a RV that is even older than mine, it might be cheaper and safer for you to replace the whole unit than piecemeal parts replace.
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Old 05-03-2022, 09:31 PM   #11
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All Fixed

Replaced both fan motors. Working like a champ. Old motors were pretty rusty.
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Old 05-03-2022, 09:34 PM   #12
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Good to hear.
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