Main A/C problem

[Ice 1]

I have a 2013 toy hauler with a ducted A/C in main and a stand alone A/C in master. We've had the RV for almost a year with few problems. The main A/C has stopped cooling. I inspected the evap coil about a month ago and it was frozen, sometimes an indication of low refrigerant. This is an airxcel unit, Model 48254C969, which has no access ports to check pressures or add refrigerant. The compressor is to hot to touch. Unless someone has an idea on repair my question is what to purchase to replace. This is on a duct so it doesn't seem like I would need to purchase a ceiling assembly? Could I just replace the upper unit?

Thanks

[chuckster57]

Welcome to the forum!

RV A/C units aren't built with service ports and are considered "throw away" when this sort of thing happens. Low charge is usually verified by measuring amp draw, but since your out of warranty and replacement would be the quickest, yes you can get just the portion that sits on the roof.

[Steve S]

Welcome to the forum!

RV A/C units aren't built with service ports and are considered "throw away" when this sort of thing happens. Low charge is usually verified by measuring amp draw, but since your out of warranty and replacement would be the quickest, yes you can get just the portion that sits on the roof.

Hi chuckster57 I'm curious about the amp draw. What's the typical amp draw of a good AC compared to the amp draw of a dieing AC? I'm pretty sure that this is the first time that I've read about this. Thanks:)

[chuckster57]

I don't remember of the top of my head. When we diagnose a bad compressor/low charge, we download and print out a work sheet. It has space for ambient air temp, temp at ceiling vent, amps being drawn.

Haven't done one for a while, so figures aren't fresh in my mind. Sorry :o

[Steve S]

I don't remember of the top of my head. When we diagnose a bad compressor/low charge, we download and print out a work sheet. It has space for ambient air temp, temp at ceiling vent, amps being drawn.

Haven't done one for a while, so figures aren't fresh in my mind. Sorry :o

Yeah I guess that as you've stated above that they're more of a throw away item that you don't really mess with them as it's not worth the shop time to the customer as a refit is pretty simple and doesn't take all day to do.

[chuckster57]

With a forklift to hoist the unit on the roof, replacement is about 30 minutes total time if I go slow.

[JRTJH]

Steve,

The amp draw for the compressor (if the Freon capacity is full) is the rated load (found on the data plate) at 95F. As the temp goes up, the amperage goes up and as the temp goes down the amperage goes down.

You can download the Airxcel troubleshooting guide here: http://www.airxcel.com/docs/default-source/coleman-mach/mach-8-ac/evaluating_ac_performance.pdf?sfvrsn=19

The compressor amp table is on page 2, but it's only a 2 page document, full of some "good info" for understanding how to determine the Freon charge using a clamp on ammeter.

[xrated]

Before you write it off, make sure that the evaporator fan is turning and that it is turning the proper speed. Lack of air flow across the evaporator coil will cause an A/C unit to freeze up also. If the evap fan seems to be OK, close every thing back up and make sure that all of your vent in the ducted system are open also. A lack of air flow because vents are closed up and or blocked and insufficient airflow will cause freezing up of the evaporator. I'd hate to see you replace the entire unit and it's something simple like an air flow issue.

[JRTJH]

To add to xrated's comments, there is a "freeze plug" mounted in the upper portion of the evaporator. It's purpose is to detect and prevent ice formation in the fins. Looking back at your first post on the subject, you mention that your A/C "froze up". You might have, in your travels, vibrated the "freeze plug" out of position. Look for two wires in the return air box that go to a "little black thing" that is supposed to be inserted between the evaporator fins. If it's in position and working, you shouldn't ever have ice formation on the evaporator. If it's out of position or inoperative, then ????

[Steve S]

Steve,

The amp draw for the compressor (if the Freon capacity is full) is the rated load (found on the data plate) at 95F. As the temp goes up, the amperage goes up and as the temp goes down the amperage goes down.

You can download the Airxcel troubleshooting guide here: http://www.airxcel.com/docs/default-source/coleman-mach/mach-8-ac/evaluating_ac_performance.pdf?sfvrsn=19

The compressor amp table is on page 2, but it's only a 2 page document, full of some "good info" for understanding how to determine the Freon charge using a clamp on ammeter.

