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 Michael Forte on July 25, 2018 at 11:11pm

Dana, just to understand this...you said below that the evaporator outlet is frosting but the evaporator body wasn't cold.  Both the inlet and outlet should be very cold and if so, I can't imagine why the body would not be unless it were some sort of installation issue.

Mark's description of the OAP STV update kit is spot on.  It guts the STV and just uses a temperature controlled switch to cycle the compressor.  I just posted the OAP instructions on my 134a blog post so you can see what's involved.

Comment by Clovis on July 25, 2018 at 11:09pm

I installed the old air products STV update kit. I had to fiddle fuck with the temperature sensor to get it closer to working right. You can basically gut the the STV and make a new gasket for free. Then go to rock auto and find a temperature sensor that cycles the compressor for 10 or so bucks. Get the one with the adjustable temperature dial so that you can find tune it without moving the temperature bulb all over the place. You just adjust the knob for more or less cold.

Comment by Mark S Anderson on July 25, 2018 at 10:20pm

The STV update kit is the same as a bypass kit, only it uses the outer shell of your original STV and a mechanical pressure switch rather than a thermostatic switch.  To install the STV update kit, you gut your existing STV and turn it into a straight pass-thru.

If you have low pressure in your evap and high temp, then there isn't enough liquid getting through your expansion valve, assuming all other things being correct..  Check the superheat going into the STV pipe with a contact thermometer, if it's not within 10 degrees, you need to fix your flow problem (too little refrigerant, plugged component in system, or faulty thermal expansion valve)

Comment by Dana G Cooper on July 25, 2018 at 8:37pm

Just an update, I finally was able to open the a/c case inside the car, and even though my pressures and cycling specs were good, and the evap outlet was frosting between cycles,  the evaporator body was not getting cold. I have ordered the STV 134 update kit from Caddy Daddy, That will likely fix the issue.

Comment by Jimmy Davis on July 25, 2018 at 12:12pm

How long does it take to pull down to 25lbs to cycle off? Symptoms sound like low charge.

Comment by Tony and Ginny 429 on July 25, 2018 at 11:19am
The 134a works at lower internal presuure readings than the R-12
That is why installing the STV is a must to get max cold out out of that system
That will improve gas mileage and system ( compressor ) longevity which are an additional positive to installing the STV

Enjoy
Comment by Dana G Cooper on July 24, 2018 at 10:33pm

I am bewildered, the STV bypass kit that I purchased from Old Air is just a pass through tube with the cycling switch. I questioned the effectiveness of this with an Old Air Tech on Monday and two different techs repeatedly said the bypass tube will work and does work well. I have wondered all along if that could be the problem. That is why I am asking if anyone out there has used the STV eliminator and what were the results?

Comment by Tony and Ginny 429 on July 24, 2018 at 10:04pm
You need the STV kit if you are using the 134a
You will be altering the current suction valve and add the STV kit to it
That will now cause the compressor to cycle on and off and control the pressures in the system that the 134a requires to work properly

Clovis had a few pointers in his tread as to the location of the sensor wire on the suction valve and recommends ---the adjustable STV be used to allow more control of the STV function

That should help get the 134a working in the system as it should at the correct vent temps ( cold )

Enjoy

Enjoy
Comment by Dana G Cooper on July 24, 2018 at 9:46pm

I appreciate all the helpful advice. I pushed as much oil out of the evap as possible, (maybe an ounce), and blocked the oil line going into the STV . That helped a little but it is not there yet ! Has anyone used the STV bypass kit from Old Air ? Just to be clear, the complete change out and not the rebuild kit for the existing STV.

Comment by Michael Forte on July 24, 2018 at 9:34pm

There's a nice diagnostic chart in the shop manual, and the temperature/pressure chart is in there as well.   You should also check to see that the water control valve is off and not sending hot water to your heater core.  That would cause a temperature rise.

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