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I installed a Vintage A/C package in my 3100. My problem is when I go down the road 40-50 mph, the air gets warm. When I slow down it cools back down. I charge by the sight glass. It gets cold and it is not freezing up. Every thing is fine when Im parked. My temp on the radiator stays the same. My truck basically has always run cool. I have a 292 motor, an electric pull fan that sits high on my radiator. So its not low enough to pull the evaporator coil completely, the condenser sits lower in front of my radiator. I have been doing A/C work nearly 40 years. So, either the charge isnt right or i need a push fan in front of the condenser coil. Also, Im running around 30-40 psi on the low side at idle. Not sure what it should be. Usually most are around 20 psi. And yes, I brought the engine to running temperature before charging. Thoughts anyone?

It sounds like it is freezing up. Set the output temperature a little bit higher for a few trips and see what happens. I know that the Old Air Products unit has an adjustment to prevent that, but I am not sure on tye vintage air.

If the charge is too low, that will happen. I would recommend getting a set of gauges and setting the charge properly. The sight glass method is slightly better than squinting over your thumb at it. Yes, I know Vintage Air recommends it, but it is still wrong.

Could the drive belts be slipping? Some of these 6 cyl installations have everything running on 1 belt on the crankshaft or a narrow belt in a wide pulley.

George

I want as much air flow as possible in front of the condenser coil so I have two electric fans. One (thermostat controlled 16" puller) is for the engine temp and takes its temp reading at the top of the radiator. The other (a 14 inch pusher) is constantly on when the A/C is on and sits in front of the condenser coil. As for your charge, I don't know what the outside temp in MD is, but at ~90 degrees ambient, you probably should have about 30 psi low side and twice 90 plus 50psi for the high side...or about 230 psi. Old Air has the adjustment feature, Vintage Air does not. I assume you sucked all the humidity out of your lines before starting, yes?

sps, I have zero experience with aftermarket a/c systems, I'm curious about the safeties/control on your set-up. Do you know if the system has any pressure switches? specifically a high side pressure switch? The symptoms that you describe are a little strange, I would think that there is adequate airflow across the condenser at 40-50 mph even if you had no fan. I wonder if at that RPM the high side pressure may be too high and tripping a pressure switch. If you find that your system does have a switch then you can experiment by reducing the refrigerant charge until you see bubbles in the sight glass, take it for a ride. It could be overcharged and causing the problem. Do you have any specs on the estimated refrigerant capacity with the components that you have installed?

Like Buck says, my Vintage Air system was overcharged during a 500 mile road trip at 100 degree temps. I had used one of those "can with a gauge" R134 kits that you buy at FLAPS or Walmart to do a last minute A/C tune up before leaving on the trip early one (cooler) morning. Once the day got hot the overpressure switch would kick in, disengaging the A/C clutch for a few seconds. The pressure would drop, the switch would reset, the clutch would engage and the whole process would start over. At its worse, the whole cycle was happening about once every 3-5 seconds. And no cold air into the cab.

Don't tell the EPA, but my "on the road" solution was to set the idle high by pulling the hand throttle knob while the A/C was running. Then I used a small screwdriver to depress the Schrader valve on the high side of the compressor for a half second or so. That let out a little of theR134 and the "cycle time" of the overpressure dropped 2 seconds or so. Two more quick discharges of R134 and the system quit going into overpressure. I drove the rest of the way home in air conditioned comfort.

Moral of the story is "don't use one of those one can, a hose and maybe a gauge" recharge kits".

What is the high side pressure? The ideal situation is when the evaporator develops a thin skim of ice just before the compressor cycles off. As the ice melts, it absorbs quite a lot of BTU's in the process. It sounds like you don't have enough pressure drop across the evaporator as the liquid from the condenser converts itself to gas as the refrigerant makes its way through the evaporator. That refrigerant evaporation is what cools the air passing over the coil. Monitor the temperature drop of the air as ir passes through the evaporator- - - -it should be dropping 15-20 degrees, minimum. Adjusting the refrigerant pressure by tinkering with the charge weight, and running as low an evaporator fan speed as possible to give the air plenty of time for heat exchange will give the best cooling.
Jerry

My Vintage air has a A/C temp switch, it adjusts the compressor cut in and out pressures, so if it freezes up, I adjusts it up just a smidge. Its not as cold but it keeps from freezing up in high humidity. Also mine runs really low side pressure, like 5 - 10 psi when its on max cool and the cab is cold. I don't remember what the high side was. They don't hold much freon, something like 1. 4 lbs, but don't hold me to that number.

OP said he charged the system by observing the sight glass, I really doubt that the metering device is a thermostatic expansion valve but I'm only making that comparison to factory systems, it's been a long time since they used TXV's. If the metering device is an orifice and he charged it to a clear solid liquid sight glass then it's probably overcharged. I would think that Vintage Air would give specs for refrigerant weight based on the application/kit.

TXVs are actually coming back into vogue. Looking on their website, it looks like all of their kits use them.

Vintage Air definitely uses a Thermostatic Expansion Valve.I am currently battling with my Vintage Air. I believe that mine is icing up and cutting off. The compressor makes a lot of racket and it feels like i am dragging a 10,000 pound trailer with flat tires when the A/C compressor is engages.
My low side is 19 psi, while the high side is as high as 275 on a 90 degree humid day.
I thought that it had been over filled with R-134A, but having some of it slowly removed (by a professional of course) it began to cut off from the low pressure switch.
I sure wish that I would have read your post about turning the temperature knob off of all the way to A/C position before I let out that R134A.
Before I messed with it, trying to make it stop cycling and dragging on the engine, I coulda hung meat in the cab. 42 degrees at the vent on a 90+ degree, humid day.

