Understanding my a/c system-66 426

[Harry L.]

Years ago a garage put a thermostat on the firewall, my compressor is wired to this thermostat which runs a tube that is clamped on the evaporator tube. I also have a rebuilt stv valve with an expansion valve bulb also clamped on the evaporator tube. My system cools good, but I do not know which unit is running my a/c system. I have a heater hose cutoff valve to keep hot water out of the heater core so the is no vacuum control. If I wanted to eliminate the cycling system with the thermostat on the firewall and keep my heater hose cutoff valve, is there a thermostat on my heater box where I would run my green wire from the compressor? Anyone understand what am trying to say? Dutch

[Larry M.]

Re: Understanding my a/c system-66 426

Years ago a garage put a thermostat on the firewall, my compressor is wired to this thermostat which runs a tube that is clamped on the evaporator tube. I also have a rebuilt stv valve with an expansion valve bulb also clamped on the evaporator tube. My system cools good, but I do not know which unit is running my a/c system. I have a heater hose cutoff valve to keep hot water out of the heater core so the is no vacuum control. If I wanted to eliminate the cycling system with the thermostat on the firewall and keep my heater hose cutoff valve, is there a thermostat on my heater box where I would run my green wire from the compressor? Anyone understand what am trying to say? Dutch

Dutch:

A 1966 Chevrolet Service Manual (HVAC Section) and a 1966 AIM (C60 AC Section) will go a long way to explaining how everything works.

The green wire to/from the compressor clutch goes to a simple on/off switch that is mounted under the dash on top of the AC-Heater box passenger side. Excellent pictures of this arrangement on the C2 Forum under AC FAQ (Powershift and 62Jeff main contributors). This switch is then activated by a lever attached to your factory AC ON pull knob. When you pull the AC ON knob out, the cable moves the lever which activates the switch which activates the A6 compressor clutch.

The factory AC system does not cycle the compressor, the compressor runs all the time. The STV valve will/should close down as needed to keep the evaporator core from freezing up during cool outside temperatures and low inside cabin AC load. It should be set for 30 psig for R12 refrigerant. Less for R134a if you are using it (around 26-28 psig for R134a). The Expansion Valve (TXV) evaporator outlet sensing bulb also senses a colder than needed temperature and cuts back on the incoming refrigerant flow into the evaporator, but the TXV valve cannot close off completely as that would deadhead the compressor and cause it issues (high internal heat due to no flow thru the compressor). The TXV bulb is set to provide around 5-10 degrees F of evaporator superheat. It is also evaporator pressure compensated. You don't need to know this, but I added it for clarity.

There is also a vacuum switch on the AC-Heater box (near the AC ON switch) that works the heater inlet coolant valve and moves the heater box inside door to control cabin temperature.

Visit the C2 Forum and check the FAQ Section for Air Conditioning. A lot of pics and good answers to your (and others) AC questions. If in doubt, search under 62 Jeff and Powershift (me) for our comments on this subject over the last ten years. Mike Geary is also a primary contributor……..so you can also search under this name also. 62 Jeff is unfortunately not a current participator anymore……but he was for many years. The www.autoacforum.com is also a great place for information. Go to the TIPS AND FAQ SECTION for a lot of outstanding info on our old AC cars.

Larry

[Harry L.]

Re: Understanding my a/c system-66 426

thanks Larry, there is good information to consume. I have quite the double setup for a thermostat not using the correct thermostat switch on top of the heater box. What is the correct placement of the receiver drier, is the first line into the bottle from the evaporator and the line out to the condenser. I had such a tough time getting those lines in without stripping the aluminum threads, do any receiver-driers have metal threads? I am going to have to redo the connections there, I have a small leak. Is there any trick as to get those lines straight? thanks, Dutch

[Larry M.]

Re: Understanding my a/c system-66 426

thanks Larry, there is good information to consume. I have quite the double setup for a thermostat not using the correct thermostat switch on top of the heater box. What is the correct placement of the receiver drier, is the first line into the bottle from the evaporator and the line out to the condenser. I had such a tough time getting those lines in without stripping the aluminum threads, do any receiver-driers have metal threads? I am going to have to redo the connections there, I have a small leak. Is there any trick as to get those lines straight? thanks, Dutch

[Larry M.]

Re: Understanding my a/c system-66 426

Harry:

I went back to the Corvette Forum C2 AC FAQ Section to try and get you some more info. There was a good thread on the STV valve and on Old Air Products #50-2500P STV Update Kit, which uses a thermostatic switch that may be the same or similar that is on your car. Here is the link:

http://www.corvetteforum.com/forums/c1-and-c2-corvettes/3332839-stv-valve-for-factory-a-c-cars.html

Pay particular attention to the PDF Link in Post #1 that takes you to the Old Air Products #50-2500P installation instructions.

There are MANY MANY more threads in this FAQ Section on Corvette Air Conditioning. You need to take time and go thru them. It appears that almost everyone has had continued problems with the original STV Valve, so they are using this update kit or other things to get around these issues.

Let me know after you view this link and the PDF attachment.

Larry

EDIT: If the Old Air Products STV Update Kit is what you have installed on your car (or something similar) it means that your STV Valve was gutted of many/most of its internal components when the kit was installed. It will not work unless it is completely refurbished and the missing parts replaced. If you view the various comments that were stated in the thread, your retrofit kit may be the best option…….unless you are going for a NCRS PV on your car.

[Harry L.]

Re: Understanding my a/c system-66 426

Are the original rebuilt receiver driers a quality product. Do they have aluminum or steel threads? I know that Jeff Pace sells them. Are there any other vendors rebuilding them? Thanks, Dutch

[Larry M.]

Re: Understanding my a/c system-66 426

Are the original rebuilt receiver driers a quality product. Do they have aluminum or steel threads? I know that Jeff Pace sells them. Are there any other vendors rebuilding them? Thanks, Dutch