Community Forums

will stevens · 08-07-2015, 06:02 AM

I have a 2006 revolution on a Spartan chassis Driving down road with both coach a/c on it can get warm in cab on a hot day. My dash A/C will be 55 degrees at vent and climb to 60 then cool back down to 55. 95 degree day 1500 RPM I have put gauges on and high side runs up to 325 then the condenser fan steps up and pulls high side down to 250. This fan ramp up time is when vent temp goes up.
Low pressure is 28 to 33 depending where high side is. Compressor never turns off , only fan ramp up and extra cooling. All fins are straight and clean allowing for good air flow.
Spartan sent me info showing specs normal 134A readings 18-22 low, 160-240 high., High 350 +- 10 cut out, 250 +- 25 cut in. I assumed this was compressor cut out cut in but they say it is fan ramp up cut in cut out. (even then in and out seams backwards)
Was at service center and was told my system is operating to specs. Called Spartan with tech and they said it is normal. If you lower low side 18 to 22 it will not cool as well (65 degree vent tenp) and the condenser fan never ramps up.
Guess my question is this normal operation ?
I took it in thinking there was a restriction (previously changed dryer and expansion valve) in the condenser but I am told it is operating normal.

Triker56 · 08-07-2015, 07:30 AM

If 55º blowing out is normal. That sounds about right. What is your question?

To make it cooler inside. Run the generator and the roof AC's like everyone else does on real hot outside days.

dbywaters · 08-07-2015, 07:31 AM

my coach has an EVANS dash AC unit, probably similar to yours.

I would suspect the freeze protect thermal switch on the discharge of the evaporator. I had an AC that this switch failed and the Evaporator would freeze up which would cut down on air flow across the evaporator thus raising the discharge air temperature. This switch is in series with the dash AC switch and low pressure switch (thus turns off the compressor) I had to turn off the AC for a while until the ice melted and it would begin to work fine for a while longer.

There is a thermostatic expansion valve block mounted on the evaporator, yours sounds like it is ok...

The pressure switch on the high side compressor line (on my coach) is a normally closed switch, opens on high setpoint pressure. This switch controls my hydraulic fan speed (raising it to 100%) . On cooler days the low speed of the fan keeps the pressure down enough that the fan does not need to turn on.

I might be anal, but I installed an illuminated switch to interrupt power to the AC compressor, I tied it in series with the 12v circuit between the low temperature cutout thermostat and low pressure cut out. This allows the light in the switch to Illuminate only if the low temperature sensor allows the compressor to run. ALSO, on my coach the dash AC control panel calls for AC in almost every mode.. by using the switch I have full control of when the AC compressor can run, plus I have a light that turns on and off (even on the hottest of days) to reflect when the compressor is called to run.

I hope this gives you some ideas to what to look at again.

Doug

Nowabeachbum · 08-07-2015, 09:14 AM

Quote:

Originally Posted by will stevens

I have a 2006 revolution on a Spartan chassis Driving down road with both coach a/c on it can get warm in cab on a hot day. My dash A/C will be 55 degrees at vent and climb to 60 then cool back down to 55. 95 degree day 1500 RPM I have put gauges on and high side runs up to 325 then the condenser fan steps up and pulls high side down to 250. This fan ramp up time is when vent temp goes up.
Low pressure is 28 to 33 depending where high side is. Compressor never turns off , only fan ramp up and extra cooling. All fins are straight and clean allowing for good air flow.
Spartan sent me info showing specs normal 134A readings 18-22 low, 160-240 high., High 350 +- 10 cut out, 250 +- 25 cut in. I assumed this was compressor cut out cut in but they say it is fan ramp up cut in cut out. (even then in and out seams backwards)
Was at service center and was told my system is operating to specs. Called Spartan with tech and they said it is normal. If you lower low side 18 to 22 it will not cool as well (65 degree vent tenp) and the condenser fan never ramps up.
Guess my question is this normal operation ?
I took it in thinking there was a restriction (previously changed dryer and expansion valve) in the condenser but I am told it is operating normal.

