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Old 07-21-2022, 08:49 PM   #1
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THOR #25110
AC doesn't cool at freeway speeds

The shop that works on my cars agreed to look at the dash AC on my 3401 today. I had put too much freon in it so he got the charge right. Parked and running at fast idle it was about 40 degrees discharge temperature at the center duct. I test drove it about 10 miles on the freeway and the outlet temperature slowly went up to 60 degrees. When I slowed down and stayed on the frontage roads going back the temp started going back down. Again parked with the engine on fast idle it dropped to the low 40's.

Any idea what could cause this. He ran it at 1500 RPM when I got which is about the engine speed on the freeway and it cooled OK. (I'd live 35-38 degrees like my car but I can live with 40-42).

Thanks

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Old 07-21-2022, 11:58 PM   #2
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Just a WAG here. I think vacuum decreases with engine loading so perhaps when you are loading the engine actually driving on the freeway (especially going up a hill) vs sitting in your driveway, the engine vacuum drops and that may be enough to affect the vacuum operated blend door in your dash A/C unit (or a vacuum motor, etc.). Maybe a deteriorating or leaking vacuum hose connection somewhere or leaking vacuum check valve. If the hill is a long one you might experience a temp shift in the coach depending on outside air temp etc. I would also expect coasting down hill (throttle body closed) would raise engine vacuum and cooling would return to "normal" if there were no leaks. Not sure if there is a vacuum reservoir on these coaches.
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Old 07-22-2022, 12:14 AM   #3
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Iím not sure what operates the doors on this AC because the engine is diesel so thereís no engine vacuum. The fresh air doors are right on the front of the evaporator and I have thought about taping them closed.
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Old 07-22-2022, 12:28 AM   #4
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Guess I should have looked a little closer at your coach info. A vacuum pump on the diesel maybe? Sorry not familiar with your dash A/C controls either so I will bow out for those that would know your coach details better than this gasser does.
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Old 07-22-2022, 12:42 AM   #5
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Was this on recirculate? I would imagine a fresh air mix at 90+ degrees at highway speeds could dilute that cooled air.
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Old 07-22-2022, 01:30 AM   #6
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Yes. I keep it on recirculating
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Old 07-22-2022, 01:55 AM   #7
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It almost sounds like the compressor is turning off when the engine is under load. I can remember some A/Cís doing this to conserve fuel back in the day.

I seriously doubt that is whatís happening but there may be a relay that is only intermittently working and causing the compressor to turn off randomly at times.

I have a 2002 Lexus that started doing this a couple years ago. After doing some online reading and troubleshooting it turned out to be a bad relay. I picked one up at the auto parts store for $20 and replaced it. It has been working fine ever since.
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Old 07-22-2022, 03:33 AM   #8
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I have noticed the same thing at speed in our 3901. But I have found that it works fine when the fan is on the fastest 2 speeds. Ours also works at all speeds on recirc. I think it is air pressure in the generator compartment closing the intake door when not on recirculate, but not absolutely positive.
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Old 07-22-2022, 10:40 AM   #9
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Originally Posted by ChiefBob View Post
Iím not sure what operates the doors on this AC because the engine is diesel so thereís no engine vacuum. The fresh air doors are right on the front of the evaporator and I have thought about taping them closed.
My Coach uses a vacuum pump for the controls
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Old 07-22-2022, 04:09 PM   #10
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My first thought was at highway speeds the pressure might be getting too high which would cause the compressor to shut off unit the pressure is reduced which could be 5-10 seconds later and then the compressor is back on, then back off..... I'm no HVAC mechanic but my understanding of the AC system thinks this is possible.
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Old 07-22-2022, 08:56 PM   #11
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Originally Posted by ChiefBob View Post
The shop that works on my cars agreed to look at the dash AC on my 3401 today. I had put too much freon in it so he got the charge right. Parked and running at fast idle it was about 40 degrees discharge temperature at the center duct. I test drove it about 10 miles on the freeway and the outlet temperature slowly went up to 60 degrees. When I slowed down and stayed on the frontage roads going back the temp started going back down. Again parked with the engine on fast idle it dropped to the low 40's.

Any idea what could cause this. He ran it at 1500 RPM when I got which is about the engine speed on the freeway and it cooled OK. (I'd live 35-38 degrees like my car but I can live with 40-42).

