Dash Air Thoughts and Information

[beltguy]

Wayne Schell and I have been discussing the dash air details for his new bus. He and I thought you might want to see some of the information.

I am starting this thread to discuss both AC hardware AND AC charging (Wayne obtained a great chart that simplifies charging - both Freon and oil)

So, lets start with the hardware side first. We are both using Red Dot dash units. I am using a Red Dot 5045 (see photo and detail PDF attached). He is using roughly the same version but not the "back wall" model. Note that these units rated at 44K BTU heating and 33K BTU cooling. That cooling rating is the equivalent of two roof top units in terms of BTU ratings.

RedDot R-5045.jpg (15.65 KiB) Viewed 3443 times

Red Dot 5045.pdf

(328.43 KiB) Downloaded 565 times

I have had my system installed for a bit less than 10 years. It has done a fantastic job and we have not encountered a situation where we needed to fire up the generator and run a roof air. When I installed my unit I did the typical posting on various bus forums and there were many folks who said I would have problems with "pooling of oil" in the system due to the various "dips" in the plumbing. So far that has not been a problem. You can see a bit more detail on my system on my project pages: http://beltguy.com/Bus_Project/busproject6.htm

In the next day or so I will post and discuss the charging document.

Jim

[luvrbus]

That is strange Jim I just finished my Ac and heat using the OEM dash unit I was lucky it was still there but Welch told me to make sure and have a dip or trap for the oil.I used a 10 cylinder Airsource 5899 compressor Welch told me to use, it works you can make ice cream but it was expensive for a compressor.I did buy a Red Dot remote condenser and ended up not using it I have so much room in the CAC and radiator compartment I had plenty of room to mount a regular condenser

[beltguy]

I am beginning to recall that previous Dash Air threads were a bit like discussions on Oil -- lots of opinions In this case, that is a good thing. There are lots of ways to get the job done.

Clifford, your compressor looks like it has a displacement of about 15.6 Cu Inches which is huge. I used a "York Style" two cylinder compressor (Climate Control ET-210L-25150) which has a displacement of about 10.0 Cu Inches. Obviously your compressor will be much smoother running. I chose the CCI compressor simply because that was the style/mounting that was on the Series 60. I did replace the compressor and chose the largest displacement model. I was not concerned about vibration on that engine that far back in the bus.

I checked the displacement required by the 5045 and Red Dot is not all that clear. They say to look at the 75S series compressors and that is actually several different compressors. It looks like they vary in displacement from 5.3 to slightly less than 10.

Interesting comment about the "trap" for the oil. After all the "discussions" about the perils of oil being trapped in the threads of about a decade ago, I finally reasoned that ALL AC systems have significant "elevation changes, any of which could trap the oil.

I have "thrown" several AC systems together on various vehicles and they do not seem to be nearly as critical as the "experts" would have you believe. Perhaps "cobbled" would be a better description . Maybe I have just been lucky.

Jim

[rusty]

I am using a sanden model 4417 compressor family SD7H15. This is the compressor that came on the engine I have. Clifford is there anyway you can post how an oil trap works and what it looks like. That way if anyone wants to put one in they will know how. As of now I don't think I will put one in the system. It does make me think about it as my condensor is at a lower level than my compressor and the evaporator. Does anyone know how the oil in the system works? I would guess that the oil is in the system to protect the compressor. In my system the discharge in from the compressor raises about 6 inches before it falls to the condensor. Is that enough of a trap to let the oil to migrate back to the compressor or do I have it all wrong?

Wayne

[beltguy]

After you decide on the hardware you are going to use (including the hose and coupling system), the next big challenge is how to charge the system (assuming you are going to do it yourself).

Before you actually add the Freon/oil you need to evacuate the system. That is a pretty straight forward process. Most folks recommend at least a 30 minute application of vacuum to make sure any moisture has been removed. I usually go for an hour. At the end of this process is when you let the system set with the vacuum pump off and watch to make sure the system is not leaking (vacuum drops).

Charging the old R12 systems was easy. Most folks used the "watch the bubbles" process.

For 134, every textbook/site I have seen says you "must" use the "weight scale" process (determine charge by weight of the r134 injected into the system). That is easy for a standard application that has been evacuated. Every modern car will have a specification for the 134 charge weight.

But what do we do with our custom built system with roughly 100 feet feet of hose/tubing? The supplier that Wayne is working with gave him the attached chart. I think it is a great reference chart!

Air Conditioning Charge Chart.pdf

(149.19 KiB) Downloaded 527 times

In my next post I will discuss how I charge a system without using scales.

Jim

[beltguy]

Well, I guess I should spend more time reading what I attach

I re-read the charging sheet I attached in the above post, and found that it contained both charge processes - by weight and by pressure. Most sources do not list the pressure method, even though it is commonly used by most AC technicians.

I have done my charging by the pressure and "feel" method. I have used a chart similar to the pressure/temperature chart in the previously attached document. As I am adding the charge, I watch both the low and high side gauges and at the same time place my hand on the suction tubing going into the pump. As the tube starts getting cold, I slow the charge rate and watch the gauges for stabilization.

I don't pretend that I am an expert. I would love to have others add their thoughts.

Jim

[luvrbus]

I used the temperature with high and low pressures to charge mine.The problem I had was figuring out the OCR the ratio of oil to Freon of 3.3 to 8% by weight .I believe I found the chart for calculating extra oil for the long piping on a Sanden site.I have maybe 20 ft of hose total my copper tubing was in place and insulated with the dip already in the suction line so I used it .The dip is supposedly a safety factor of 1 oz of oil I was told by more than 1 AC person then others say no dip