I quickly looked through some of the Vintage air site, didn't see a reference to what type of metering device is used. A TXV or electronic expansion valve (EEV) would certainly be the preferred method over a fixed orifice. If their kits are using TXV's, good on them. One thing I noticed in a troubleshooting guide was the mention of charge weight of 1.8 lbs., I don't know if every application could use the same amount of refrigerant but if the kit spec'd a certain charge then I would go with it. Non-condensables (oxygen, moisture, nitrogen, oils, etc.) will give some of the symptoms that have been described in this thread. A good place to start would be a complete recovery of the existing refrigerant, deep evacuation, weigh in a new charge per spec.

Yes, I pulled a vacume

I'm getting a scale and charging the 1.8oz recommended. and go rom there.

1.8lb, not 1.8oz

Also, make sure you pull a good vacuum for 10-15 min first to get any dissolved gasses out of the oil in the system. Autozone will loan you a vacuum pump and gauge set for a deposite.

Thanks for the feed back. My heat was not off all the way, fixed that. It does have a TXV valve, so the sight glass is useless. I'm charging with gages and a 30lb jug, I do some A/C work. I'm getting a scale and going to charge the 1.8oz recommended. It is an Old Air System. When I wrote this post, I didnt have the high side hooked up. Thought I would do a quick charge. Silly me! I have a 16" puller fan w/shroud from a 98 Buick. Fits on that radiator like it was made for it. I to now think the charge is to high. With the 292, that's a bigger motor than these systems were designed for. so, definitely some modification to make everything fit. I'll be getting back to it Sunday. I'll let all know how it turns out. Thanks again.

sps, I wouldn't spend any money on a scale. With such small weights a scale is kinda' hard to use. 1.8 lbs. is about 28 - 29 oz., if you can find a 16 oz. can of juice and the normal 12 oz. can and dump them both in after a real good evacuation, I think you'll be fine. It'll be close enough to see if that is the answer. I was typing while you added the last post, I guess with the 30 lb. jug of juice you'll need a scale.

I have a vacume pump. thinking about doing a nitrogen flush, that might be over kill though.

Nitogen won't hurt as long as you can do a good evacuation after. Do you have a micron gage to check your vacuum?

It's a refrigerant scale, I'll use it. They don't cost much. Like I said, I have a full jug of 134a. I didn't go out and buy it, I had it sitting around from work. I'm semi retired now due to arthritis so I can't work like I used to. I still do a little A/C work here and there. Sold off a lot of my stuff.

Just the vacuum scale on my low side gage. It pulls to 30. Been doing that for 40 years now.

Well, you might as well use whatever you have then. Evac and weigh in the charge and see what it does. I've been working on the a/c in my Vette, such a pain to get to everything.

My mini Vintage air system had me insert the probe into the case, the probe was part of the 4 knob control system. It makes adjustments pretty easy, the 1.8 charge sounds right. They told me adding extra hose shouldn't effect the charge very much since I added extra low side hose.

When you pull a vacuum for 30 minutes, then do a nitrogen flush, do you need to replace the oil?

There should be no reason to replace the oil if the system had no mechanical failure. If you are going to purge with nitrogen to help expel refrigerant/atmospheric contaminants, you would do that prior to the evacuation. Be careful with the nitrogen, tank pressure is extremely high, you need a regulator on the tank and you don't want to pressurize the ac system beyond its high side pressure rating. Also, don't blow the oil out of the system if you don't plan on a total oil replacement, you will have no idea how much oil is left in there. You don't want to "overfill" with oil because it takes up volume that should be refrigerant.

I'm not going to flush, no need for it. So had some problems that I corrected. The O rings supplied with the fittings were to small. I wasn't holding a vacuum. Larger O rings took care of that. Yes, I used the green ones. I got the heater shut off all the way now. I didn't realize it was on. The valve was open just a little bit. I thought the heat was from the inside of the cab. Now with the A/C off, it blows cool air, not hot any more. That would screw up the charging. Got the scale for about $70. Nice scale to. So on to a weighed charge in a few days. I'm not driving the truck, just sitting in the garage with the gages and a vacuum till I can get to it.

Good to find actual problems that you can remedy, looks like you're on the right track. Hopefully you have specs that give you an accurate charge weight. Keep on keepin' on!

For general reference, I don't think 30 minutes of vacuum is enough. What you are doing is boiling off any water that may be in the system and some of it may be disolved in the PAG oil or should I say emulsified? Anyhow, you have to give it enough time to boil off the water into vapor that can be sucked out of the system.

I just did mine to cure freezing symptoms. I was lazy last summer when I swapped engines and didn't evac the system. On all systems I pump it down for an hour and if the rig can be left overnight I leave the gauges hooked up (disconnect the pump and close the valves) and check it in the morning. Any water boiling off overnight will reduce the vacuum toward zero (as will leaks, but that's another story). This time I found it lost a few microns so I pumped it down again for 30 min and called it good.

If a system is overcharged the compressor will likely be noisy as it's getting some unevaporated liquid on the low side. Enough of that will destroy a compressor.
If you don't know how much refrigerant to use you can figure it out by measuring superheat or subcool (depending on whether it's an orfice tube or TXV). Read up on the subject and you'll find how much of either you should have. A manifold set and a digital thermometer are mandatory. This is how techs doing whole-house, or custom, commercial systems figure it out as there's now way in advance of knowing how much refrigerant to use. Robinaire and others have on-line courses on the subject.