75 Monza Factory Air conditioning - Best refurb options?

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75 Monza Factory Air conditioning - Best refurb options?

Postby TTait » Wed Mar 10, 2021 5:31 pm

Hi guys. I'm trying to coax a 75 Monza 262 back to life. Its fairly complete and I'm hopping from system to system as I wait for my parts orders to come in.

The topic today factory air - which seems to be unique in the 75 model year as many things are. The system is physically complete. My car is a 262 V8, auto with Power steering and I presume factory installed air.

At first glance the system is telling me its close to working. On first check it was holding a couple of pounds of residual pressure of presumably R12, so I'm optimistic there wasn't a lot of moisture in the system, etc. I saved whatever gas that was and did a vacuum check on the system, but the system only holds about 10 pounds of vacuum. I'm hoping that the O rings and seals just got tired so the first step is to replace the schrader valves and all the O rings and see what I have. The compressor turns and the clutch pulls in when jumped - good signs. Things appear to be working in the air box, and the fan works on all speeds except full.

The valves went in last nite, they weren't a major source of the leak, O rings are next when the kit comes in. While the system is cracked open though its time to understand what else to deal with.

It appears that on the 75, the dryer uses a desiccant bag? I've never dealt with this before. Is it wise to wise crack this thing open and replace the desiccant bag? there has got to be a huge seal involved with opening the chamber up and I don't see that as available. Can anyone shed any light on what's going on here?

At the same time, I'm used to systems that use an accumulator style receiver/dryer. With an accumulator there is a pressurized bladder that provides constant pressure inside the vessel for the the orifice tube. If I'm just opening up a dryer to replace a desiccant bag, is there no accumulator function? I'm suspicious further because the orifice valve available for Monza online starts with the 76 model year, so I'm wondering if the configuration here is exotic, unsupported, or underwhelming?

At this point I'm generally happy with keeping the car fairly stock. I'm not going full resto-mod on this car, just don't have the funds or time - but if I'm going to enjoy the car in Los Angeles the air needs to work. Is my best path forward to try to bring it back to 1975 spec, or bring it forward to a 75/76 hybrid of some type?

Should I be trying to put in a 1975 style desiccant pack at all?, or is there a different receiver/dryer to go to? What's the full king in that case as I presume I'll need to switch over high pressure and low pressure switches etc.

And thoughts on the orifice valve? I know its going to be tied to above - but if I'm going to crack the system open it makes sense to put in a new orifice valve. The thing is - it doesn't seem to be available. It doesn't appear to be the same as the 76 valve which is readily available. Can I put in a generic VOV instead? Part number?

I'm thinking I'll probably continue to run R12, or eventually run R12. I have a small supply. I may run R12A for a while while I wait to see if the system is stable. My expectations are that even with the best of intentions the AC isn't going to blow me away in this car even running R12, and taking another 5-15% cooling hit converting to R134a would only make matters worse.

Any other tips on the refrigeration side of things appreciated.

As far as the fan not running on high, my manuals should finally arrive in a few days. My fuses look good, and I assume the resistor pack isn't an issue for full speed, so its probably the switch in the dash? Does full speed use a relay? Rock Auto does show a relay available but I assume that would operate all speeds?

If this does turn into a larger job, are there cross reference parts in general to other years or applications that have worked out well?

I've completely rebuilt auto AC systems before from air boxes to every other component and have the equipment to charge and monitor everything, I'm just looking at a 45 year information gap on the parts and options on what I can do with this stuff to get cold to come out.

As always - any help appreciated.

Tom
On my third H Body - 1975 Monza 2+2 4.3L Orange/Black (Current State: Running great - needs the AC finished before summer hits hard)
76 Monza 2+2 L4 (1982-1987)
77 Starfire V6 (1987-1987)
82 Delorean - Universal Raffle Car (2005-2013)
81 Delorean 2009 - Present
17 Chevy Bolt 2017- Sold back to GM for almost a full refund
22 Mustang Mach E on order
TTait
 
Posts: 73
Joined: Sat Feb 20, 2021 1:47 pm


Re: 75 Monza Factory Air conditioning - Best refurb options?

