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Old 06-05-2012, 02:52 PM   #1
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Roof AC problem

Searched this Forum and didn't find much about this. Maybe you AC mechanics will know.

My front roof AC is giving signals that it may be low on freon, I know it's not actually freon now-a-days, but I'll call it that. When it first comes on, after being off overnight, the compressor runs for about 10 seconds and then cuts off. It stays off for 2 minutes and 10 seconds, (compressor delay protector I think) and comes back on and runs for 20 seconds and cuts off, and it stays off for the 2 minutes, 10 seconds, etc. This cycling continues and each time the compressor runs for a little longer period, finally running for up to 1 minute before cutting off, and then it does the cycle routine. When the compressor does run, it blows cold air. I'm thinking it must be low on freon and the pressure switch in the freon line low side cuts the compressor off. The pressure then builds up a bit keeping it running a little longer each time.....up to a minute. It could also be a bad freon level sensing switch. Does anyone know if these AC's have a port for adding freon? Any suggestions or advice? Rook
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Old 06-05-2012, 02:59 PM   #2
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Does sound like you are low on freon-For the ac mechanics they need make/model numbers.
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Old 06-05-2012, 03:45 PM   #3
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Hello Rook, yes is it a Coleman or a Dometic, I'm not an AC mech, but I believe those are closed systems, i.e., they don't have a way to add Refrigerant to the system.
I might be wrong on that, have been in the past
I have fixed my dometic by changing out a bad capacitor, and fixed my dash air, but havn't found any way to add refigerant to those systems.
Now I do believe that an AC mech may be able to tap into the low pressure side and add refrigerant to it, beyond my pay grade

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Old 06-05-2012, 03:59 PM   #4
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there is a fix for this, if it is low freon. It is called a piercing valve. They are available from any AC supply co.
I don't think that is your problem. Most R22 freon AC's don't have low pressure switch's. It sounds like a Electrical problem.
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Old 06-05-2012, 04:03 PM   #5
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Quote:
Originally Posted by 87Rockwood View Post
Does sound like you are low on freon-For the ac mechanics they need make/model numbers.
It's a Dometic "Brisk Air". Don't know the model or product number yet.......haven't been on top yet. Rook
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Old 06-05-2012, 04:08 PM   #6
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I have been meaning for months to post the piercing valve information, For those who have low freon in a roof AC. One piercing vale is made by Supco. The part number is BPV31. It fits 1/4, 5/16, and 3/8 tubing.
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Old 06-05-2012, 04:18 PM   #7
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Yep sounds like it is low on freon. Seems to be short cycling and thermal disc is cutting out compressor, The freon is used to cool the compressor motor with thermisters , also it would have tapped to add freon.which is no biggie. Unless you have a bad leak in your evaporator coil.
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Old 06-05-2012, 04:27 PM   #8
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I would never use a piercing valve because they will leak as time goes on due to rubber seal rottening on copper tubing, who ever does it tell them to put you a tap which is permanent and will not leak over time. Hope this helps you.
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Old 06-05-2012, 04:52 PM   #9
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It would be very unusual for a roof AC unit to lose freon. They are a hermetically sealed system such as used in a refrigerator, or a window AC unit. They are sealed 100% at the factory. Not saying that it is impossible but most unlikely. The compressor sits inside a sealed tank. This is not like a car AC system that has shaft seals or rubber hoses and couplings and such. If it did leak then there is no point in just putting in freon without fixing the leak. My guess it is some other problem and you would probably save money by having a professional look at it before breaking into that sealed system.
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Old 06-05-2012, 05:54 PM   #10
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Better than 90% of the A/C problems are NOT low on Freon, but tat is usually the first thing a novice will come up with. As noted, the units are hermetically sealed and there is no place for the refrigerant to leak out unless you have a line crack, a pin hole develop or physically damage the unit.

Start by pulling the inside cover and check the evaporator for dirt and lint. The air filters need to be cleaned about every 14 days of use. Next get a volt meter and an amp meter and check the volts and amps at the compressor.

Next, you may have a start capacitor that may be going bad. They can be checked, but it takes a special meter. Capacitors are pretty inexpensive, so you might pick one up and change it.

Low voltage (below 108 volts) and a bad start capacitor can keep you from starting.

The last thing is the unit is 14 years old by the age of your coach. It may have a compressor going bad and time to replace it.

Generally, that age unit is not worth the cost of properly recharging it. The piercing valve, more commonly called a saddle clamp or saddle valve will leak. It is not a matter of if, but when. They are a temporary fix and used to diagnose a problem. The unit needs to be completely evacuated, purged with nitrogen and Schrader valves soldered into the lines for a proper fix. Then the unit need to be evacuated and recharged with refrigerant. You will spend half the cost of a new unit unless you can do the work yourself.

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Old 06-05-2012, 07:28 PM   #11
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Rethinking the problem

Thanks for all the comments.....some good points have been stated, causing me to rethink the problem.

1) I didn't realize that the system was "hermetically sealed"......thereby making the loss of refrigerant very unlikely. There is no physical damage, either. And.... there is no "low-side" pressure switch in these units, so that's not what's cutting the compressor off after 10 seconds.
2) The compressor starts easily....but initially only runs for about 10 seconds and then "something" cuts it off! Then after 2 minutes 10 seconds (the fixed period compressor delay), it starts right up again and runs for about 20 seconds and then "something" cuts it off! And.....eventually it will run for up to a minute before "something" cuts it off. That does not sound like a starting capacitor would cause this. Could it?
3) So. what is the "something"? Question: What else besides the thermostat has the ability to cut the compressor off? Rook
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Old 06-05-2012, 07:38 PM   #12
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It would be worth checking, if you have floor ducting, a rug over a vent can cause short cycles


Quote:
Originally Posted by Rook
Thanks for all the comments.....some good points have been stated, causing me to rethink the problem.

1) I didn't realize that the system was "hermetically sealed"......thereby making the loss of refrigerant very unlikely. There is no physical damage, either. And.... there is no "low-side" pressure switch in these units, so that's not what's cutting the compressor off after 10 seconds.
2) The compressor starts easily....but initially only runs for about 10 seconds and then "something" cuts it off! Then after 2 minutes 10 seconds (the fixed period compressor delay), it starts right up again and runs for about 20 seconds and then "something" cuts it off! And.....eventually it will run for up to a minute before "something" cuts it off. That does not sound like a starting capacitor would cause this. Could it?
3) So. what is the "something"? Question: What else besides the thermostat has the ability to cut the compressor off? Rook
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Old 06-05-2012, 07:49 PM   #13
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It would be worth checking, if you have floor ducting, a rug over a vent can cause short cycles
The ducting is in the roof and also used by the rear AC......and the rear AC works just fine. Initially, the Compressor does not run long enough (10 seconds, 20 seconds, etc.) to get anything hot! Rook
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Old 06-05-2012, 08:09 PM   #14
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Rook have you check the amps and volts and compared them to the rear A/C?

ken
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