On my 48 DeSoto hot rod (Vintage Air), the AC works great for about 1 hour. Then it "looses It's cool". Seems to be still working, fan blowing good, but AC temp increases until almost not cooling. Has been recharged, checked for leaks, none found. Engine temp running at 190F. Suggestions??
Jack

you may want to call vintage air to see if they can help you diagnose this.
have you done a pressure check [high/low sides] when this happens ?

Evaporator freezing up. My 15 Colorado work truck would do that on the run to El Paso, about four hours into the drive, no AC, turn off AC let fan run and melt the ice, AC works.

Never bothered to get it fixed. But usually when you are low on freon the evaporator freezing is a symptom. I know it's been checked, but being a nonstock application you might need a bit more freon in it. What do the pressures and ambient temps look like?

so the heat valve is supposed to be plumbed in at a specific way.
I think it has to be on the output side of the heater core instead of what you would expect the inlet.
It has to use the "drag" of the heater core to help stop the flow.
If it is plumbed in wrong, it allows the hot coolant to push past it.
Eventually it overwhelms the a/c and you get warm/ hot air.

The question is of course has it always done this, or is it a recent thing?

No pressure check done. Good idea, will see if I can contact Vintage Tech.
Thanks,
Jack

Pressures, don't know. Ambient temp Sunday (last failure) 94F.
Jack

Always. Any suggestions? Can you simplify (I'm old and stupid, not necesarrily in that order). Simplier, the better.
Jack

It sounds to me like your evaporator core is freezing up, which is something the system compensates for with a drain (so water condensing on the evaporator core can drain). 1st thing I'd check is to see if the drain is clogged.

If it is not clogged, I would check with the vendor and find out how their system prevents core freeze, they may pass coolant continuously through the heater core and have a hot air bleed somewhere that keeps the evaporator from icing up. There might be a fail in there somewhere.

Hope that helps.

basic a/c diag. if you do not have/system not equipped with evap temp sensor to cut off compressor when system is cold, system will continue to operate thus freezing the "h" valve causing it to freeze over and not cool. next time it happens, shut a/c off for 90-120 seconds and turn back on, if it cools again, "h" valve is freezing over from over work. then it would need a compressor cycling system of some kind.

Yeah, I put a cycling switch in when I did my R134 upgrade and box re-seal. That's the real fix.

I did find a bad crimp in one of the drain hoses, so I replaced the plastic with a rubber hose. Then the other plastic hose came lose and water drained into the floor board. I now have replaced that plastic drain hose with a rubber one. Have not used the AC since.

Yep, and a low refrigerant charge will cause that. Only way to correctly charge a system is by weight, evacuate and recharge by weight.

ok since it has always done it, I still say you put the valve in wrong.
That is assuming you had gauges on it at somepoint and know it has a full charge.

The problem is the actual valve does not have enough stopping power so they have to put it in an odd place.

So
Engine --> heater core --> Valve --> to engine.

The valve has a direction printed on it.

normally you would think you could do
Engine --> valve --> Heater core --> engine

But if you did that, the valve can't hold back the pressure from the engine and hot water will start to flow into the heater core.
It will eventually get too hot for the a/c to overcome and you lose cooling.

Thanks everyone. I checked Vintage Air website, they have a very good online Tech, that was helpful also. I will check to sure upon original install, I did the correct order. Will be going on another long trip on Oct 11th to car show and drags at Dunn NC. I will let you know how/if the AC works OK..
Thanks,
Jack

I'd bet you've got it to me.

Be interested to hear how it performs on your trip. If it drains adequately and still freezes up, I'd put in a clutch cycling switch if it is not already so equipped.

Is this on a flathead or did you swap something more modern in? I ask because I have a 51 Plymouth I want to add AC too, but keep the flat head.

If you suspect the water valve, disconnect it for this one trip and see how it cools. Also, if you suspect the water valve is the problem, feel the hoses on either side of the valve...with the valve closed one side should be cool.

No. It's a 1st Gen, 392 Hemi from 58 Chrysler.

I have the hot water valve close? Is that correct? It's just a "plumbers" valve with handle to turn water on/off manullay under the hood.

If it freezes up with cleared drains, I'd open your hot water valve and the return a bit and see if that prevents the evap from icing up. You'll probably have to mess with it to get enough heat into the air to prevent freeze, but not enough to warm up your chilled air.