Hello...


Heres' the Vital Stats.. 1977 Dodge Truck with Factory A/C ... All original or original apperaing Parts V-2 Compressor Still runs r-12..


When at a stop light or idle blows comfortable cool air, when moving it warms up.


I am not sure if it warms up due to more air moving over the Condenser core when the truck is runnign down the road or if it's due to the Compressor Running faster due to the engine running at a higher RPM..

I am pretty confident that I can Throw in a new Expansion valve if needed... They are available on Rock Auto and I could Put in a Reciver Dryer if needed also..

I am not sure if it needs a charge as I dont have any r-12 Gauge sets here.. and If needed I have a buddy Who I can Borrow a Vacuum Pump doen from to ro a re-charge if needed..

I hate to break the system open and vent all the r-12 as I do not have a recovery machine..


Any Help is appreciated..


Greg

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http://www.youtube.com/hyperpack

Have you checked to see if the compressor clutch remains engaged when you speed up the engine above idle? Sounds as if you may have improper system pressures -- too high on the high side and/or too low on the low side -- above idle speed. This can be caused by moisture in the system, or a restriction in the system (disintegrated dessicant bag inside the filter-dryer, for example).
That would tend to increase cooling.
You cannot do anything good with this system without gauges. Gauges are an absolute must-have tool to diagnose, repair, and properly charge an A/C system. Trying to do without them will result in wasted money and time, and can also result in system damage and personal injury. Until you have the necessary tools for the job, don't touch it.
Venting the R12 is illegal and foolish. If you feel you must fool with an A/C system you don't have the tools or knowledge to work on safely or correctly, at the very least take it in to an A/C shop to have the R12 evacuated before you start.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

It sounds like the system is low on gas. At a higher RPM you suction pressure is dropping too low and cycling the clutch. At a lower RPM sitting at idle, the system pressure is just high enough to keep the system running, but you evaporator temperature is too low. If it was me I would recover the gas and leak check with nitrogen. I know where you can get some R-12, but it's not cheap.

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R12 is not expensive. Its price peaked quite a number of years ago; demand for it has dropped way off. Remember, the industry changed over completely to R134a in 1994, most of two decades ago. A quick search on eBay will show you that it's not difficult or costly to get R12. However, it cannot be shipped by air and unless the seller (and buyer) are interested in breaking the law it can't be sold to (or bought by) anyone who lacks an s.609 certificate. Moreover, you have to be careful when buying it, because there are a lot of bogus, dangerous, and illegal "drop-in" refrigerants that are not R12 but are sold under misleading names like "FR-12", "OZ-12", "HC-12a", etc.

And the two fundamental points of my earlier post remain: Diagnose, do not guess. And do not touch the system if you do not know what you are doing.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Got me a set of gauges and did took some readings.

According to the Flow Chart in the service manual the pressures on both the Low and High Sides are correct both at idle and at ~2000rpm.

However, there is a greater thatn 6PSI pressure drop between the Low side and the Compressor Inlet which signals a Stuck EPR-2Valve on the Old Chrysler V-2 Compressor design..

Any ideas where I can get such a valve for replacement?

Of course I will neeed to get the R-12 Evacuated from the system before I do this.


Greg

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http://www.youtube.com/hyperpack

Greg, what are the pressures? Give me some numbers. Please.
Let me check, I might have a new valve.

The system might be low on charge. That can cause a "greater the six lb difference". The purpose of the EPR valve is to throttle down and maintain approx 28-30 PSI in the evaporator, to prevent freeze up. Are there any bubbles in the sight glass, on the reciever/drier? That flow chart is assuming a correct refrigerant charge. If you will notice, there is no diagnosis of "low charge". The first step of the setup is "Check refrigerant level".

If you want, give me a call, and I will talk you through trouble shooting.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

My preference when faced with a malfunctioning EPR valve (or, for that matter, a working one on a system I have opened up for some other reason) is to remove it and install a clutch cycling switch instead. Both devices do the same job: regulate the temperature of the evaporator so that it does not go below 32°F. If it were to go below 32°F, ambient humidity that condenses on the cold evaporator would freeze, turning the evaporator into a big chunk of ice. This blocks most/all airflow through the evaporator, and you stop getting cold air out the vents.

As with all fluids, the pressure and temperature of refrigerant are related. You can control either by controlling the other. As pressure drops, temperature drops. As temperature rises, pressure rises.

