trouble shooting a 1998 U270 FT A/C

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trouble shooting a 1998 U270 FT A/C

April 20, 2017, 03:14:54 pm

I have read all the material available on the forum, so I hope that I am not missing the post that was already done. I would like some direction on which way to go on my A/C adventure. I have previously had Bern'd replace compressor and dryer, MOT evacuation of system and recharge, FT replace condenser, evacuate and charge system. FT pulled a 28 vacuum and held it for over hour. But like the annual passage of time; the a/c refuses to work again.
The compressor cycles on and off is constantly cycling.
Why can system hold a vacuum and still leak out the freon?
Where do I need to start my search. I plan on putting dye into the system only adding enough freon to get the system circulating. And looking for the leaks. When FT did the work the a/c lasted several days so is the leak large or small that I am searching for? Thank you.

Re: trouble shooting a 1998 U270 FT A/C

Reply #1 – April 20, 2017, 03:30:35 pm

A/C leaks can consume a lot of time trying to locate.You could use a dye but you are also going to have to recharge the system so it can circulate and have time to actually leak out. What you need is Dry Nitrogen. You can put a small amount of trace refrigerant in and then pressurize with the nitrogen. A sniffer or soapy bubbles can then be used. Once you locate the leak or leaks and have it/them fixed . You can pressurize with nitrogen and check again. The nitrogen can be dumped You'll be feeding the plants. Then a vacuum is pulled which should be done through a micron gage. Then held to see if you lose that deep deep vacuum. Then recharged. To start I would look at every line fitting for any sign of oil,at the compressor condenser ,etc It could be in the evaporator itself,it's a search and find it kind of thing.

Re: trouble shooting a 1998 U270 FT A/C

Reply #2 – April 20, 2017, 03:52:26 pm

After three coaches and almost 400k miles, I came to the conclusion that when something fails, don't fool around unless you have nothing better to do. I've had many "appliances" re-built, only to have them fail again. What we do now, is "buy fresh" from a pro with all the warranty. Yes, CB city, but something else to not worry about, unless you like that.

Re: trouble shooting a 1998 U270 FT A/C

Reply #3 – April 20, 2017, 05:40:19 pm

I have tried FT, MOT, Bern'd at over several coach bucks and the a/c works like it did before they started; NOT. So where do you find a specialist in Illinois that knows how to fix it? And how will I know that it is not another fishing expedition.
FT built it and they were unable to fix it. So where do I go to get someone that will fix it?

Re: trouble shooting a 1998 U270 FT A/C

Reply #4 – April 20, 2017, 06:06:41 pm

Quote from: John/Pat – April 20, 2017, 05:40:19 pm

I have tried FT, MOT, Bern'd at over several coach bucks and the a/c works like it did before they started; NOT. So where do you find a specialist in Illinois that knows how to fix it? And how will I know that it is not another fishing expedition.
FT built it and they were unable to fix it. So where do I go to get someone that will fix it?

Even when running at their best, most motorhome otr ac's do not do much more than keep your face cool.
A lot of people just run their generators and roof ac's when travelling.

Re: trouble shooting a 1998 U270 FT A/C

Reply #5 – April 20, 2017, 06:34:34 pm

I had problems like many have discussed. The last one was an electricl one which Stump held my hand and we solved it. Prior when I bought the coach dash ac wasnt working. I took it to Hudson Automotive in Fruitland Park Fl. They got it running. However my controls for defrost and dash dont work. But they wired the floor damper open so I can get heat and AC. One day I'll get into the controls which several members have done and I'll follow the steps they did. RV shops arent the best for AC issues. Search your area for an AC guy. Or listen to Stump he is pretty smart.

Re: trouble shooting a 1998 U270 FT A/C

Reply #6 – April 20, 2017, 06:51:18 pm

Go to HF and buy a set of A/C gauges not that expensive. If it only worked for 2 days after FT it is a fairly large leak. A good automotive A/C shop will have a sniffer to get close to the leak. I own one myself as I have done automotive A/C repair on all my vehicles. It can be fixed. I still have 40 deg. at the dash register 14 months since I repaired it.

Re: trouble shooting a 1998 U270 FT A/C

Reply #7 – April 20, 2017, 09:34:23 pm

John,

When you charge your system don't forget to add oil.

Actually I did not know those things were supposed to work.

Craneman is one of the few that I have heard of that has one

over 5 years old that actually works.

