My 63 CDV factory A/C was trash so I replaced every part in the system and converted to R134 . I also installed a STV bypass kit which eliminated the STV all together and converted the system to a cycling system.  I vacumed and charged the system with 36oz of 134. The system is cycling as it should and the pressures are right at 250 high side, cycle off at 25lbs and cycle back on at about 35lbs. It is making plenty of water on the low side hoses and evaporator drain. There is very good air flow through the dash vents .

My problem is this, the best I can do on the vent temps is about 50-55 degrees on a 90 degree day, sitting in the garage or going 65 mph. At that temp I am barely able to keep from sweating. I have checked and double checked the outside air intake and it shows to be operating as it should , shutting off outside air while on recirculate. The techs (where I bought my parts} are great but they were unable to lend any ideas that I had not tried.

I am wondering if anyone has had a similar problem. 

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Comment by Tony and Ginny 429 on August 14, 2018 at 10:48pm
Sounds like you are finally getting the vent temps that are expected from a correctly working Ac system
Congradulation and enjoy the driving comfort you have acheived for yourself
Adds a lot to the joy of the driving experience

Enjoy
Comment by Clovis on August 14, 2018 at 10:36pm

It sounds like you hit the sweet spot for your system. Obviously temps don't lie so my guess would be that it was originally overcharged. Very happy for you and we now have more information that this website can add to it's knowledge base. 

Comment by Michael Forte on August 14, 2018 at 10:35pm

Congrats!   Glad you were able to solve it!  Enjoy it!

Comment by Dana G Cooper on August 14, 2018 at 8:26pm

OK, Here is what happened with my A/C problem. To start, everyone I have discussed this issue with agreed, the system needed  around 48oz of 134. A local A/C guy convinced me that my new condenser was plugged up about 3/4 of the way through. I replaced the condenser and drier a couple of days ago and  began installing freon. The new drier had a sight glass so as I watched the pressures I watched the glass. As I completed the second can (24oz} I noticed my pressures were pretty close, it was cycling good, and the sight glass barely had any bubbles. I checked my vent temps and they went from 38 to 42 as the clutch cycled ! I So I am not certain if my condenser was bad or maybe I was overcharging the system. But it is working great so I am leaving it as it is. Thanks again for everyone who offered suggestions.

Comment by Clovis on August 2, 2018 at 3:24pm

Just to clarify for the uninformed, this does not control the cabin temperature. This just cycles the compressor and stops the evaporator from freezing. The one from old air products has a preset temperature to start and stop the compressor. This one is adjustable to set the optimum temperature that won't freeze the evap to a block of ice. 

Comment by Tony and Ginny 429 on August 2, 2018 at 1:52pm
Clovis

Now this is why i love having you around

The switch offers more temp control that is needed and is --a lot less dollar than a switch that does much less !
How can you beat that !

Great info my friend !!!!!!

Enjoy
Comment by Clovis on August 1, 2018 at 10:42pm

Those have a temperature adjustment dial on them. If it's too cold turn dial to warm it up and if to warm do the opposite. These would solve the fiddling to find the sweet spot with the bulb, wrapping and unwrapping mastic. If your system is setup differently than what I've posted then feel free disregard, have a great day! 

Comment by Clovis on August 1, 2018 at 10:36pm

I purchased the STV update kit from old air products. My system was prematurely cycling off before the system had a chance to get really cold. All it's supposed to do is stop the system from turning the evaporator into a block of ice. After uncovering the sensing bulb almost entirely to get it to cycle less I called old air for some information. They started that it wasn't exact science (as I already figured out) and stated it needed to be moved around and put at the top of the line to find/get the best results. This is why I now recommend these from rockauto.

Comment by Mark S Anderson on August 1, 2018 at 9:06pm

The cycling switch sensor, and expansion valve bulb, should be mounted to the outlet(upper) line of the evaporator, as close as possible to the evaporator case, and should be well insulated to prevent engine heat from interfering with operation.  Make sure nothing comes between the sensor/ bulb and pipe from the evaporator, the contact must be metal to metal.  

If you are still having the same problem, you need to deep-dive the workings of the system, to find out whether you are having a refrigerant problem or an air flow problem.    Maybe you need an HVAC guy to have a look, if you know any, to tell you that which system is at fault.  

You've said that the system reaches 25 psi and cycles off.  Does it still with the new exp valve?

You need to measure the low side pressure of the system while simultaneously measuring the temperature at the outlet (large tube) of the evaporator, near the case, with a contact thermometer.   This will let you know immediately whether the refrigeration part of the system is working as it should.  Search google for "test superheat" for info and videos on how to perform this test, then post the results.   If the low side pressure still goes to 25, the temp coming out should be near 30 degrees before cycling off using r134.  If it reaches that pressure, but the temp never gets that low, you have a refrigeration issue that needs to be addressed.  If it reaches that temp but still blows mid temp in the vents, then you have an air delivery issue.     Do this test, and you won't have to be stumped anymore, you'll know which way to go from here.

Comment by Michael Forte on August 1, 2018 at 8:49pm

I have mine on the outlet tube as close to the evaporator case as possible, basically next to to other capillary tube.  It’s under the sticky tape stuff you see in the picture below. 

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