Air conditioner won’t stop running

[Rotorhead]

Hello All,

What can cause an AC unit to continuously run other than having the fan in low or hi? It has been freezing up here and there. I fixed some leaks between then input and output side. Of course I don’t think that’s going to make it run non-stop. 
Is there a component up on the unit that might need replacing? I have already put a new thermostat and freeze sensor that goes into the evaporator.

Chuck

[TXiceman]

First and obvious question is....Did it do this before and after the new thermostat?   Have   you traced the signals to the roof and see where the power is applied to on the control board?  

 

Ken

[Pat & Pete]

The relay on the control board has maybe gone bad . 

Pretty cheap ( about 10 bucks ) and easy fix if you're decent with a soldering iron .  

Or , just replace the board for a pocket full of money . 

[Wrknrvr]

If it is a Dometic thermostat, try and reset it. Not sure if that work help or not.  It could be a sensor if that unit has other Ac units hooked to the same thermostat.

  Post a picture of your thermostat 

[Rotorhead]

4 hours ago, TXiceman said:

First and obvious question is....Did it do this before and after the new thermostat?   Have   you traced the signals to the roof and see where the power is applied to on the control board?  

 

Ken

It did it before the new thermostat as well

[Twotoes]

Is your thermostat set to auto? If it is set on fan (hi or low) it will continue to run. If set on auto it will stop when it reaches the temperature you set. Don't ask me how I know, lol.

[Rotorhead]

41 minutes ago, Wrknrvr said:

If it is a Dometic thermostat, try and reset it. Not sure if that work help or not.  It could be a sensor if that unit has other Ac units hooked to the same thermostat.

  Post a picture of your thermostat 

Dometic LCD

[Rotorhead]

10 minutes ago, Twotoes said:

Is your thermostat set to auto? If it is set on fan (hi or low) it will continue to run. If set on auto it will stop when it reaches the temperature you set. Don't ask me how I know, lol.

Ok thanks. I’ll give it a try.

[Rotorhead]

10 minutes ago, Twotoes said:

Is your thermostat set to auto? If it is set on fan (hi or low) it will continue to run. If set on auto it will stop when it reaches the temperature you set. Don't ask me how I know, lol.

Ok thanks. I’ll give it a try.

[Wrknrvr]

  Do you have more than one Ac unit on the rv.

  What thermostat did u replace. We need a picture of it or one like it.

  Did you do the initial setup when u installed the new thermostat. On the installation manual that came with the thermostat there should be instructions for to do the initial installation.

 

 

  

[Wrknrvr]

  Sorry for the delay on this post. I apparently did not hit the post button yesterday.

 

   Did you replace the thermostat with the same kind.

 

  If you replaced a 4 or 5 button older style thermostat,      It has to have the proper control board replaced on the side of the Ac unit on the roof. And if you have more than one Ac unit, then you need to replace every board with the proper one , so they will work with the new thermostat.

[Rotorhead]

On 4/13/2022 at 9:04 AM, Wrknrvr said:

  Do you have more than one Ac unit on the rv.

  What thermostat did u replace. We need a picture of it or one like it.

  Did you do the initial setup when u installed the new thermostat. On the installation manual that came with the thermostat there should be instructions for to do the initial installation.

 

 

  

I only have the one unit.

[Wrknrvr]

Did your old thermostat look like the new one you installed 

[Ray,IN]

Some rooftop units will run the fan continuously and switch the compressor off/on as required to maintain temperature.

[Kirk W]

14 hours ago, Rotorhead said:

I only have the one unit.

Is this an RV that you have had for a while and the A/C used to work properly but this spring stopped, or might this be a new to you RV?

[Rotorhead]

21 hours ago, Wrknrvr said:

Did your old thermostat look like the new one you installed 

I replaced it with an exact match.

[Rotorhead]

7 hours ago, Kirk W said:

Is this an RV that you have had for a while and the A/C used to work properly but this spring stopped, or might this be a new to you RV?

We’ve had this for about a year and a half now. It’s a 2017. It only had about 4,400 miles when we got it so I think it sat for most of its life until we got it. The first few trips it was pretty cold. Then it changed. 
I just checked the output temperature and it is only about 8-10 degrees cooler than outside temperature. 
The thermal overload protector was pretty hot. I don’t know if that’s normal or not and didn’t test resistance yet. 
This last trip I finally got an error code on the thermostat. “E1”. Some sort of communication error. Maybe the control board?