Good luck in your repair,

Carter-

Re: trouble shooting a 1998 U270 FT A/C

Reply #8 – April 20, 2017, 09:53:45 pm

Is there a way of telling if Bern'd replaced the oil when he changed the compressor? I am not sure if FT replaced it when they changed the condenser.
Should each shop after changing a major component have replaced oil. I will check my invoice from FT.
Is there a way of checking the oil?

Re: trouble shooting a 1998 U270 FT A/C

Reply #9 – April 20, 2017, 09:55:17 pm

Bear in mind that even if you do get it working perfectly, your max.output will only be about 17000 btu. This is about the same as a average midsize car, except that you will have another 30 ft or so of hot coach to cool.

Re: trouble shooting a 1998 U270 FT A/C

Reply #10 – April 20, 2017, 10:06:13 pm

Quote from: John/Pat – April 20, 2017, 09:53:45 pm

Is there a way of telling if Bern'd replaced the oil when he changed the compressor? I am not sure if FT replaced it when they changed the condenser.
Should each shop after changing a major component have replaced oil. I will check my invoice from FT.
Is there a way of checking the oil?

Anytime a major component is replaced, the system is usually evacuated, this will remove all refrigerant and oil.
A decent tech will replace the correct amount of oil [according to system size] when replacing the refrigerant. Once the oil and refrigerant are in in the system, there is no way to check oil level. [Stationary compressors may have a sight glass in the compressor crankcase] but auto systems do not.

Re: trouble shooting a 1998 U270 FT A/C

Reply #11 – April 20, 2017, 10:47:07 pm

I run the generator when traveling so both a/c are running, however, I would like the a/c dash to work also. I like it cold while traveling.

Re: trouble shooting a 1998 U270 FT A/C

Reply #12 – April 20, 2017, 11:11:44 pm

Evacuating the system does not remove the oil just moisture and refrigerant. You have to drain the compressor and flush the system to remove the oil. Most compressors come with the oil in them. The label lets you know whether oil has been installed. Changing the drier, and the expansion valve will still leave oil in the system. The pressures keep most of it in the compressor.
On our coach the dash air will blow cold air on me and my DW it does not cool beyond the living room. We need the front roof air added to be comfortable in the kitchen if the bedroom door is closed.

Re: trouble shooting a 1998 U270 FT A/C

Reply #13 – April 20, 2017, 11:35:17 pm

Since I had to replace my compressor among and other components I installed service valves on the Seltec compressor so that I can check the oil level without pulling out the refrigerant. Valve off the compressor, slowly remove the oil fill bolt on top to bleed off the pressure, once removed use Seltec dip stick or a wire to determine the oil level. Re install the bolt but leave it lose, open the service valve a little to allow the refrigerant to pressurize the compressor to bleed out the air, doesn't take much. I flush my line sets out and it took a 1/2 quart of oil to level the system out. By the way the evaporator in my rig is only a one ton coil, not much but nice to have here in Arizona when it is 110 degrees outside.

Re: trouble shooting a 1998 U270 FT A/C

Reply #14 – April 20, 2017, 11:40:40 pm

Quote from: craneman – April 20, 2017, 11:11:44 pm

Evacuating the system does not remove the oil just moisture and refrigerant. You have to drain the compressor and flush the system to remove the oil. Most compressors come with the oil in them. The label lets you know whether oil has been installed. Changing the drier, and the expansion valve will still leave oil in the system. The pressures keep most of it in the compressor.
On our coach the dash air will blow cold air on me and my DW it does not cool beyond the living room. We need the front roof air added to be comfortable in the kitchen if the bedroom door is closed.

Agree, should have specified the compressor and flush. Good article about adding oil if necessary.
PAG Oil For A/C Maintenance Helps To Avoid Compressor Failure

Re: trouble shooting a 1998 U270 FT A/C

Reply #15 – April 20, 2017, 11:54:32 pm

Coach dash a/c has to be very carefully designed due to the lenght and the environment that the liquid line operates. If the LL is too small and it runs through hot environments (assuming condenser coil is in the rear on non GV coaches) the heat and pressure drop can cause the liquid to boil or "flash" which will drive the expansion valve bonkers. Front mounted condenser coils receive hot gas that is condensed into liquid and only run a short distance to the evaporator coil and this should not be a problem. Rubber hoses designed for one refrigerant may not be suitable for a substitute refrigerant due molecule size and allow leakage. Evacuations from the suction side of the system remove very little oil because the oil doesn't boil off much. So each time it is recharged and a tech adds oil to be safe really kills capacity as oil does do any work in the coils and hinders heat transfer. Add to it off the long suction side hoses carrying 40 degree vapor should be insulated with proper insulation. On top of that the dirt build up on unfiltered evaporator coil and fan blades further leads to system degradation. Most can be fixed by a local tech, switch to properly sized new insulated (except copper hot gas) copper lines thru the beast and clean the dirt off of the fan blades. Clean the condenser coil and check that the high pressure switch is operating the condenser fan.