Postby TTait » Wed Mar 10, 2021 9:34 pm

It appears that the car uses a VIR instead of a traditional Accumulator and expansion valve and cycling switch.

I likely need to purchase a modernization it like the one found here:

https://www.originalair.com/vir-elimina ... TNEALw_wcB

I'm sure this is documented on the forum but I'm not finding posts in my search.
On my third H Body - 1975 Monza 2+2 4.3L Orange/Black (Current State: Running great - needs the AC finished before summer hits hard)
76 Monza 2+2 L4 (1982-1987)
77 Starfire V6 (1987-1987)
82 Delorean - Universal Raffle Car (2005-2013)
81 Delorean 2009 - Present
17 Chevy Bolt 2017- Sold back to GM for almost a full refund
22 Mustang Mach E on order
TTait
 
Posts: 73
Joined: Sat Feb 20, 2021 1:47 pm

Re: 75 Monza Factory Air conditioning - Best refurb options?

Postby TTait » Thu Apr 22, 2021 5:48 am

One more post to follow up so solutions are in the record. Got my AC working tonight - thought I'd share what I had to do because its not straightforward.

This applies specifically to the 75, and perhaps more specifically to the V8 because the fit is super tight. There is information here that can help anyone however.

First of all, my post above cites a VIR elimination kit. The kit in general is a good idea, if it was fitted to the applications but its not a good fit, or a particularly good company I'm sorry to say. The "universal kit" listed above doesn't have a chance in hell of fitting in the 75. The connector from the evaporator through the firewall is too close to the fan/plenum and the accumulator can't possibly bolt up to the evaporator once the other plumbing, the expansion valve and suction line, go in between as well.

Instead you start by buying this kit instead as a start:

https://www.originalair.com/vir-elimina ... 7-corvette

(customer service at original air is pretty poor by the way - they aren't malicious, but they don't follow up or offer solutions, or really even own their mistakes. They promise to call you back - I had multiple issues and placed multiple requests for help, no call backs and nobody particularly helpful is willing to get on the phone to help.)

Which is the same price as of spring 2021, but it includes an extra extension tube that goes between the evaporator and accumulator. That tube however is a 90 degree tube, and that puts the accumulator nearly into distributer, certainly blocking the heater hoses which will be tough no matter what.

Instead you need to take this 90 degree extension tube to a shop that will weld aluminum and have it modified , cutting the middle curved section of the tube out so that its a straight extension tube that simply moves the accumulator far enough off the firewall to fit the expansion valve and suction line in.

In my case those lines still interfered with the fan plenum and I needed to cut away a portion of the fiberglass fan plenum and reform it with epoxy and paint it so there was a depression for those tubes to clear and pass through the space that was previously, partially, the fan plenum.

Test fit your accumulator around the other tubes as well as your engine to determine the optimum length for your custom straight extension tube to be crafted out of the previously curved extension tube. I went to a full service radiator shop where they cut out the curved middle of the tube, flared one section of remaining straight tube and slipped it over the other section and then welded them together forming a permanent seal. The resulting straight adapter is about 3.5 inches long.

Before assembly its best to flush your lines and evaporator and condenser - but not the compressor. You can rent a flush kit from the the parts store but you need to buy the fluid. Watch a youtube video and don't make a huge mess. Do not flush the compressor or the VIR or the accumulator, just hoses, the evaporator and condenser. Then, if you have flushed, you will need to add some oil. The more components you flushed, the more oil you will have to add, there are articles to help but you probably want to use Ester or Synthetic Ester oil - not PAG. Ester works with R12, R12 substitutes and R134a. you probably want to add some dye as well. Usually Ester comes with dye, if not you can add it.

