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Discussion Starter #1
This may not belong in this section but figure most of you visit most all sections for updates.
I just completed my VA install and it seems to have too much head pressure, right around the 375 range:eek: I do have a trinary switch but have not yet wired the fan into it. The ambient temp yesterday was around 104 so I'm guessing the high side should have been around 250 max. I did place an electric fan in front of the condenser (held in position with another helper) and the high side dropped to 325. Suction side was reading 38~42 range and the inside duct temp was 50.

So I drove it home and cycled the A/C at red lights and slow traffic to prevent damage, once on the road and at a steady 65 mph or so the duct temp dropped to 38 and felt good. Engine temp never went over 180. I did stop at the local hot rod supply and purchased a single 16" electric puller fan to install behind the radiator today after work. This fan is rated to pull1900 cfm. I will complete the wiring to the trinary switch as well. Maybe the larger fan will drop the high side too instead of the 14" I initially tried.

What would cause the high pressure - by the way, I started with the recommended 1.8 lbs of freon but recovered it and tried 1.2 lbs then eventually ended up at only 1 lb in the system. All in hopes of lowering the high side reading/ suction side stayed the same.
I am using a Sanden 508 compressor, VA evaporator and their larger natural aluminum in color condenser.

Thanks,
Jason
 

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You're on the right track on reducing the head pressure with airflow, and your 65 mph "test" seems to confirm.

The smaller amount of refrigerant is puzzling to me though.

I assume you are vacuuming the system properly before you charge it?

At 104 degrees outside air temperature, getting to 250 psi may be a bit optimistic.

Maybe someone else can comment.
 

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Discussion Starter #4
You're on the right track on reducing the head pressure with airflow, and your 65 mph "test" seems to confirm.

The smaller amount of refrigerant is puzzling to me though.

I assume you are vacuuming the system properly before you charge it?

At 104 degrees outside air temperature, getting to 250 psi may be a bit optimistic.

Maybe someone else can comment.

Yes, I have the capabilities at work to recover and vacuum the system. I will test it with the new 16" fan to see the outcome of the high side readings. Following VA recommendation my suction side is right were it needs to be at 1500 rpm (steady 6~12), actually I'm at 18. Concerned it is still only 1 lb of freon, little lower than the recommended 1.8 lbs, but is cooling correctly at highway speeds.
 

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My Vintage Air system showed the rated charge at 24 oz of R-134 so I just put in the prescribed amount of refrigerant after completely evacuating the system. My gauge pressures don't show the high head pressure you're experiencing. Could you possibly have some moisture in the system that could be freezing in the expansion valve?
 

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"my suction side is right were it needs to be at 1500 rpm (steady 6~12), actually I'm at 18."

That seems too low to me. You want the low side pressure to be 25-30 psi.

A few years back a friend of mine had one of the first '57 units with the electric servo controls (probably one of the first 2 dozen). He had all sorts of problems with the circuit boards, which was common on the first units. He ended up taking the car from Houston to the VA shop in San Antonio. Spent a couple of days there and they fixed the circuit board problems (they probably learned on his car, which was great for the rest of us). Once all that was working, they vacuumed the system and put in the 1.8 lb charge they recommend. His car would cool great when it was idling (had about 30 psi suction there), but it would drop to 15-18 psi at 1500 rpm. It didn't cool well on the highway coming home, but it did well on a short test drive in SA traffic. He brought it to me, and after looking at the gauges I thought it needed a bit more refrigerant. I put about 6 or 8 more oz. in the system (can't remember now), and it has worked perfectly since (maybe 5 years?).

Somewhat in their defense, but only partially, he had a giant condenser from a late model Caddy on his car. It probably held a lot more refrigerant than the usual condenser that VA sells. The condenser was almost exactly the same core size as the PRC radiator that he had and that many of us use. Probably 25-33% bigger than the condenser PRC sells to go with their radiators, and huge compared to a condenser that's the size of the stock radiator. So that may be part of the discrepancy in the refrigerant volume needed.

Which brings up another point. How big is your condenser? Is it a modern design with improved turbulence in the tubes, or is it a refugee from an R-12 instsallation? The reason I ask that is that when you upgrade to R-134 from R-12, the thing that can be the weakest link is the condenser size and efficiency.

I am convinced that the good performance of my friend's system was the big condenser. That may be what you really need.

One other thing, he had dual 11" fans on his setup too, with a trinary switch.
 

