Air conditioning

[Rotorhead]

Hello All,

we went out on a trip to the beach a few days ago. We got all set up and turned the air on. One of us turned it to 68. It was probably about 90 outside with a heat index of around 98. The air kinda worked for a while. The thermostat was acting weird to. It’s a touch screen one and the numbers were intermittent and then worked. Anyway it was not cooling down and the it quit. We packed it up the following morning and went home. On the way out an rv repair guy was there and I asked him about it. He said we froze the system by going to 68. He said never go below 72.

what do you all think?

Chuck

[Ed ke6bnl]

Sure if you leave it too low that can happen BUT if that was the case whe  you get home it would have defrosted and be working at home. Check that the fan is working, filter is clean. Doughy it was because it was set too low. 

[agesilaus]

You can unfreez it in 20 mins or so by setting the fan at high and leaving it on. When the air is blowing out the vents for 10 minutes or so it is unfrozen and you can restart the a/c.The advice I got was to leave the fan on high at all times and set the thermostat low. High humidity makes this worse.

Sometimes the freeze sensor goes bad too. That is an easy fix, unplug the old one, plug in a new one. I bought one for my unit, $18 off Amazon. Look on YouTube, lots of DIY fix it videos up there.

 

Have no ideas about the thermostat.

Edited September 3, 2021 by agesilaus

[Rotorhead]

It was all clear and blowing good. Condensation running off the roof. It seems to be working now. My wife thinks it’s not as cold as it was last month…. But it’s working. It was just weird the way it was acting.

[Rotorhead]

Freeze sensor? Guess it’s time to do some learning on the ac system. Haha

[Rotorhead]

I have a picture of the make and model and all that so I can search parts and repair info.

[Kirk W]

There are several things which can cause an air conditioner to freeze up, but setting the temperature to 68 shouldn't be one of them. If humidity is high it is far more likely to happen and several things can play a part. You mention that condensation was draining from the roof, but it is possible that the drainage was not enough to get all of the condensation away from the cooling coils. Freezing up takes place when condensation stays on the coils long enough to see temperatures below 32° for an extended period. Too little air movement through the coils can cause this also because the slower air movement allows the moisture to stay longer and the air temperature to fall lower. To check the air conditioner for proper cooling you need to check the temperature of air entering from the RV and also of the air leaving the air conditioner and that difference should be between 18° and 24° decrease. If the differential becomes too high it will cause ice to form on the cooling coils and if that continues for very long it will trigger the freeze sensor and turn the compressor off. If that happens, turning the air conditioner to blower only, moving air through with the compressor not running should melt the ice and once the ice sensor is clear the compressor should work again, if that was the cause.

All RV air conditioners that I am familiar with the only change from a setting of high cool to the low cool setting is the speed of the blower so less air passes through the coils. In my experience that can cause a freeze up if humidity is high. 

[Rotorhead]

Thanks Kirk. Next time I think I’ll climb up and look at the unit. We were at the beach and it was high humidity. 
I guess we could have shut it down and went to the beach and had fun for a few hours and then came back and tried it. 
At least they gave us a rain check. 
Chuck

[TXiceman]

The most common cause of the A/C freezing is low or restricted air flow, especially in high humidity area.  One point to note is setting the thermostat lower than the required temperature will not make the unit cool better or quicker.

In high humidity area, run the fans on high cool.  As noted if you do get a freeze up, set the unit to high fan only, not cool.  This will defrost the evaporator.

You did not tell use the make or model of the unit or the type RV you are in, ducted or direct blow air.

Some basic trouble shooting you can easily perform is as follows.

-Clean the air filter,

-Make sure the evaporator coil is clean,

-Make sure the freezestat is embedded in the evaporator.  These can vibrate loose.

-Check the air temperature across the unit with fan running on high cool.  Read the air temperature into the filter closest to the unit and then the outlet air temperature closest to the unit.  DO NOT use an infrared (laser) sensor as it will not read air temperature.  Ir reads the heat emitted form a solid surface.  Use a thermometer or a thermocouple.

-Make sure the inlet side is properly sealed from the outlet side in the plenum area and all leaks sealed at electrical connection into the roof.

Good luck.

