Community Forums

1peddler · 02-06-2013, 03:18 PM

When we turn on our dash air, it will cool for 20 to 30 minutes. Then it will blow warm to hot air. If we turn it off for 30 to 45 miniutes and back on it will cool again for another short time. Any thoughts why this is happening?

SteveS · 02-06-2013, 04:12 PM

One of the most common causes for the indications described is that the evaporator freezes up and will not let air pass through...to supply cold air. Air being blown in under these conditions is not cooled because heat is not exchanged through the evaporator. This is frequently caused by an improper freon charge in the system (usually too low because the system may have leaked a little refrigerant over time). R134 has a narrow operating range compared to the old R12 and is more difficult to properly charge systems. The reason it cools again down after awhile is that the ice has melted from the evaporator and allows air to pass through once again.

bluepill · 02-06-2013, 04:43 PM

Steve's post is a good possibility. Evap. freezing means that the temp. goes below 32 degrees. The optimum temp. at the evap core is a few degrees above freezing. If you test the dash vent outlet temps and find them below 40 degrees, freeze-up is a good possibility.

Another thing that can give your symptoms is a weak clutch on your compressor. As it heats up from use, it stops engaging. If you can visually check the clutch, you can see if that is happening.

Good luck.

Algoma · 02-06-2013, 05:17 PM

If you haven't got the equipment you need to go to an A/C shop and have them check the high and low pressures in the system. You may have too much or too little Freon in the system.

EngineerMike · 02-07-2013, 07:24 PM

On our rigs can also be a vacuum problem where the dash air selector doesn't hold its selection. I have this or a similar problem, when the cooling runs out (heat never does), I can turn the switch off then back to AC and cooling comes right back. Sort of like rebooting a computer.
Not sure how to solve that. Its on my list. Which isn't short.

Family Man · 02-08-2013, 08:48 AM

You have a list??? I'm afraid to make a list. The cost of the ink and paper alone would likely break me...

rbguinn · 02-11-2013, 11:45 AM

Solving air conditioning refrigeration problems is like going to the doctor. One or more problem may exist.

The unit may simply be low on freon which can cause part of the evaporator to freeze up and cold air stop. This is the most common problem. The expansion valve is not able to do its job without the proper level of refrigerant. Go to a automotive shop and buy a combo that will allow you to put freon in your system and a gage that will tell you if you are low on freon. The low side connector is on the exterior firewall area and the low side connecter is where refrigerant is added. Add freon until the gage reads you have the correct amount of freon. That may solve your problem. With the amount of refrigeration hoses in motorhomes, a small leak is common. Currently, I add a can of freon about every two years. I doubt I can find a leak this small!

The expansion valve may be defective. When you turn on the dash air, the expansion valve opens to its capacity to as quickly as possible pull out the calories inside your coach. As the inside of your coach cools, the expansion valve restricts the flow of freon resulting in a colder outcome as the liquid refrigerant expands quicker in the evaporator with less freon allowed to flow into it. If the refrigerant level is good, anything outside this function, the expansion valve most likely needs replacing.

Another possible problem is the system may have moisture. If not properly evacuated to remove all moisture after the system is open, moisture can be present in you freon. The moisture if not caught in the dryer, may freeze up at the expansion valve stopping the flow of refrigerant. If you have not had any work done to your dash air system that include unscrewing hoses in history, then moisture may not be your problem.

Someone else touched on a problem with the compressor clutch. The greatest load on a compressor is when it is first turned on. Slipping can be heard and visually seen and sometimes smelled. This condition will get worse with system use. Sparks can ultimately fly from a compressor clutch as it scrubs metal to metal and the compressor will not longer turn.
Good luck in establishing your solution.