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Old 07-28-2005, 07:56 AM   #1
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P-30 Dash Air Conditioner and "H" valve

Any body with a P-30 chassis having problems getting the dash Air Conditioner to cool way down?

I noticed that my AC would be very cold at engine startup (about 58 degrees). But when the engine got up to temp (around 210 degrees) the air coming from the dash air was getting warmer, (about 70-80 degrees).

So the first thing I checked was the refrigerant pressures and they were perfect.

Then I checked vacuum lines to the heater control valve.
My system controls warm air with an in line water control valve that is vacuum operated. There is a second valve inside of the heater box that is mechanically operated with bowden wire and linkage. Both valves were working properly.

I got out my P-30 manual and it speaks specifically to a known problem with this setup.

The valve is not very proficient and allows hot water to enter the heater core on a constant basis. The heater core is placed directly adjacent to the AC evaporator.

Since the two devices are in very close proximity, the hot water that is in the core is raising the temperature in the evaporator and consequently effecting the temp of the refrigerant.

The corrective action is purchase an "H" valve from ACME heating and Air onditioning Inc. This valve is placed in line with the supply and return hoses the heater core. The valve is also bridged between the supply and return hose. This valve allows you to block all water from entering the heater core and re-route the water through the rest of the system.
This valve also allows you to better adjust the temperature to the heater. Cost is about 40 dollars.
You can search ACME Heatinig and Air Conditoner and read about the H valve.
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Old 07-28-2005, 09:00 AM   #2
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Ken,
While my dash AC does not work at all (PO removed the condensor) I have dealt with the heater core by simply purchasing a plastic heater hose connector and removing the heater core from the coolant loop by connecting the inflow heater hose to the outflow. In the winter I switch it back again.

I think if you search on this you can see some pictures from John which show his setup using ball valves mounted to the firewall. Seems like with a trip to the plumbing department at Home Depot a manifold assembly could be devised inexpensively.
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Old 07-28-2005, 11:41 AM   #3
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Agreed

I agree that you could buy simple cutoff valves and or "loop" the hot water. I was actually going to do exactly that, install cutoff valves in both the supply and the return hoses. But when I researched the "H" valve and realized that the unit not only allowed me to divert the water, it is really intended to allow you to better mix the water and better balance the hot air being delivered when heating the compartment.

From what I understand, the existing valve is not very proficient and the user is constantly adjusting the temperature to offset the extreme operation of the existing valve.

I will try to scan the document that I am reading on this issue.

Did I mention that the "H" valve can be adjusted from inside the MH? Unlike a cutoff valve or loop installed under the hood. 39 dollars and I have corrected temperature variance of AC and I will be able to better adjust my Heat in the winter and I will be able to do it without lifting the hood.

See the H valve here http://www.acmeair.com/hwatervalve.htm
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Old 07-28-2005, 12:52 PM   #4
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More discussion

If you are interested in other discussion, this is a common problem with this type of A/C - Heater system.


http://www.openroadsforum.com/forum/...|ma{}/sr/1.cfm
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Old 07-28-2005, 01:05 PM   #5
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Yeah - that's the way to go. I think I have the same P30 manual and read the same thing after practically melting my legs off on a summer trip last year.

My dash control is shot so I did a "quick and dirty" fix. Someday when I'm not working on the Airstream I'll get around to fixing this. , replacing the condensor, etc.
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Old 07-31-2005, 08:48 PM   #6
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Ken- Thanks for the information. Winter is just around the corner and getting heat into our coach is an ongoing problem. I am going to study this and see if it will help us get more heat.
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Old 10-17-2015, 08:32 AM   #7
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Gentlemen
1. link to the above openroadsforum no longer connnects
2. looks like the name "acmeair" has been "highjacked' ?
I'm in the process of replacing the compressor and accumulator/filter on my 350LE but also feel that the hot air valve is leaking hot water into the under dash core?
As I live in Texas where winters are a joke, I would like to have the ability cut-off the hot water supply using Smily's H valve approach however I have been unable to source this component or how to install in an existing circuit?
Also, as I re-install the system and upgrade refrigerant to r134a and installation hints would be greatly appreciated. Thanks
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Old 10-17-2015, 10:31 AM   #8
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I'd stick with R12 and you'll be much better off. R134 is not a performance upgrade and the R12 is actually getting cheaper on ebay since nobody is using it. I just did my system (replace damaged hose, receiver/dryer, o-rings and expansion valve). Total cost, including 28oz of Freon with a 4oz dye and 4oz oil charge was around $160. Dash blows COLD air now. No need to flush and replace the system due to oil incompatibility either.

R134 is slotted to become unavailable soon as well.
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Old 10-17-2015, 10:56 AM   #9
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Quote:
R12 and you'll be much better off. R134 is not a performance upgrade
Absolutely true. There was a complete study done I read that described various coolant characteristics in AC units. The older coolants do better hands down. The newer ones require more effort- pressure, etc to give the same cooling ability which means higher power requirements, larger btu rating, etc. The change was simply an enviromental ruling.
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Old 10-17-2015, 04:13 PM   #10
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The only thing I know is that I can find any opinion I want on any subject on the Internet, from the informed to the opposite. Here is an original study that seems fairly definite in its assessment:

http://docs.lib.purdue.edu/cgi/viewc...05454873,d.dmo

It is entitled:
A Comparison Study of the Thermal Performance of R12 and R134a.