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That seems to be just like my system that I just installed on my '57 Wagon from Vintage Air. I noticed that the compressor was cycling while driving at highway speeds even in 100+ degree Texas heat. I knew that I put the correct amount of refrigerant in the system and the sight glass is clear with the engine on fast idle and 18 lbs. on the low side and about 250 head pressure. Other than electrical problems that I had at first the system seems to work really well other than that cycling thing at highway speeds. I might try adding a few more ounces of refrigerant. I do have their electric fan and trinary switch set-up too. Radiator in the V-8 location with an engine driven flex fan and no overheating problems with a stock radiator. Thanks.
 

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Jim, what is the temperature at the center vent at highway speed. If it's cooling below 32 degrees, the thermostat switch will cause the compressor to cycle. If it's cycleing because of the trinary switch, then head pressure is out of limits, which isn't a good thing.
P.S. ...The thermostat switch could be set too high also. It is adjustabe, but is supposed to be pre-set. You could try bypassing the thermostat switch and see if that keeps it from cycleing. It's the 2 terminal connector on the evaporator unit. I think they are blue wires.
 

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I'll check the temp at the center vent next time I get a chance. I was afraid it was too much head pressure, but I can see that is not the case after I hooked my gauges up and ran the car at fast idle in the heat of the day. The low side pressure is dropping enough that the system is cycling the compressor.

Thankyou!
 

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Jim, you probably already know this, but with normal head pressure and low suction pressure, more refrigerant is needed and will keep you from cycling.

It really doesn't matter if it's the thermostatic switch or not, could even be the low pressure shutoff.
 

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Thanks Rick,

I was surprised to see that low side pressure fall under 20 lbs. with the heat we are having right now, so I will try adding a squirt or two of 134 next time I have a little left over on a job. But like I said, the sight glass is clear as crystal.

Its another issue, but the biggest problem I have had with this unit is where the main harness plugs into the ECU. They have a problem there. I changed the connector 3 times and the ECU 3 times before I finally got a pair of them that liked each other. They probably thought I was the biggest dummy they had ever dealt with, but I could reach in there and push on the harness connector while holding the ECU and the blower would come back on, or the clutch would kick in, depending on which issue I had at the time, but it always came back to that area. I also had a trinary switch that was assembled wrong and that will give you a fit too. Jim
 

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Discussion Starter #12
"my suction side is right were it needs to be at 1500 rpm (steady 6~12), actually I'm at 18."

That seems too low to me. You want the low side pressure to be 25-30 psi.

A few years back a friend of mine had one of the first '57 units with the electric servo controls (probably one of the first 2 dozen). He had all sorts of problems with the circuit boards, which was common on the first units. He ended up taking the car from Houston to the VA shop in San Antonio. Spent a couple of days there and they fixed the circuit board problems (they probably learned on his car, which was great for the rest of us). Once all that was working, they vacuumed the system and put in the 1.8 lb charge they recommend. His car would cool great when it was idling (had about 30 psi suction there), but it would drop to 15-18 psi at 1500 rpm. It didn't cool well on the highway coming home, but it did well on a short test drive in SA traffic. He brought it to me, and after looking at the gauges I thought it needed a bit more refrigerant. I put about 6 or 8 more oz. in the system (can't remember now), and it has worked perfectly since (maybe 5 years?).

Somewhat in their defense, but only partially, he had a giant condenser from a late model Caddy on his car. It probably held a lot more refrigerant than the usual condenser that VA sells. The condenser was almost exactly the same core size as the PRC radiator that he had and that many of us use. Probably 25-33% bigger than the condenser PRC sells to go with their radiators, and huge compared to a condenser that's the size of the stock radiator. So that may be part of the discrepancy in the refrigerant volume needed.

Which brings up another point. How big is your condenser? Is it a modern design with improved turbulence in the tubes, or is it a refugee from an R-12 instsallation? The reason I ask that is that when you upgrade to R-134 from R-12, the thing that can be the weakest link is the condenser size and efficiency.

I am convinced that the good performance of my friend's system was the big condenser. That may be what you really need.

One other thing, he had dual 11" fans on his setup too, with a trinary switch.
With the little knowledge of the system I too was looking for a suction pressure around 38 but according to VA troubleshooting it is not that high at 1500 rpm.
My system is completely new all from VA but not as the kit. I purchased their larger "natural color" condenser for the crossflow radiator 14x25x.83 and I'm running their chrome drier with the Sandan 508 compressor. I did manage to get the electric fan installed but have yet put the gauges back on it to see the differences in the readings. My compressor is not cycling like Jim has mentioned on his. It is just odd with only 1 lb of freon.

