Community Forums

bamaboy473 · 10-04-2018, 07:20 PM

My personal vehicles are 40-47 degrees when it's 87 outside. The MH just had a new compressor and dryer installed, but can't see less than 52 degrees up front in our DP.

Roof air at the same time is in the mid 40s, so what should be normal for our dash air? Is a low 50s reading as good as we can hope for?

Ambient air temp was around 85 degrees at the time, as I recall.

winniman · 10-04-2018, 08:26 PM

Pretty much. You cant expect the dash to cool the whole rv anyway. If its eighty five outside, you are in roof top air territory to keep the rv at a decent temp.

firedoc · 10-04-2018, 09:27 PM

Typically these a/c are doing good to expel are 20 degrees lower than intake air. Notice intake air is not the same as ambient temperature. Test the temperature at the intake and then at the closest vent. If you get about 20 degree drop it’s doing its job.

chunker · 10-04-2018, 10:13 PM

Remember that for a DP much of the air conditioning hardware is at the back and you will lose some cooling moving the freon to the front. If you have around 50 be happy.

lonfu · 10-05-2018, 03:13 AM

Working on various kinds of AC systems for 40 years or so. The air that is coming out of your center vent on a dp should be 38 to 42 degrees. If it isn't then there are several common problems that need to be looked at. the first most common one is the vent door that partially opens on "AC" setting. This door can be broken or stuck open. On "max AC" it should be closed. I've permanantly blocked mine off. Second thing is the "evaporator box cover" is leaking air. Instead of drawing inside coach air to cool, it is drawing outside hot air. I taped the edges of mine and then insulated the box with spray foam. Third, check your heater valve, they get stuck open as they age. If your heater core is hot and your AC evaporator is cold the resulting air can be warmer than you want. Lastly, I use a product called Enviro-Safe, it is a new coolant that will drop your AC system temp and reduce the cost of your coolant. Recent trip across the mohave desert at 110 degrees the interior of our coach to our bathroom was a comfy 77 degrees with just our dash AC running. yes, I have 38 foot DP. Don't expect a AC service guy to fix your "mechanical" problems, they only replace parts and charge the system. You'll have to do it yourself if you want results.

bamaboy473 · 10-05-2018, 05:34 AM

There's something, I think, because I just changed the compressor and drier and drew vacuum on the lines, but when I hook up the charging pump and set the dial to 85, the pointer comes to the line between Low and the Green area, and no more freon will go into the system.

Thoughts on that?

Gary RVRoamer · 10-05-2018, 05:50 AM

I'd say somewhere between 45 and 50 is common in a motorhome. The point about the intake air is a crucial one - since the coach is too big to cool with dash a/c alone, the air being circulated is always relatively warm. A car system has a much smaller air volume and the inside air begins to cool quickly, but an RV system simply cannot keep up and is always struggling to chill warm air.

I think the open air door problem is also common in motorhomes. I've had it on one of three coaches and have seen it in others. Perhaps because the HVAC system is sort of cobbled together and installed by less-than-expert workers. Have you tried running it on Max or Recirculate, which should close the outside door? Any difference?

Also had a problem with a previous coach where the heater valve that allows engine coolant to circulate did not fully close, so the a/c was always trying to overcome extra heat. A replacement heater valve solved that.

bamaboy473 · 10-05-2018, 09:45 AM

I should have stated interior conditions during the OP; apologies.

Our coach is at 77 all the time while parked, and the dash A/C is always on Max, so its recirculating 77 degree air.

Where would I find the heater valve; on the firewall up front, nears the dryer in the genset compartment, or next to the compressor in the rear?

lonfu · 10-06-2018, 07:27 AM

Quote:

Originally Posted by bamaboy473

I should have stated interior conditions during the OP; apologies.

Our coach is at 77 all the time while parked, and the dash A/C is always on Max, so its recirculating 77 degree air.

Where would I find the heater valve; on the firewall up front, nears the dryer in the genset compartment, or next to the compressor in the rear?

first, the only way to properly charge an ac system is by weight. Pressure is just a "tool" to make sure all the components are working correctly. Compressor making pressure, no plugged lines. I know you don't want to hear this but that is the way it is. If your gage is reading 85 on the low side then you are way over charged which will prevent the system from cooling correctly. If it is reading 85 on the highside then you are way under charged. Most DP's use about 4 lbs of coolant. yeah, that is a lot. Follow your heater lines from the engine to find your heater valve. Where it located depends on the year, the installer and the chassis builder. speaking generally, and I mean a real big generally.... low side should be 40 to 50 psi... this pressure depends on the ambient temp. could be as low as 35 and high as 60 depending on the ambient temp. (out side temp) Automotive AC is one of the easiest AC systems to learn, may I suggest that you pick up a book from the library study it out. If you do it will make sense on how it works and you will be able to trouble shoot it yourself. hope this helps....

Dutch Star Don · 10-06-2018, 10:59 AM

Like "lonfu" stated, the center A/C duct should be cycling between 38 and 42 when measured with an A/C temperature gauge inserted into that duct. Anything above 45 won't provide much cooling when the outside temp is above 90.

bamaboy473 · 10-06-2018, 01:33 PM

I have a guy that does household A/C systems. He told me to buy a guage set and a vacuum pump. I got the $17 vacuum pump that uses a compressor, but it wasn't perfect because he kept having to shut valves off while my pancake compressor cycled back up to pressure. That might have affected things.

If it's way overcharged, should we re-vacuum the system (I got a decent pump this time) and add freon? (there's a hand-written note that says, "2.8 pounds of freon") I guess we should try that and see where we are?

Waiter21 · 10-06-2018, 01:36 PM

If you are using the dash air, set it to recirculate. The air inside the MH will be cooler and less humid than the outside air..

harleyjt · 10-06-2018, 01:48 PM

Quote:

Originally Posted by Waiter21

If you are using the dash air, set it to recirculate. The air inside the MH will be cooler and less humid than the outside air..

Depends - it will be after the initial cool down. For initial cooldown, if mine has been sitting out in the sun all day, it may have interior temps of over 100. I usually open some windows, and turn on the fantastic fan and start the engine and run the A/C in normal cooling mode so its pulling in fresh air, rather than the existing hot stale air inside the coach. Once that hot stale air has been cycled out of the coach, then switch over to max A/C. I use the same approach in my car and truck. I might add that I installed a manual ball valve on one of my heater core lines to prevent flow through the heater core. This way if the water control valve isn't switching properly there is still no hot water to warm the air.
jt

bamaboy473 · 10-06-2018, 04:22 PM

For the OP, ambient inside air is 77, so dash air ought to have been in the 40s as has been suggested. I've done something wrong after changing out the compressor and drier, and the choice is to see what happens during our 2 week trip, or enjoy the weather forecast that temps will finally start to cool down in the SE!!