ac temp.

As usual there is a lot of confusion on how a RV air conditioner works. It is simple the inside air is pulled through the return, cooled by the evaporator coil and then returned through the discharge outlets. It is the SAME air only cooled. There should be somewhere around a twenty degree difference. If the inside air is 100 then the discharge will be somewhere near 80. As the inside temperature falls to say 80 then the discharge will be bear 60 maintaining the same difference. It is not complicated.

wa8yxm wrote:
To fully and properly test teh operation of an air conditioner you need to know several things

1: Indoor temp (at the intake)
2: Outlet temp indoor
3: Outdoor temp (At the intake)
4: (in case you have not yet guessed) Outlet temp (outdoor).
5 Humidity, indoor and 6 outdoor.

Then you need the charts from the maker, or the computer program.

Source, all the books on Air Conditioning both automotive and home that I've ever read agreed on all but Humidity. SOME included that.

You do NOT have any outside air to inside at all on RV AC units---SAME with residential. You DO have outside to inside on Automotive.
There are NO charts and NO "supercool" procedure on RV AC units. ALL RV AC models with the same model number use an EXACT charge of coolant. Usually around 1 lb, give or take a few ozs. The exact Coolant charge is on ALL the spec plates on the RV AC unit. The REASON they have exact charge is because all of the same model have the exact same size lines and system components, unlike residential or commercial systems. The temp differential is for novices as there are a number of factors that can cause a wide swing on a perfectly good AC unit--how well the intake to exhaust plenum is sealed and the ductwork is sealed. The ONLY true valid test of performance on a RV AC unit is the compressor amp draw with a temp corrected amp reading. It is based on 95 degree ambient and you subtract 1 amp for each 10 degrees below 95 ambient and add 1 amp for each 10 degrees above 95 ambient. You CANNOT read Home and Automotive manuals and then think you know RV systems. Doug

wa8yxm wrote:
To fully and properly test teh operation of an air conditioner you need to know several things

1: Indoor temp (at the intake)
2: Outlet temp indoor
3: Outdoor temp (At the intake)
4: (in case you have not yet guessed) Outlet temp (outdoor).
5 Humidity, indoor and 6 outdoor.

Then you need the charts from the maker, or the computer program.

Source, all the books on Air Conditioning both automotive and home that I've ever read agreed on all but Humidity. SOME included that.

No you don't. I'm assuming you are calling indoor temp the return air temp and the outlet the discharge air.
1&2, yes, that's how you determine the split across the coil.
3. Not sure what you are trying to say by outdoor temp at the intake, since no outside air is drawn inside. Outside temp does not affect operation, however, the correctness of the freon charge can be determined by using a clamp on mater to measure current.
4.Again, outlet temp?? No air is discharged outside.
5&6. Humidity has no affect on Delta T. The entire refrigerant circuit is sealed.

Charts from the maker??? What in the world are you talking about? Many of us diagnose air conditioners every day using a set of gauges and a thermometer. I have never heard of any manufacturer specific "charts". You don't even need the P/T charts from the refrigerant manufacturer to troubleshoot one.

Like Bob said, you just cant compare auto a/c with home a/c.
Anyone who says different just doesnt know any better.
Home a/c is a ~20 degree split.

TT roof air is also a bigger split than home a/c.

Auto a/c is designed to cool down to just above freezing at the evap and then cycle off from the low pressure cycle switch. This is due to some people living in more humid areas and we dont want the evpa turning into a block of ice, blocking airflow. Most cars with good running a/c should see ~40 +/- 5 while cruising down the highway.

I can get away with my adjustable cycle switch in my truck because we dont have any humidity most of the time. It can blow 25 degree air on high which means the evap is more like 18-20. In july-aug when its humid, I adjust up ~7 degrees.
ASE Master tech for 1/4 century, IMACA a/c certified so Im not just posting crap.

To fully and properly test teh operation of an air conditioner you need to know several things

1: Indoor temp (at the intake)
2: Outlet temp indoor
3: Outdoor temp (At the intake)
4: (in case you have not yet guessed) Outlet temp (outdoor).
5 Humidity, indoor and 6 outdoor.

Then you need the charts from the maker, or the computer program.

Source, all the books on Air Conditioning both automotive and home that I've ever read agreed on all but Humidity. SOME included that.

Bob Landry wrote:

Chris Bryant wrote:

marcsbigfoot20b27 wrote:
You guys saying 14-20 must be talking residential AC.
I just went out to my trailer 13,500 btu, ambient temp 74 F outside....important for condenser cooling.
Inside trailer 80 F. Turned AC on max, intake air at filter 74 (after 5 minutes) cold discharge air was 42 F. Switched to low fan, 38F. Both were dropping every minute.

