Re: How to vent cool air to the rear fan? Econoline-150 Waldoch conversion

I just bought a used 94 Waldoch conversion with a rear heat/ac unit by
>Pro-Air. The rear heat and a/c work just fine. However, when I turn >a/c off and set control to VENT and temp to COOL and turn rear fan ON, >then WARM air comes out of the rear blower. Is that normal? > >I already read the "Van Conversion Manual" here (http://>
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but it does not say anything>about blowing cool air with a/c off. So I wonder if it is "not a>supported feature" ??

If this is a typical "Rear Air" system you have to have the front air on so the AC Compressor is running to have rear air.

Unless they have a positive refrigerant shutoff solenoid valve or a thermal expansion valve (TXV) on the front heater box AC evaporator coil, they can't run the back air only, because the refrigerant will waste a lot of energy trying to cool the front AC coils.

Even with a TXV on the front evap core, you will waste some energy chilling down the front evaporator coil till the TXV senses it's over cold and throttles off the refrigerant flow. But it will work. You just need a separate wire to engage the AC Compressor clutch from the rear air controls.

I am thinking about installing a shutoff valve such as this page, >
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If I do that, is there a>place I can put the valve so that it can shut off both the front and>rear hot water flows at the same time?

Yes - on the heater hose from the engine if you catch it before the Y splitter sending the hot water back to the rear heater.

If you want these to function as emergency heater water cut-offs in case you spring a leak while on the road, you need to put positive shutoff ball valves in both the supply and return lines. Otherwise the system can and will still leak 'backwards' through the return hoses - it's all pressurized.

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Thanks Bruce, I guess I wasn't clear. I don't want to run the a/c, I just want blow non-hot air. For example, today it was 65 degrees and sunny. Sitting in the parking lot the van gets very hot inside. There is no reason to run a/c in those conditions, just turn on the VENT to COOL. However, VENT COOL does not work in the back of the van. If you select VENT (i.e. not a/c and not max a/c), then it doesn't matter what you set the temperature selector to; it ALWAYS blows hot air to the back. Even if nice cool (65 degree outside) air is coming in the front vents, the back vent still have HOT air coming out.

I am coming to the conclusion that this is just a design flaw, a not- supported feature. Basically if you use the rear fan you must either HEAT or A/C. There is no other choice. For one thing, the rear fan does not have any option for fresh air intake, which is a pity.

Apparently in my van, the rear heater coils are always flowing. If the AC is on, the rear unit is BOTH HEATING AND COOLING the air. Not very efficient -- to say the least. Perhaps my vacuum valve is not working. I found a simple solution. In the summer months, I put a clamp on the heater hose (just under the driver side running board) and this prevent hot water from getting to the rear unit. If I get tired of messing with the clamp, I may install a ball valve.

John