When you assemble make sure to get the mating surfaces immaculately clean, install new o rings with perfectly clean hands or gloves, and apply fresh ester oil liberally to the o rings before assembly. Be super careful not to cross thread anything, and use two wrenches whenever loosening or tightening fittings - its very easy to bend a pipe so get a second wrench on the static fitting next to the one you are turning.

Technically you could assemble the system with those parts - but in my case it still wouldn't work. The provided accumulator has two auxiliary ports on it. One gets used for the low pressure cycle switch which comes with the kit, the other will serve as your low pressure port for charging the system. The new problem is in the '75 one of these ports is right up against the fan plenum and useless, so you won't have any way to charge the car with freon when you are done.

If this is the case you must replace the Accumulator in the kit with a similar but reconfigured model - I found the Four Seasons 33204 (Available on Amazon currently for $25) as a perfect solution. This is a similar accumulator but the auxillary ports are in different positions. IF you assemble the system using the Four Seasons Accumulator instead you can use one Aux port for the low pressure cycle switch included with the kit and the second port can be used to connect the low pressure hose for charging.

Once you have flushed the system and reassembled with fresh clean lubricated O rigs at every connection point, tighten all the fittings and vacuum down the system, preferably to about -25psi for at least an hour. If you had the seals open and exposed on your accumulator for more than a few minutes before getting the connections closed or if its even mildly humid when you crack the shipping seals on your new accumulator, then pull that -25psy vacuum for hours to overnight to try to get as much moisture out of the desiccant as possible. Then close the valve on your manifold and make sure you can hold vacuum at least overnight.

The kit can be used with R12, which is still available, or R134a. The 134a won't cool quite as well.

When I am ready to charge, I have the low side blue hose still hooked up to the low pressure port on the accumulator with that valve closed, I hook up the center yellow hose from the manifold to the can of refrigerant with the valve on the can closed, and I then hook up the red hose temporarily to the vacuum pump.

I turn on the pump and pull vacuum first in the red hose, then I open the red valve valve and pull vacuum in the red and yellow hoses, with the valve on the can still closed. Then I open the blue valve and made sure the vacuum in the entire system (including the car is still down at -23 to -26. The can of refrigerant is still closed.

At this point I start the car and put a +12 jumper to the AC clutch and turn the cabin fan on high. Then I close the red valve for the high pressure hose currently hooked up to the vacuum pump, and keep the blue valve open, Then I turn on the valve at the gas bottle hooked up to the yellow hose and the vacuum as well as the suction from the running compressor will immediately start drawing in coolant.

Once the pressures start to go up, keep the red manifold valve closed, but loosen the red hose at the manifold/gauge set slightly. Then hook up the other end of the red hose to the high pressure port. A little of the coolant will begin to leak out of the loose red hose fitting at the manifold you just loosened, but its also blowing the oxygen out of the hose so it can't leak into the closed AC system. After a second or two, tighten the red hose fitting again at the manifold to seal the temporary leak. You can now continue charging the system with virtually no moisture or air in the system at all, even the small
amounts of air and moisture that can be present in the charging lines and manifold.

If you don't want to chance expensive R12 at first you can start by running Johnsons Freeze 12 or R12a which can both mix with R12 in the future and cool better than R134a. If it doesn't leak the 12a you can later switch to R12.

Hope this helps someone someday. Let me know if you have trouble.

Tom
On my third H Body - 1975 Monza 2+2 4.3L Orange/Black (Current State: Running great - needs the AC finished before summer hits hard)
76 Monza 2+2 L4 (1982-1987)
77 Starfire V6 (1987-1987)
82 Delorean - Universal Raffle Car (2005-2013)
81 Delorean 2009 - Present
17 Chevy Bolt 2017- Sold back to GM for almost a full refund
22 Mustang Mach E on order
TTait
 
Posts: 73
Joined: Sat Feb 20, 2021 1:47 pm


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