Tomorrow will be the test as we head to Vernon, Texas. Fingers will be crossed that it works great....


Air Conditioning Troubleshooting Guide
Article from Vintage Air



The following guide will help the installer determine if a problem exists in the system that would cause a malfunction. If you are experiencing problems in the physical operation of the unit (blower speeds, door operation, etc.) we encourage you to refer to the wiring diagram located in the instruction manual. Using a continuity or light tester you can solve many of the simple problems by tracing connections, and testing them individually. However, if the unit is functioning correctly, but it is not cooling, you can refer to the following guide that will outline the most common problems encountered by installers.



I Test conditions used to determine system operation:

A. Place Temperature probe (thermometer) into center outlet.
B. Connect the gauges or service equipment to the High/Low charging ports.
C. Place Blower fan switch on Medium
D. Close all doors and windows in the vehicle.
E. Place shop fan or heavy-duty squirrel-cage blower directly in front of the condenser
F. Run engine idle up to 1500 RPM.
These test conditions will simulate the effect of driving the vehicle and give the technician the three critical readings that they will need to diagnose any potential problems.

II Acceptable Operating Pressure Ranges for Vintage Air Systems.

A. R134A Type

1. High Side Pressure (160-250 PSI) * Note - general rule of thumb is two times the ambient daytime temperature, plus 15 - 20%.

2) Low Side Pressure (6-12 PSI in a steady state).

3) Center Duct Temperature (36-46 Degrees F).
 

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I just think 6-12 psi is not enough.

I wish somebody else would comment. I wonder if VA Believes that or if it's a typo.

6-12 psi is going to cause ice to form on the air flow side of the evaporator, and that will eventually block airflow.

I was always taught that the suction side should run at a pressure that gives you a temperature in the evaporator around 32 degrees F. Any lower and you have an icing problem (the evaporator is so cold that the humidity forms ice), or it will cycle so much it won't cool because it's not running enough. Any higher and you're not cool, and you have high head pressure because you have too much refrigerant in the system. Look at your gauge set, the temperature is scaled there as well as the pressure. Temperature vs. pressure is a fixed relationship with refrigerant.

Think back to what I said in that earlier post though. That system came alive when I put just a few more ounces of refrigerant in it. It also had the condenser and fan capacity to handle high side presssure/temperature.
 

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I thought that you would be looking for more like 26 to 30# on a hot summer day with a good fan blowing in addition to the car's fan system.

Tom
 

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Hey Rick,

I went for a test drive yesterday in the 57. The ambient temp was 100+. The farther I drove the more the A/C unit would cycle, and it began to get a bit uncomfortable as you cam imagine. So I came back to the shop and hooked up the gauges. I had 250 head pressure and the low side would get down to about 12 lbs., then the system would cycle. That was at fast idle and the condenser fan running. I added a few ounces of charge to it and the head pressure immeadiatly started upward to 350+, but I still had a low side pressure under 15 lbs., still cycling too. By that time it was difficult for me to determine if the head pressure or the low side pressure was causing the system to cycle. So in a nutshell, I can't seem to find a happy medium. My call is that there almost has to be something clogged in the expansion valve, or the exp. valve is faulty. I'm getting about 38 degrees temp at the center duct as long as the system is not on cycle mode.

Jim
 

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I don't know if this has been mentioned, is the dryer connected in the right direction?
 

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Thanks Don,

Yes, the drier is installed correctly.
I called Vintage Air and they said the low side pressure is supposed to be between 8-14 lbs.
They advised me to evacuate and recharge the system since there was no real way to determine how much charge I had since I had been playing with it. So I did just that and evacuated the system while I was gone to lunch, came back and put 24 ounces in it which is 4 shy of their spec, 1.8 lbs. or 28 ozs., but it was the advice of the tech at VA.
In the shop with the cooling fan running and the engine rpm @ 1500, it will cycle when the low side pressure drops below 12 and the head pressure is just over 200. The temp at the center duct is 40, and it only rises to 44 when the system cycles. A road test is next. I will follow up.

I think I had too much freon in the system.....what surprised me was that even when the high side pressure would get to 300+, the low side would still be under 15.

Jim
 
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