Thank you for the kind words!

That's quite a complement thank you! Would love to learn a few things from what you saw over 40yrs. I imagine you must have survived some of these systems?

Thank you!

You're welcome!

Thank you Rod! Was a pleasure putting this together and sharing what I've learned. I'm sure I don't have everything right but definitely with to be dangerous 👍

@@thebandit4393 I have a question, too. I have a 73 Nova in which the condenser was replaced last week with a horizontal type after a leak test showed the old condenser leaked. Now when the AC runs a long time the POA valve freezes up. If I turn off the compressor and leave the fan on it unfreezes and AC blows cold again. Seems like moisture in the system if so why? Maybe the expansion valve, receiver/dryer unit, just didn't flush out all of the moisture before charging or anything else? A little history: It was converted to 134a in the past. When the condenser was replaced, he did not replace the dryer/receiver unit. I asked him why and he stated that it was replaced in the past and the system was not open. I guessed he capped the lines from condenser??? The AC runs better then ever but in the past I wasn't observant enough to see if the POA valve was freezing. Thanks

@@rodcleve What do you mean when you say the POA freezes? It's normal for frost/ice to form on the outside, downstream side of the POA valve and the lines going to the compressor. This happens because there is a pressure drop through the POA and the downstream refrigerant temperature gets even colder than the evaporator temperature. If your evaporator is freezing up it's possible the POA valve is not regulating properly. It could be adjusted to a lower pressure than needed, it could be stuck slightly open (due to debris for example), or it could have an internal leak. I would check the evaporator pressure at the POA valve while the system is running with the blower on low speed. This will allow the compressor to pull the evaporator down to the POA set point and you can see what pressure its regulating to.

Thank you! Hope it was helful

If it's prior to VIR, it should be basically the same setup. I highly recommend the model-specific factory service manual - it has a lot of great info on how the system operates and troubleshooting steps. Good luck!

I like that idea and it's easy enough to do. The long sensing lines are unfortunately due to the lack of available replacements with the proper length.

Ceramic coat headers keeps the heat down also [cannot see in vid] . Engine bay fibre glass evap boxes suffer from poor insulation typical GM . I used sticky f/glass insulation with a foil face to cover the box .

I do have ceramic coated headers but a heat barrier like DEI Firewall and Tunnel Shield would be a great addition. The trick is there just isn't much space between the AC suitcase and the engine for that on my car.

Thanks Roddy. I'll keep that in mind. I'll be going through the cables and vacuum control valve in the next few months to get those moving more smoothly

R134a works at its best when system is 98% or greater full

I see no reason to replace the evaporator if it still holds pressure. I would just flush it (as shown in one of my other videos).

I think that's a great idea. I have been thinking about divorcing the AC switch from the rest of these controls like they did in the 80s. I'd also like to divorce the recirculation function.

Thank you! Yes I am a mechanical engineer, but I don't specialize in thermodynamics or HVAC - just learned some of the fundamentals.

I used a bypass style heater valve, Four Seasons 74781 / Everco 5930. This valve normally allows coolant flow to the heater core, but under vacuum it returns the coolant flow back to the waterpump without passing it through the heater core.

The POA valve has a #12 o ring outlet. I used an Original Auto Air aka Classic Auto Air PN G13-407 Shepard's hook which takes it down to #10 barrier hose. Another option I tried that did not fit well was Nostalgic Auto Air PN G135. See post #1565 and #1579 of this thread for info and photos ls1tech.com/forums/conversions-swaps/1329686-70-nova-ly6-th400-6-0vvt.html

One is connected to the evaporator outlet sensing bulb. The other is an equilizing line to measure the evaporator pressure which connects to a port on the POA. Between the evaporator pressure and the outlet temperature, the TXV knows the superheat and can allow more or less refrigerant through to achieve the desired superheat. Some TXVs have internal equilizing so they measure the evaporator pressure at the outlet of the TXV rather than remote.

I can give you a more detailed run down. If you are in Instagram please message me there. I'm @chevyhotrodder. I notched my subframe to fit the Denso compressor down low. It's the OE compressor on most pickups with Gen III and IV LS engines. I used adapters from Docs Blocs (no longer in business but there are other companies that should have them) to get to standard o ring SAE fittings. I used a Vintage Air condenser but honestly it's just a universal parallel flow type and I ended up not using their mounts or hardlines because I didn't like their fitment. The hoses I crimped myself with a borrowed Mastercool crimper. You can buy barrier hose and crimp fittings a bunch of places. The only special fitting is the "Shepard's hook" on the POA valve which goes from the giant #12 outlet to a #10 hose. I will dig for the PN. You also need a new TX valve and to recalibrate your POA I have a couple other videos on flushing the system and recalibrating. I recommend a trinary switch for fan control. I can video chat or call if it helps. Just ping me over Instagram.

@@thebandit4393 Wow, thank you sooooo much! Very nice detail! Yes I watched your other videos on flushing as well as the POA valve adjustment. Very informative! I'll be ready to start working on this in a few weeks so when I get some parts pulled together I'll ping you on Instagram. I think I have to replace the dryer, condenser and get the compressor of course. Once I have those in hand I'll contact you. I think the most difficulty I'll have will be making up the hoses. Thank you so much!!!

@@stevesgarage7644 No problem. Yes you'll need all those things. You'll also need some PAG oil. I used the truck application amount - hard to say what's needed exactly. Make sure you also flush the POA (I did it off the car into a bucket). I had a friend charge it and he estimated the needed amount watching the sight glass and pressures. I hope you have an adjustable POA - some are fixed. The only problem I have with my system is the vacuum control valve is finicky. Sometimes I get recirc when I expect it and sometimes not. I suspect the control valve needs to be replaced but I don't know if any are available aftermarket, so I may try rebuilding when I take it out next. I saw your video on fixing the control levers. It also helps to relube all the cables and the pivots for the duct flaps. The system works really well if everything is in repair. Good luck and feel free to reach out with and questions.