Re: trouble shooting a 1998 U270 FT A/C

Reply #16 – April 21, 2017, 12:07:40 am

Ok I'm a really slow typer on my smart phone and 4 replies came in

Re: trouble shooting a 1998 U270 FT A/C

Reply #17 – April 21, 2017, 09:34:50 am

Quote from: John/Pat – April 20, 2017, 05:40:19 pm

So where do you find a specialist in Illinois that knows how to fix it?

I would try one of these places;
Truck Refrigeration Unit Repair Directory | Illinois | Reefer Repair...

Thermo-King is a big outfit.

Re: trouble shooting a 1998 U270 FT A/C

Reply #18 – April 21, 2017, 09:59:28 am

I second the comment about using Nitrogen and leak indicator. The higher differential pressure gives you over vacuum greatly accelerates the leak indication. The smallest of leaks will show in minutes. To finally remove all the leaks from my 1996 coach, I replaced compressor, evaporator, and all the rubber refrigerant lines. I am betting you have a leak in the evaporator.

Re: trouble shooting a 1998 U270 FT A/C

Reply #19 – April 21, 2017, 10:02:54 am

Good idea but those above places specialize in refrigeration of the trailer,I would either buy a leak detector or find a good auto
ac place near you that won't mind trying to find a leak in your system.You can buy a detector for about 1 1/2 hours labor.Having
read your sequence of events it seems after it leaks out you take it to a shop and they vacuum and recharge,thats not fixing the problem.If you get a detector you can also buy a 30 lb can of R134 and put 40 psi in the system and check for leaks.

I agree you have a major leak that no leak stop will fix,if at some point it gets to a lesser leak you can use a product called
"red angel" it comes in 2 oz and is the best product for fixing ac leaks.

Re: trouble shooting a 1998 U270 FT A/C

Reply #20 – April 21, 2017, 10:24:11 am

When a compressor short cycles it generally means that it is low on coolant. True, but it could be an electrical issue or sensor. Also, when there is a leak, it usually leaves a tell-tale indication of oily stain. Except, sometimes you will have a high pressure hose that will weep like osmoses through the entire hose and it's hard to detect because it's all stained. Point being, it might not be a single point leak, like a connection point. Also, with a vacuum check you are getting a static test that might not pick up issues in the compressor that might only leak when it is running. Everything I read on the forum looks like a look of good advice from lots of experienced (hot) RV'ers. Personally I might would replace the compressor and then start looking for leaks. Good luck.

Wantabe

Re: trouble shooting a 1998 U270 FT A/C

Reply #21 – April 21, 2017, 10:32:50 am

This is what I bought, but it was less than half the price a year ago. Since you have the gauges and the vacuum pump having a bottle will let you maintain the A/C after you get it fixed. Hoses have been the leaks in my previous motorhomes. The coach I have now didn't have a leak other than the compressor seal. I changed the expansion valve and the drier as they needed to be removed to do a good flush along with the compressor to have a fresh start on all the components other than the thermostat as it would have been very difficult to reach.

https://www.samsclub.com/sams/johnsen-s-r-134a-refrigerant-cylinder-30-lbs/156595.ip?xid=plp:product:1:1

Re: trouble shooting a 1998 U270 FT A/C

Reply #22 – April 21, 2017, 11:12:04 am

Reading through all of this good stuff gets me to thinking that there are a lot of FT's out there with bad dash AC, me included. Running down the road with the little generator running and the front roof unit on seems to be the cheaper way and gets you cooler faster.
Speedbird 1.

Re: trouble shooting a 1998 U270 FT A/C

Reply #23 – April 21, 2017, 11:28:19 am

With these rolling greenhouses the dash air is a great help. Automotive refrigeration is really not that difficult to diagnose and repair if you buy the above mentioned tools, gauges, vacuum pump, leak detector (sniffer) and UV glasses for the dye. Then you can keep up with your cars, trucks or whatever else you have that uses refrigeration. I even use it to keep the house air going. There are U Tube videos out there on how to change heater and evap. cores in automobiles that let me do my 2001 Grand Cherokee air when the evap. core failed.
Also remember the roof air is 13,000 btu and the dash is more than that.

Re: trouble shooting a 1998 U270 FT A/C

Reply #24 – April 21, 2017, 11:28:28 am

I agree but I like both.

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