Thanks
Hello sir and sorry for your troubles. If the a/c is operating properly at idle I would look at the fan clutch as there could be a problem with the clutch controlling the fan. Not really familar with your set up but if it's running good at idle and your driving down the road and it warms up and your mechanic is sure they have the charge right then I would look at the fan control that sucks air thru the condensor. It is either electrically controlled or hydraulic, and should be 2 speed control for just this purpose. Car a/c and diesel pushers are two totally different things. Especially when talking about a/c. Also keep in mind that if the freon charge is off there are sensors installed in the system that will shut the compressor off if it exceeds or drops below minimum pressures. Obviosly there is a leak in the system as with most diesel pushers because there are a lot of lines that could potentially leak and the fact that you had stated you over filled the system. Take it to a proffesional who deals with diesel pushers and I'm sure they will find the issue. I always measure the amount of freon I add by using scales to prevent over charging. Good luck and hope this may help some
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Old 07-22-2022, 09:49 PM   #12
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Thanks. I wish I could find a place that is good with diesel pusher AC. I would gladly pay to have it work right.
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Old 07-23-2022, 03:29 PM   #13
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i run my dash air at the MAX setting to prevent the circulation vent form opening. that alone will keep temps cooler at the center


i would also look at the electric fan on the condenser up front on one side of the generator and see if it cycles on and off as needed when you are running at fast idle to test system


i would add ...my tuscany dash air has been a pita since new
new everything, and it will charge and be freezing cold air and then 2 weeks later losses enough freon to stop working. i have vac and pressure checked for 24 hrs at a time and it is leak free. but then it looses charge.




our chassis take a lot of freon to work. its nearly 80 feet of hose .



you can also under the front hood tape over the fresh air damper and it will not allow any outside air in. dont know why they build them that way, its a big hole for dirt and stuff.



its all basic stuff under there, any good ac shop should be able to look at it.
the compressor on the engine is a bit tricky to remove but its easy to find for replacement.



your engine should not be cutting off compressor at highway speeds, if it is..it most likely low on charge and not cuttign off, but not having enough refrigerant to pump up
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Old 07-23-2022, 04:01 PM   #14
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Originally Posted by powerboatr View Post
i run my dash air at the MAX setting to prevent the circulation vent form opening. that alone will keep temps cooler at the center


i would also look at the electric fan on the condenser up front on one side of the generator and see if it cycles on and off as needed when you are running at fast idle to test system


i would add ...my tuscany dash air has been a pita since new
new everything, and it will charge and be freezing cold air and then 2 weeks later losses enough freon to stop working. i have vac and pressure checked for 24 hrs at a time and it is leak free. but then it looses charge.




our chassis take a lot of freon to work. its nearly 80 feet of hose .



you can also under the front hood tape over the fresh air damper and it will not allow any outside air in. dont know why they build them that way, its a big hole for dirt and stuff.



its all basic stuff under there, any good ac shop should be able to look at it.
the compressor on the engine is a bit tricky to remove but its easy to find for replacement.



your engine should not be cutting off compressor at highway speeds, if it is..it most likely low on charge and not cuttign off, but not having enough refrigerant to pump up
Luckily, I have never had to add freon nor have had any issues at all, and it produces very cold air. I always push the recirculation button, so it is lit up and that keeps the outside air vent from opening. Then we tend to run on the third speed to keep the fan noise down a bit.

Keeping the outside air vent is important and checking to be sure no hot water is leaking through the closed heat valve is important as well. That could be an issue with higher speed warming or failing to cool.
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Old 07-23-2022, 06:41 PM   #15
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Thanks all. I had my very good AC man get the charge right but his expertise is cars so admits he is at a loss on this scenario. He wonders if the condenser in the front is not getting good air flow when driving at higher speeds. I thought about fabricating some sort of air scoop on the bottom to direct air up there.

I don't know how to determine is the compressor is cycling off at high speeds. When parked and the RPMs set around 1500 is still seems to cool OK, although I would really like lower than 40 degrees.

The AC components are made by Comfort Aire so I plan to call them next week and see what they say. My questions to Thor were answered with "call Comfort Aire.
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Old 07-23-2022, 09:30 PM   #16
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Thanks all. I had my very good AC man get the charge right but his expertise is cars so admits he is at a loss on this scenario. He wonders if the condenser in the front is not getting good air flow when driving at higher speeds. I thought about fabricating some sort of air scoop on the bottom to direct air up there.

I don't know how to determine is the compressor is cycling off at high speeds. When parked and the RPMs set around 1500 is still seems to cool OK, although I would really like lower than 40 degrees.

The AC components are made by Comfort Aire so I plan to call them next week and see what they say. My questions to Thor were answered with "call Comfort Aire.
your condenser should have a BIG electric fan on it, road speed is not dependent on proper working order
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Old 07-23-2022, 11:33 PM   #17
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Mine is like that
Maybe a relay or power issue but exactly, should run if on
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Old 07-24-2022, 12:04 AM   #18
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When a person is driving at highway speeds the fan isn't necessary
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Old 07-24-2022, 12:04 PM   #19
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When a person is driving at highway speeds the fan isn't necessary
So, is there a pressure or temperature sensor?

Will look at mine closer
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Old 07-24-2022, 12:15 PM   #20
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So, is there a pressure or temperature sensor?

Will look at mine closer
Most vehicles ac fans turn on when the ac is turned on, only the engine fans an cars usually turn on by temperature. I was just saying the amount of air going through the condenser at highway speeds should be adequate
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