[Ray,IN]

4 hours ago, Rotorhead said:

We’ve had this for about a year and a half now. It’s a 2017. It only had about 4,400 miles when we got it so I think it sat for most of its life until we got it. The first few trips it was pretty cold. Then it changed. 
I just checked the output temperature and it is only about 8-10 degrees cooler than outside temperature. 
The thermal overload protector was pretty hot. I don’t know if that’s normal or not and didn’t test resistance yet. 
This last trip I finally got an error code on the thermostat. “E1”. Some sort of communication error. Maybe the control board?

The Delta/ difference between chilled air and intake/return air should be 20°F or a bit more. The ambient temperature of air outside the RV is immaterial.

[Wrknrvr]

  You may need to do the initial setup.  That is if it was not done when you put the new thermostat on.

  You should have a paper instructions that came with the new thermostat. If not you should be able to get it online. 

   With that done, see if it registers correctly.

 

  On some Dometic thermostats you had to do a reset occasionally to keep them working properly.

[Rotorhead]

29 minutes ago, Ray,IN said:

The Delta/ difference between chilled air and intake/return air should be 20°F or a bit more. The ambient temperature of air outside the RV is immaterial.

Oh. Ok thanks. I didn’t know that. I thought it was the outside. I will have to take the measurements on the next warm day and when I have a day off. 
I start my week on hitch tomorrow.

 

48 minutes ago, Wrknrvr said:

  You may need to do the initial setup.  That is if it was not done when you put the new thermostat on.

  You should have a paper instructions that came with the new thermostat. If not you should be able to get it online. 

   With that done, see if it registers correctly.

 

  On some Dometic thermostats you had to do a reset occasionally to keep them working properly.

I’ll have to look for the manual online. I am sure I tossed it. So much for the plug and play days eh?

I did pull the styrofoam cover off after it had been running for a while. It had a little bit of frost along the top and a little along the bottom. Not enough to be frozen up.

 

[Kirk W]

6 hours ago, Rotorhead said:

I just checked the output temperature and it is only about 8-10 degrees cooler than outside temperature. 

The way to check for proper cooling from the air conditioner compressor is to use a good thermometer(I recommend a dial type as available on Amazon) and measure the air temperature at the inlet to the cooling coils, then record that temperature and move the thermometer to the exhaust side of the cooling coils and measure it. The service manual recommends that the temperature be lowered by 18° to as much as 24° but no more as too much can cause a freeze up tendency as too little means the compressor isn't at full capacity or refrigerant may be low. They also say that service is required if the temperature change is less than 16°. 

While the outside temperatures do impact the interior temperatures the ability of the air conditioner to cool the RV is impacted by many things besides the air conditioner's operating. RVs then to not be the best insulated so heat gain from direct sun is far greater than in a house and there also is usually more hot air intrusion as well. Also things like dual pane or single pane windows make a big difference. But none of this really is likely to have much to do with the blower running all of the time, even if the inside temperature has fallen to or below the thermostat set point. Is it safe to assume that the blower does stop if you turn off the air conditioner?

[Rotorhead]

10 hours ago, Kirk W said:

The way to check for proper cooling from the air conditioner compressor is to use a good thermometer(I recommend a dial type as available on Amazon) and measure the air temperature at the inlet to the cooling coils, then record that temperature and move the thermometer to the exhaust side of the cooling coils and measure it. The service manual recommends that the temperature be lowered by 18° to as much as 24° but no more as too much can cause a freeze up tendency as too little means the compressor isn't at full capacity or refrigerant may be low. They also say that service is required if the temperature change is less than 16°. 

While the outside temperatures do impact the interior temperatures the ability of the air conditioner to cool the RV is impacted by many things besides the air conditioner's operating. RVs then to not be the best insulated so heat gain from direct sun is far greater than in a house and there also is usually more hot air intrusion as well. Also things like dual pane or single pane windows make a big difference. But none of this really is likely to have much to do with the blower running all of the time, even if the inside temperature has fallen to or below the thermostat set point. Is it safe to assume that the blower does stop if you turn off the air conditioner?

Awesome information Kirk.

Yes, the blower does stop when the system is turned off. If I adjust the temperature up some from say 72 to 75, it seems to cycle on and off as you would expect it too. 

Thanks again.

[sheldons65]

We ended up getting two of these and have been very happy. They are a little pricey but super easy to install. We love how they work and much better than the Dometic one. It does a much better job of control. Plus we can control the thermostat over the internet and via Bluetooth. 

[johnSm]

May be issue is in thermostat