Whatever happened to that ultra-cold Ford truck?

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tony1963
Posts: 4
Joined: Fri Nov 27, 2020 11:37 am

Whatever happened to that ultra-cold Ford truck?

Postby tony1963 » Fri Nov 27, 2020 11:39 am

I remember someone coming here and saying that their R134a converted Ford truck blew AC at 38 degrees out the vents with the fan on high, both doors open, on a 100 degree day. I don't see how that is possible, but I'd like to know more.
tbirdtbird
Posts: 38
Joined: Sat May 02, 2020 1:48 pm

Re: Whatever happened to that ultra-cold Ford truck?

Postby tbirdtbird » Sat Nov 28, 2020 4:06 pm

Our 1931 Model A Ford with 134 does just that. 134 can work better than ppl think.
Selection of the largest parallel condenser you can fit along with sufficient air movement such as adding an electric fan or better yet installing a shroud on the mechanical fan. If you install a fan recall that long ago the racers determined the best position for the fan blades is for the trailing edge to protrude outward (backward) from the shroud by 1/2"
tony1963
Posts: 4
Joined: Fri Nov 27, 2020 11:37 am

Re: Whatever happened to that ultra-cold Ford truck?

Postby tony1963 » Sun Nov 29, 2020 12:01 pm

Several years ago, I obtained the design specs from the dealer on a 1984 Ford F-series. I ran the calculations on the air flow through the HVAC box, fan speeds, etc.

There was no way at the CFM that results from a blower on HIGH that you can have a 38 degree output when the air temperature coming in is 120 degrees. According to my math, the evaporator temperature would have to be 30 degrees below zero to achieve that temperature output.
tbirdtbird
Posts: 38
Joined: Sat May 02, 2020 1:48 pm

Re: Whatever happened to that ultra-cold Ford truck?

Postby tbirdtbird » Sun Nov 29, 2020 6:13 pm

If the evap is 30 degrees below zero then the vent temp will be 30 degrees below zero, which will freeze the evap into a solid block of ice.
dealers and specs have been wrong before. :mrgreen:
You are welcome to swing by and check my Model A Ford out next summer The aluminum evap helps, too
tony1963
Posts: 4
Joined: Fri Nov 27, 2020 11:37 am

Re: Whatever happened to that ultra-cold Ford truck?

Postby tony1963 » Mon Nov 30, 2020 3:31 am

I know that. My point was that the individual obviously stretched the story. The only way that I could run the calculations to have 38 degree air with 120 degree air comining in at the CFM of the high blower speed was to use 30 degrees below zero as an evap core temperature, which we know can't occur.

Why do people come here and make up stuff?
Al9
Posts: 238
Joined: Tue Mar 10, 2020 3:26 am
Location: Southern Europe

Re: Whatever happened to that ultra-cold Ford truck?

Postby Al9 » Mon Nov 30, 2020 4:49 am

I think these calculations are meant for a 100% fresh air condition.

Such a cold evap could still function properly out in the desert where things get really dry. However, AC has to work nearly about everywhere (except sub-freezing ambient), and that's one reason as for why most block style TXVs are set up to flood the evaporator with liquid refrigerant once the evap fins are about to freeze up (actual evap pressure and refrigerant temp vary depending upon evap design), in an attempt to keep the evap pressure up. This keeps evaporators from getting too cold even before temp probes or compressor control valves do their job. Variable compressors are meant to be fully destroked at these evap temps, fixed displacement piston and vane comps are designed with anti-slugging features, scrolls simply resist slugging by design.

This shows that a factory spec auto AC system is really unable/not meant to achieve such cooling performance levels.

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