Ken

 

 

[RV_]

Make sure bother condenser and evaporator coils are clean. Low refrigerant is a major cause of freeze up in A/C units of all types. Also pull the plenum, the inside cover filter until you get to the divider between the incoming cold air and the return warm air. if the cold air is not sealed from the other side it goes in the warm air intake and can cause a freeze up. A small leak across can cause the high humidity freeze up and operate fine in low humidity. Make sure it is sealed as well as the top side coils clean. Also check for the air seal on the sheet metal around the  under the ABS A/C shroud on top. If it has been serviced and the sheet-metal screws are missing or there are a lot of screw holes unfilled seal them with aluminum tape. 

 

Edited September 3, 2021 by RV_

[Rotorhead]

Thx TXiceman and RV.

I have a dometic 15,000 BTU ducted, with the vent to open to direct flow.

Chuck

[TXiceman]

RV_, I have to disagree.  9 times out of 10, the cause of RV A/C freezing is low or restricted air flow.  Since these are sealed systems, you will seldom get a refrigerant leak unless you got one of the problematic Dometic units from a few years ago.  With the top off, look for an oily spots on the coils or piping.

Ken

[bigjim]

I believe  I remember restricted air flow due to clogged coils mimics low refrigerant as it affects the pressure of the refrigerant in the condensor and or the evaporator. The same for lack of a proper fan flow through the condenser coil.

[sandsys]

We have only had house units fail but both of them were caused by pinholes letting the Freon leak out.

Linda

[Kirk W]

7 hours ago, sandsys said:

We have only had house units fail

A freeze up as being discussed isn't really a failure, but an operational condition with a preventive shut-down designed into the unit. 

[TXiceman]

10 hours ago, bigjim said:

I believe  I remember restricted air flow due to clogged coils mimics low refrigerant as it affects the pressure of the refrigerant in the condenser and or the evaporator. The same for lack of a proper fan flow through the condenser coil.

The low air flow through the evaporator will result in less heat load  for the coil and then less refrigerant to vaporize.  The compressor is a positive displacement device and will continue to pump the same CFM or displacement of gas.  Pulling the same volume of gas will reduce the temperature of the refrigerant as the pressure drops.  Lower pressure for the refrigerant will result in lower temperature.  It will continue to lower the pressure and temperature in the evaporator until it reaches 32 degF or lower.  Once the evaporator temperature reached 32 degF or lower, the moisture on the coil will freeze.

This is not the case of a plugged condenser coil.  It will result in higher discharge pressure resulting in higher amp draw.

Ken

[Ray,IN]

I agree with Ken; insufficient air flow caused the condition. Running the fan on the low setting in those weather conditions can cause this to happen too.

The thermostat temperature setting has nothing to do with the coils freezing over.

[whj469]

I have been told that about 21 degrees F less then outside temp. is all you can expect? Not different then a home AC.

[Kirk W]

1 hour ago, whj469 said:

I have been told that about 21 degrees F less then outside temp. is all you can expect? Not different then a home AC.

Today the outside temperature here was 102. My air conditioner was cycling normally, starting at 76° and shutting off at 74°.  The one in the RV works just as well. 

Edited September 5, 2021 by Kirk W

[TXiceman]

1 hour ago, whj469 said:

I have been told that about 21 degrees F less then outside temp. is all you can expect? Not different then a home AC.

This is some internet misinformation.  When the A/C is operating as designed, you should have 20 degF (+/-2 degF) between the air entering the unit and the out let of the unit...both as close to the unit as possible.  Use only a thermometer, not an infrared temperature sensor.   

Ken

[Rotorhead]

This is all great information. Thanks to all I really appreciate it.

I was thinking of the situation and thought I'd share as it may be relevant.

We were setting up around dinner time. I was outside doing all the hook ups etc... My wife was trying to cook some dinner. She said the stove isn't working. So I turned the gas on and went about my business. After a bit I smelled gas. So I went inside and it was very strong. They all said they couldn't smell it. I guess she decided to microwave hotdogs instead of using the stove and had left the knob on LO. Anyway, I got them out and opened the windows to air it out. We went down to the beach for a while. Of course I forgot to turn the AC unit off.

Is it possible that that made it freeze up? Unit running, windows open, hot and humid?

Chuck

[Kirk W]

3 hours ago, Rotorhead said:

Is it possible that that made it freeze up? Unit running, windows open, hot and humid?

Not only possible, it sounds probable if everything has been working well since. 

[Rotorhead]

Thanks Kirk.