To clarify, this is the summarizing abstract of the results obtained:
The experimental results show that for almost all test conditions the R·134a operates with greater COP and cooling capacity. This is especially true of the system when charged with R·l34a where the condenser subcooling is 10 to 15 F (5.6 to 7.5 C). The effects of operating conditions on system ·performance are presented in detail. Several questions are considered through examination of the thermodynamic states at key points in the system. For example, it is shown how the system can operate at a higher pressure ratio with R-134a and yet have a greater COP. than for the system charged with R·12.

(COP stands for Coefficient of Performance and is defined as the ratio of the desired output to the required input.)
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Old 10-17-2015, 06:06 PM   #11
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Quote:
Originally Posted by chriscraw View Post
Gentlemen
1. link to the above openroadsforum no longer connnects
2. looks like the name "acmeair" has been "highjacked' ?
I'm in the process of replacing the compressor and accumulator/filter on my 350LE but also feel that the hot air valve is leaking hot water into the under dash core?
As I live in Texas where winters are a joke, I would like to have the ability cut-off the hot water supply using Smily's H valve approach however I have been unable to source this component or how to install in an existing circuit?
Also, as I re-install the system and upgrade refrigerant to r134a and installation hints would be greatly appreciated. Thanks

Chris... back to your original question: the ACME company still seems to be around, and I guess we're talking about one of the valves on this page:

Motorhome Dash AC and Heat systems

.... But does anyone know which is the valve in question?
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Old 10-18-2015, 11:13 AM   #12
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Quote:
Originally Posted by Punch View Post
The only thing I know is that I can find any opinion I want on any subject on the Internet, from the informed to the opposite. Here is an original study that seems fairly definite in its assessment:

http://docs.lib.purdue.edu/cgi/viewc...05454873,d.dmo

It is entitled:
A Comparison Study of the Thermal Performance of R12 and R134a.

To clarify, this is the summarizing abstract of the results obtained:
The experimental results show that for almost all test conditions the R·134a operates with greater COP and cooling capacity. This is especially true of the system when charged with R·l34a where the condenser subcooling is 10 to 15 F (5.6 to 7.5 C). The effects of operating conditions on system ·performance are presented in detail. Several questions are considered through examination of the thermodynamic states at key points in the system. For example, it is shown how the system can operate at a higher pressure ratio with R-134a and yet have a greater COP. than for the system charged with R·12.

(COP stands for Coefficient of Performance and is defined as the ratio of the desired output to the required input.)
Agreed that you can find all kinds of conflicting information on the NET but also understand that there is a lot of bias when it comes to many studies. Especially university studies and who funds them. Studies may obscure some of the fascist related to the subject in order to project a specific conclusion based on the premise of the study.

Note that COP is not the only defining limitation of a specific refrigerant and it's use. The systems that were designed for R12 were specified to operate with that refrigerant's characteristics. Condenser/evaporator size, compressor efficiency, expansion valve/orifice size and receiver/dryer medium are all considerations as well. Systems that were engineered to work specifically with R12 were sized according to that refrigerants characteristics. When changing over to R134a you're impacting all those components.

R134a also has a smaller molecular size and requires lined rubber hoses to properly contain the refrigerant. Systems must be properly flushed in order to remove mineral oils used in R12 systems and recharged with polyol ester oil. Looking on the NET you'll find those that have bypassed this step, but you never see follow ups from months or years later to determine longevity of the transition.

Not saying that R12 is better then R134a. Just saying that the use of a refrigerant in a system that was not designed for it can compromise the results. R134a being used in a system designed for R134a is as good or better then the systems using R12.

If you follow the history of the transition from R12 to R134a you'll find that it was more politically motivated then it was scientific. Dupont's patent on R12 was running out and they needed the standard to change in order to create a new refrigerant that had a new patent window and was designed specifically to be incompatible with the old refrigerant. In comes the EPA in bed with Dupont and history tells the story. EPA created the ban on R12 and Dupont created R134a. Win-win for both. Bad for the consumer.
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Old 10-18-2015, 12:38 PM   #13
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I put in a shutoff valve to make sure ac doesn't have to overcome engine heat, but in my research it is supposed to help by adding hot to the cool to condense the air vapor so that the defroster works better. My opinion is that ac cool is worth more than efficient defrosting or antifogging, with the large windows we need as much ac as possible.
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Old 10-21-2015, 09:18 PM   #14
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Chris..... Since no one seems to be answering this, I am thinking that maybe the best idea would be something simple like the 570-215 valve, pictured here.

Click image for larger version

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This could be controlled easily by a cable pull on the dashboard. The valve wouldn't have to come from this supplier, since this is a pretty universal style of valve, and a search on Amazon or eBay for "heater valve" will turn up many for $20 or so, and likewise NAPA would stock valves of this type. I have fitted these myself in classic car applications, and they are as simple as could be, available in metal or plastic, and shut off completely. A generic choke cable from a parts house also adapts itself to these, and you just have to crimp a loop at the end in order to hold the actuating peg.
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