@@thebandit4393 Thank you! I'm a newbie when it comes to A/C systems but I'm not afraid to dive in. Already checking out a set of gauges and vacuum pump. The system has been open a while so the POA might be junk. Not sure yet.

@@stevesgarage7644 I'm a newbie too. This is the only system I've worked on but I did research it thoroughly and I have a mechanical engineering degree. We learned about refrigeration cycles in school but nothing beats real world experience. For what it's worth my POA was disconnected for 20years and seems to be working just fine. There are some details I didn't mention in the video. For example you'll find a small tube running from the bottom of the evaporator to the POA valve. That's an oil bleed designed to let a small amount of the liquid refrigerant to carry oil to the POA when the system is operating with little circulation (POA closed). There is a small o ring there that also should be replaced but it's not a standard size. I think I was able to order one from classic auto air in Florida.

The heater bypass valve is a Four Seasons 74781 / Everco 5930. It's controlled by the same vacuum control valve on the interior AC controls as the original heater shut off valve so the heater core is bypassed in the vent or max AC positions. I can't recall what application the valve was originally intended for

​@@thebandit4393 Thank you for the info! I'm finally getting around to repairing the A/C in my '72 Ventura II and that would be a great "while I'm there" upgrade. Your Nova looks great, thanks for sharing it with us! 🙂👍

@@michaeldavis3430 Thank you! Feel free to ask any questions you have. You can also find me on Instagram at @chevyhotrodder

I made a small notches in the box to clear the passenger cylinder head and used fiberglass to create a pocket in that area. It is really going to depend on where your engine is mounted exactly and what headers you're using. In my case I'm using Doug's Headers SK100 mounts in the 1/2" setback position along with their headers. There are photos of notching the box in my build thread on Ls1tech.com. Search for LY6/TH400 Nova thread by TheBandit.

Thank you so much. Will definitely read thread.

@@minhdang8165 Happy to help. One other point - your '74 is a valve in receiver aka "VIR" system. It has a POA valve integrated into it that is non adjustable. If you are converting to R134a I think your best option is a VIR eliminator.

I'm gonna order a vir eliminator

That is a safety hi/lol switch which prevents the clutch from engaging if the pressures get too high or if there is a leak and the pressure is too low. I wired it inline with the compressor clutch. It will not cycle the clutch during normal operation. The only time it had any effect was before charging the system when the clutch would not run until some refrigerant was charged into the system.

@@thebandit4393 Thank you kindly.

@@thebandit4393 Is it the same as a binary switch? One wire goes to the compressor clutch and the other to ground or somewhere else?

@@ricardoparra6927 Yes this is referred to as a binary switch. It allows current to flow when the pressure is an an acceptable range. In this case the wire that supplies 12v for the compressor clutch routes from the interior controls to this binary switch, then from this switch to the clutch. Another type of switch is a trinary switch which can be used to control an electric fan.

@@thebandit4393 I truly appreciate the information. I am attempting to do what you've done on a 70 C10 with factory air. I have most components except this switch and how it's wired. Does the other wire go to the switch behind the selector box in the cab, known as the compressor switch operated by a diverter cable?

Yes. I bought the drier from Vintage Air but it's just a universal type. They usually have a port on them for installing a binary or trinary switch. I recommend installing a trinary switch for electric fan control.

I suggest you visit Steve's Nova Site. In the forum for Best of Electrical there is a thread with links to all the available wiring diagrams for each year

Twin turbo and factory AC would be a lot to package. I can't help you there sorry

@@thebandit4393 I believe vintage air has there kit under the dash. It would save space but not money.

@@limitlessautomedia9794 Yes their system is completely under dash. I think if you want factory AC and twin turbos you will have to get very very creative with packaging. It's hard enough to package a twin turbo setup as it is. I'm not going to say it's impossible though. You just might have to route exhaust on the outside of the frame or something similarly out of the box

Pro Car Rally Houndstooth

@@thebandit4393 they hold you in place pretty well at autox?

@@davidtindall6427 The high bolsters are great for autocross. Even with just retractable 3pt belts, I don't have issues sliding side to side (harnesses would really help during hard braking). I did have to modify the Pro Car brackets to lower the seats by about 1" which helped driver position tremendously for me at 6'0" tall. The overall dimensions of the seat are better suited for someone shorter since the lumbar support is a little low for me, the top of the seat is a few inches below my shoulders, and I have to raise the headrest all the way up to position it behind my head. The width of the seat is good for me. I have a 36" waist If you're much larger you might consider the "wide" version of the seat.

I spliced the hi/lo binary switch into the compressor clutch wire so it prevents clutch engagement if the high side pressure is too high or low. I installed mine into the drier but anywhere on the high pressure side of the system will work.

@TheBandit thanks. So, does this switch work as an interrupter and does the input come from the a/c control switch in the cab and does the output go directly to the clutch?

@@ricardoparra6927 Yes it is an interruptor. The wiring for the AC clutch runs from the firewall pass through behind the passenger cylinder head to the ambient freeze switch on the passenger side of the evaporator box then to the compressor clutch. I wired my binary switch between the ambient freeze switch and the compressor clutch.

@@thebandit4393 I appreciate you. My setup is slightly different (70 C10) without the ambient sensor but it may not be necessary. Thank you.

@@ricardoparra6927 The ambient switch is used to prevent AC operation in freezing conditions. The only time it would normally come into play is if you are using the defroster while it's snowy cold outside. I would suggest installing a trinary switch if you want it to also control electric fans in the future. Better to install now rather to have to recharge the system later if you decide to swap one in.