Is this operating normally? Yes and no, the operating pressures seem pretty normal but the duct temperatures should be 45 to 50 degrees as a minimum. You should see a temperature drop of 25 to 30 degrees between the inlet air of the evaporator and the duct temp. I assume your condenser is located on the radiator. If it is, you have a switch that kicks on the fan when the head pressure gets too high. You have a low pressure switch for when you lose all your refrigerant, a high side for when the pressure reaches extremes(probably 450-500) and a pressure override to send a signal to kick the fan on because the pressures are getting too high. All of these switches control the compressor engagement. These pressure switches are sometimes 2 and 3 function switches in one, so don't look for 3 different switches. I assume that the override switch is what Spartan is talking about if so it has to be written backwards.(I guess it could depend on if the circuit is normally open or normally closed, so it could be just semantics)The fan cuts in at 350 to begin to cool down the condenser and out at 250. The compressor is cycled by low side pressure. I'm guessing but if your low side gauge is running around 20, it should kick out at 15 and back in around 30-35. That function is done by a thermstatically controlled switch that has its probe in the evaporator, sensing its temperature. A lower low side should always result in lower duct temperatures until it gets so cold that it begins to freeze the evaporator resulting in poor cooling.
It is very difficult to diagnose your system without more information like what is the history? Did it ever work better than it does right now? If it's new to you, what are other people seeing that have the exact same motorhome. Many motorhomes have similar systems but because they are applied differently, they do not have similar performance.
My diagnosis, and keep in mind you get what you pay for, would be:
Check charge, if proper and it hasn't been added to with some foreign refrigerant(not R134a). If someone added too much oil to the system, that would act as an insulator. Dump it and recharge.
Check the evaporator for good air flow. When they get dirty they lose effectiveness.
If the system has never been good, I would say the evaporator is bad, specifically one of the feeder tubes leading into the evaporator is clogged probably from manufacturing. Surprisingly it happens a lot.
Ultimately, perhaps the best thing to do is go to a reputable truck repair shop that specializes in air conditioning repair.

lllkrob · 08-07-2015, 04:58 PM

Yes, your system is operating normally. If you want the cab to be cooler, hang a pair of curtains behind the driver's/passenger's seats. This will block off the back end of the coach so the AC won't have to cool an area much larger than it's really designed to cool.

Texbeachbum · 08-07-2015, 05:07 PM

Quote:

Originally Posted by lllkrob

Yes, your system is operating normally. If you want the cab to be cooler, hang a pair of curtains behind the driver's/passenger's seats. This will block off the back end of the coach so the AC won't have to cool an area much larger than it's really designed to cool.

I did this and it really made a big difference. Where I live it is in the 100's now and my dash air cools good.

wa8yxm · 08-07-2015, 05:19 PM

The dash A/C is not nearly big enough on all Motor homes. This unit is designed to cool the cab of say a Ford F-350 Custom or such One bench seat, No back seat,, And you are trying to cool how many feet of motor home

Think of the windshield on that F-350 or even a semi truck, HOW MUCH Glass do you have up there...

No way can it keep you cool on a sunny day.

will stevens · 08-07-2015, 07:48 PM

I always run the generator and both coach a/c units

1ciderdog · 08-08-2015, 10:19 AM

Quote:

Originally Posted by will stevens

My dash A/C will be 55 degrees at vent and climb to 60 then cool back down to 55. 95 degree day 1500 RPM

I put a thermometer in a dash vent on my RV and I am getting consistent cold dash air at about 45 degrees. That was after adding a couple cans of Freon while traveling in Texas in June and it was hot outside. Could you be low on Freon? I did run generator and basement air much of the time on that trip.

Gary RVRoamer · 08-08-2015, 11:13 AM

I think your system pressures are around normal, but you should get colder air at the vents. I'm thinking you are getting a mix of chilled and warm air, bringing the outlet temps up somewhat. Are you running with the a/c in the recirculate (Max) mode? If yes, it still may be that the outside air inlet is not fully closed. There is also a mixing valve that blends heater air with a/c air to adjust the outlet temperature that may not be working properly. On a previous coach my heater was warming the air from the a/c because a heater valve had failed and didn't turn off. I was only getting 60 degree air from the a/c cause it had to overwhelm the heating system, even though I had dialed for maximum cooling and no heat..