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Date:         Thu, 3 May 2007 16:03:34 -0700
Reply-To:     Keith Hughes <keithahughes@QWEST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Keith Hughes <keithahughes@QWEST.NET>
Subject:      Re: An upgrade for a more efficent A/C system?
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

>Date: Thu, 3 May 2007 09:19:12 -0700 >From: roger sisler <rogersisler2000@YAHOO.COM> >Subject: An upgrade for a more efficent A/C system? > >Hello, > > Vanagon A/C systems need all the help they can get.With either R12 or 134a ,they are marginal. I think the main problems are high heat load inside the vehicle, and small condenser. A second condenser seems to help this situation greatly.That is expensive and difficult to do. Some have done it with very good results.. > > Yes, but that does not address the evaporator sizing, or airflow issues. More on that later...

> It is like driving in the rain in summer.The A/C seems to work much better then. Mine always does.The reason is that the liquid rain conducts heat from the vaporized refrigerant (inside the condenser) much more efficiently. More liquid refrigerant is avaliable for the evaperator, to pick up heat from the interior of the Vanagon. Cooling occurs with the evaperation of refrigerant.Thats why they call it the evaperator. > > Yes, and if the evaporator is undersized, then the volume of liquid refrigerant is moot. In a properly functioning A/C, I don't think you have any appreciable gas leaving the condenser. If you did, you would have no cooling at all. Hot refrigerant will shoot through the expansion valve and the evaporator becomes a condenser. To make use of an additional condenser, you need to upsize the evaporator, and the expansion valve (or adjust it if you have one that's adjustable) to increase the throughput (i.e. refrigerant flow rate) in the system. The expansion valve determines the flow into the evaporator, so the amount of refrigerant that will reach the evaporator is finite.

> Here is a second way that the condenser situation may be improved upon.The Vanagon has a two speed radiator fan. Seldom is the high speed ever used. Only comes on in very hot weather.Sometimes it never ever comes on.. > > If this fan was to be switched seperately from how it is, now ,perhaps the fan could be used to run on high when the A/C is first switch on, or at will. The larger flow of air across the condenser fins is a dramatic way to reduce system pressures, and increase liquid refrigerant > > The problem with this is that the switch you're talking about is designed to save the compressor from high head pressure conditions. As such, it both turns on the high speed fan, *and* disengages the compressor clutch. You could wire around that, but you're asking for trouble. This would undoubtedly help at slow speeds, but at normal driving speeds, the fan is basically irrelevant.

> . Infact the late Vanagon (86-91) has such a high pressure switch to close at 210psi.When this happens,the fan runs on high speed.Why not add a switch on the dash to close this switch at will? Two wires would need to be added at the high pressure switch(easy to do), and be connected to the dash switch.This would bypass the switch when one wanted additional cooling.The existing high pressure switch would still work as installed by VW.. > > The high speed is very noisy, but when it is 100 degrees outside, maybe this noise is not so bad.I hear of 134a systems not working as well as with r-12. Maybe this fix would help this margin. > > It might help, but again, the basic issue is the condenser is designed for R-12. R-134A condensers are larger (for a given evaporator size). If the expansion valve is left as-is during conversion, that is another problem. Should be changed out for proper operation.

In the Westy, one of the biggest problems, IME & IMO, is the airflow short-circuits. That is, too much air is pulled into the return (behind the evaporator) instead of making it to the front of the van. If the air discharge were in front of the front seats, or the return plenum was in the front of the van, the system would work *much* better. Hard to do unfortunately. The passengers in my back seat are always cool, while we in the front swelter. And that's in Phoenix, running R-12. Really need a second evaporator up front, and some additional condenser capacity for it. Me, I just roll the window down...unless the SO is in the van :-)

Keith Hughes '86 Westy Tiico (Marvin)


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