Thanks John it's nice to learn something new everyday. :)

[chuckster57]

Thank you John for the link. I usually get the R/O and a printed worksheet, bring the unit up and start filling in blanks. In this wonderful digital era I even have to have pics of the amp gauge readings.

[Ice 1]

Thank you John for the link. I usually get the R/O and a printed worksheet, bring the unit up and start filling in blanks. In this wonderful digital era I even have to have pics of the amp gauge readings.


Thanks for all help. I should have been more clear as a while ago the evaporator coil was completely froze but now only has small amount of ice on entry to evap. I didn't measure amp draw but feel it will be high given the hot compressor. I will change the upper unit. Thanks y'all

[JRTJH]

Thanks for all help. I should have been more clear as a while ago the evaporator coil was completely froze but now only has small amount of ice on entry to evap. I didn't measure amp draw but feel it will be high given the hot compressor. I will change the upper unit. Thanks y'all

Before you pull the old unit, check the "freeze detector plug". While it's entirely possible for a 4 year old unit to fail (my upper unit leaked all the Freon in 6 months and failed) with the evaporator frozen, that "little black thing" stuck between the fins on the evaporator will produce exactly the symptoms you've got.

As for "physical function" it's a thermal relay (thermocouple) that opens at 41F and closes at 51F. I can't remember the exact numbers, but that's close. Essentially what it does is control the flow of Freon through the system to prevent the evaporator fins from getting too cold, thereby keeping them from freezing and allow the condensate (water) on the fins to remain flowing, drying the air without blocking them with ice.

[Ice 1]

Before you pull the old unit, check the "freeze detector plug". While it's entirely possible for a 4 year old unit to fail (my upper unit leaked all the Freon in 6 months and failed) with the evaporator frozen, that "little black thing" stuck between the fins on the evaporator will produce exactly the symptoms you've got.

I have seen this "freeze detector plug" and it is inserted in the fins of the coil but I'm not sure if it is working correctly. I assume it is a thermister or something similar. Is there a way to check this? Resistance?

Thanks

[xrated]

If it's a thermister, attach a set of leads on it from a multimeter, set on ohms, and note the resistance reading. Now place the thermister in the freezer section of your refrigerator and leave it there for 10 minutes or so, then pull it out and quickly take another ohm reading. There should be some amount of resistance difference between the two locations. I don't know exactly what, but you can probably find that info online somewhere.

OBVIOUSLY, THE THERMISTER NEEDS TO BE REMOVED FROM THE A/C UNIT AND. NO POWER ON IT.

If it's a simple clixon type switch, it will be open in one location and closed in the other.

[Ice 1]

So if it is open wouldn't it keep the compressor from running? This compressor is always running and is very hot. Or maybe it controls an expansion valve?

[xrated]

I don't know much about RV air conditioning units, but I would think that a thermister would need to be used with a TEV... vs. A capillary type system. Again, I'm not very knowledgeable on RV systems and what components they use vs. A home A/C

[Ice 1]

Before you pull the old unit, check the "freeze detector plug". While it's entirely possible for a 4 year old unit to fail (my upper unit leaked all the Freon in 6 months and failed) with the evaporator frozen, that "little black thing" stuck between the fins on the evaporator will produce exactly the symptoms you've got.

As for "physical function" it's a thermal relay (thermocouple) that opens at 41F and closes at 51F. I can't remember the exact numbers, but that's close. Essentially what it does is control the flow of Freon through the system to prevent the evaporator fins from getting too cold, thereby keeping them from freezing and allow the condensate (water) on the fins to remain flowing, drying the air without blocking them with ice.

Ok. Then with it being an open/close type thermal, should be easy to trouble shoot. I assume the close condition would open the TXV?

[JRTJH]

Yup, I think you're right. Keep in mind that I'm going on what I've read and my VERY LIMITED personal experience in troubleshooting my "busted A/C" 2 years ago. I tested mine by unplugging it, put it in the freezer with the plug hanging out the door. With an ohmmeter on the plug, I could tell when it cooled down enough to open the contacts and then when I took it out of the freezer and it warmed up, the contacts would close. I read "somewhere in a troubleshooting guide" that the temperature was "open at 51F" and "close at 41F". Don't quote me on those temps though, it's been at least 2 years since I was fighting that battle.