The EPR (Evaporator Pressure Regulator) valve works by opening and closing in response to pressure in the low-side line that runs from the evaporator outlet on the firewall to the low-side port on the rear of the compressor. When the EPR valve senses low pressure, it moves towards the closed position to reduce refrigerant flow. When it senses high pressure, it moves towards the open position to increase refrigerant flow. It works basically like the throttle valve in your carburetor or the disc valve in your thermostat; it has a range of positions from all the way open to all the way closed. The idea behind the use of an EPR valve (which is just Chrysler's name for a device known generically as an STV, suction throttling valve) was to eliminate the clutch cycling which In a system with the EPR valve, the compressor runs full time whenever the A/C or defog is on, so you don't get perceptible compressor engagement and disengagement -- which I never find annoying, but some marketeers must've thought was objectionable to vehicle owners.

The thing with the EPR system is that it begins to close long before the evaporator freeze-up point is reached, which reduces system performance in high-demand situations (even a crappy, minimal system will keep up with low-demand situations).

A clutch-cycling switch is a thermostatic device that senses the temperature of the evaporator (or the evaporator end of the suction line). It uses a capillary tube filled with a gas that has a specific pressure/temperature curve. One end of the capillary tube is wedged between two rows of fins in the evaporator, pushed into a tunnel into the suction line, or wrapped several turns around the suction line. The other end of the capillary tube ends in a chamber with a flexible metal disc at one end. When the capillary tube gas gets down to a certain temperature, the flexible metal disc contracts, and the spring-loaded switch contacts leaning against this disc trip, opening the circuit to the compressor clutch. The compressor stops pumping refrigerant, but the blower fan continues to run, so air is still cooled and blown into the passenger compartment. This adds heat to the evaporator, which in turn causes the capillary tube to warm up. When the capillary tube gas gets up to a certain temperature, the expansion of the gas pushes the flexible metal disc outward, which pushes the switch contacts together, the compressor clutch circuit is completed, the compressor pumps refrigerant, and the evaporator cools down.

The nice thing about a clutch cycling switch is that it is a binary (on/off) device, so there's no performance reduction curve as the evaporator frost-up point is approached. Also, a CCS doesn't know or care what kind of refrigerant you're using, since its only input is temperature. And with an adjustable CCS, you can tweak the switch's behavior to suit your particular system in your particular car in your particular locale's weather conditions; if you live somewhere very dry, you can nudge the cutout temperature lower to get colder air from the system without danger of frost-up.

Removing the EPR valve and installing a CCS is not difficult or costly. The EPR valve is installed in the compressor. To remove it, you remove the suction fitting (two bolts at rear of compressor). You'll then be staring in at the EPR valve. Sometimes there's a retainer ring; remove it if you find it, then use a small pair of pliers to grasp the valve and pull it out. Use a new gasket when reinstalling the suction fitting.

See here for CCS options readily available in the aftermarket.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dang SSD what DONT you know???

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MRO....

Cheap, Fast, Reliable.... Pick 2...

Actually an EPR/STV/POA valve and variable displacement compressors, all have another function in common, which is actually more important then eliminating compressor on/off "surge", and that is humidity control. With the compressor running full time, you have much better humidity control, especially in moderate temperature situations. The drawback of epr/stv/poa valves is since the compressor is running constantly, there is a fuel mileage penalty. The compressor is still trying to pump a full "load",even though the inlet is throttled. The variable displacement compressor was designed to overcome the drawbacks of the epr/poa/stv valves. The compressor runs full time but varies its displacement based on the heat load that the evaporator "see's". It keeps the evaporator just above freezing (by sensing pressure the same as the valves), and adjusting it's displacement, to adjust the amount of refrigerant, that it pumps. In low load situations, this reduces the Hp requirement of the compressor, and helps with fuel economy, and eliminates the Clutch cycling "yo-yo" effect, and gives great humidity control.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

True enough in theory. In practice I prefer the clutch-cycling system; it's simpler and I prefer the temperature control available with it.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks For the education Dan And Charrlie.. I do understand the CCS Theory.. My 79 Volare has one on it (slant 6's had a c-171 or sanden in '79 while the v-8's still had the RV-2 until 1980) and when the system was charged up with freon it blew sooo cold that I would turn the temp up.... I never minded the Cycling of the clutch...



Charrlie, I do understand your point of the Humidity control.. I think The removal of the EPR valve is in order for me... It's easy enough to retrofit the Truck with a ccs Switch.. and I have witnessed more than one occasion when the RV-2 has had issues with that dang epr valve.


My buddy Brian, who is on the board here and is an HVAC tech has the recovery machine and a vacuum pump for me to borrow to do the job..


Thanks for the Help.

Greg

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http://www.youtube.com/hyperpack

Got the system all working,

Evacuated all the r-12, Pulled the EPR valve and Used a new gasket on the Suction port, checked for leaks Re-charged the system and it is now good at all vehicle speeds.

Without the EPR Valve there is less than a 6 PSI drop between the suction port and the Compressor inlet port which is good.


Will be installing a clutch cycling switch soon.


Thanks for the Help Brian!


Greg

_________________
http://www.youtube.com/hyperpack