That of course was at 8% humidity.

While the ultra low humidity plays a huge part, even with that a drop of that much indicates air recircualtion. The new R401 units average in the upper teens, older R22 units were 20. More if dry, less if humid.

Are the new RV units coming with R401? All I could find on R401 was that it is a blend used to retrofit R12 systems which would be refrigeration, not air conditioning applications. We're still on R410a with no relief in sight. I had a residential guy tell me he heard there is a replacement coming for R410a, but that was all he knew about it. It was really hard to get used to it after seeing the pressures that R22 runs at.

What Doug said- fumble fingers at work- it is R410a.

Bob Landry wrote:

Chris Bryant wrote:

marcsbigfoot20b27 wrote:
You guys saying 14-20 must be talking residential AC.
I just went out to my trailer 13,500 btu, ambient temp 74 F outside....important for condenser cooling.
Inside trailer 80 F. Turned AC on max, intake air at filter 74 (after 5 minutes) cold discharge air was 42 F. Switched to low fan, 38F. Both were dropping every minute.

That of course was at 8% humidity.

While the ultra low humidity plays a huge part, even with that a drop of that much indicates air recircualtion. The new R401 units average in the upper teens, older R22 units were 20. More if dry, less if humid.

Are the new RV units coming with R401? All I could find on R401 was that it is a blend used to retrofit R12 systems which would be refrigeration, not air conditioning applications. We're still on R410a with no relief in sight. I had a residential guy tell me he heard there is a replacement coming for R410a, but that was all he knew about it. It was really hard to get used to it after seeing the pressures that R22 runs at.

Should be R 410A. That is what Dometic and RVP are using and have for a few years. Doug

Chris Bryant wrote:

marcsbigfoot20b27 wrote:
You guys saying 14-20 must be talking residential AC.
I just went out to my trailer 13,500 btu, ambient temp 74 F outside....important for condenser cooling.
Inside trailer 80 F. Turned AC on max, intake air at filter 74 (after 5 minutes) cold discharge air was 42 F. Switched to low fan, 38F. Both were dropping every minute.

That of course was at 8% humidity.

While the ultra low humidity plays a huge part, even with that a drop of that much indicates air recircualtion. The new R401 units average in the upper teens, older R22 units were 20. More if dry, less if humid.

Are the new RV units coming with R401? All I could find on R401 was that it is a blend used to retrofit R12 systems which would be refrigeration, not air conditioning applications. We're still on R410a with no relief in sight. I had a residential guy tell me he heard there is a replacement coming for R410a, but that was all he knew about it. It was really hard to get used to it after seeing the pressures that R22 runs at.

I like to see a 18-20 degree split on my marine units. There's no reason to think it is any different on other types of equipment. Characteristics of air conditioner components do not change, and neither do the properties of rerigerant. Air conditioning isn't rocket science and you have a little wiggle room either way. If you stick a thermometer in the discharge grill you should see 56-59 degree and that's directly off the unit. If it's significantly lower, that's indicative of an airflow restriction. a higher split could be either low charge or the unit is simply undersized for the space. The latter is more likely as these are hermetically sealed units that hold about a pound of refrigerant, so if you get even a small leak, you'll probably lose the whole charge.

Automotive AC is different because they use R134a which has different properties than R22 or R410A, and you will see discharge temps in the 40's. You can't make a comparison between the two.

I have customers who argue up and down that their AC is working great because the discharge air is freezing. They don't notice that 2 feet away from the blower they feel nothing. I don't try to argue with them. I just let 'em sweat it out when the unit ices up.

beemerphile1 wrote:

marcsbigfoot20b27 wrote:
You guys saying 14-20 must be talking residential AC.
I just went out to my trailer 13,500 btu, ambient temp 74 F outside, important for condenser cooling.
Inside trailer 80 F. Turned AC on max, intake air at filter 74 (after 5 minutes) cold discharge air was 42 F. Switched to low fan, 38F. Both were dropping every minute.

That of course was at 8% humidity.

Car, RV, or residential doesn't make any difference.

You put a thermometer at the intake of the unit. Then put the same thermometer at the output. Normal is a 14 - 20 degree drop. This should be done after it has run for a while and temperatures have stabilized.

This statement just cant be true. My Tahoe blows easily 40 degrees below the inside cab air temp.....at least 40 to 50 less.
Like stated, my TT A/C blows colder also, though I will test again in the middle of a 100 degree day this weekend to see how much affect warmer weather has. I have a window unit I will try out tonight outside (no recirc influence for true reading).

I agree that home AC is 20 degree split.