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Didnt know I had a Problem

Mackab on Sat August 06, 2005 1:18 PM User is offline

Year: 2000
Make: Ford
Model: Windstar
Engine Size: 3.8
Refrigerant Type: R-134a
Ambient Temp: 83.9
Pressure Low: 35.0
Pressure High: 171.5
Country of Origin: United States

I tested out a Robinair 16800 A/C Diagnostics sytem on what I thought was a known good system. Here were the results:

High 171.5 psi
Low 35.0 psi
Ambient Temp 83.9 F
Humidity 49.3
Floor Temp 83.7 F
Vent Temp 49.9 F
Condensor in 125.5 F
Condensor out 105.7 F
O-Tube in 104.6 F
O-Tube out 100.8 F
Evap in 102.7 F
Evap out 49.5 F
Accum in 46.5 F
Accum out 46.0 F

System displayed: 90.7 percent probability of an evaporator restriction???????

Ran test again a few hours later with same results. Does this sound right? Any help from the gurus would be greatly appreciated.


Chick on Sat August 06, 2005 1:26 PM User is offlineView users profile

You "appear" undercharged. Bring your high side up to around 190 to 200psi at that ambient, while feeling the suction line..Should be very cold....Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

Mackab on Sat August 06, 2005 2:07 PM User is offline

Shouldnt my evap in be colder than my evap out? Im kinda new to this, but the diagnostic prompt called the evap in "the smaller line". I would "guess" that the rerigerant going in would be colder than coming out. Also, how do I bring the high pressure up? Is there a rule of thumb of refrigerant to add to get a certain number of PSI higher? Thanks Chick!!


bohica2xo on Sat August 06, 2005 2:19 PM User is offline

What does this machine use to measure all of those temperatures?

That looks like a parts seller's / service writer's dream machine. "90.7%" odds.... do they make that thing here in Vegas???

If those temperatures are accurate, your condensor airflow is poor, and you are a bit undercharged.

I would question the "O tube out" temperature reading too. Looks like the temp was taken in the wrong spot.....

I can just see the dealership with that machine - ripping the evaporator out of your little windstar, when all it needed was a new fan clutch and a recharge. That machine will pay for itself in a week.

Evaporator restriction? yeah, it is call the expansion device.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Chick on Sat August 06, 2005 2:33 PM User is offlineView users profile

Bring your high side up a little at a time(adding refrigerant) until it's around 2.2 times ambient (electric fan vehicles) and that should correct the machines diagnosis... Hope this helps.

PS. The correct way, of course, is to recover the refrigerant and recharge into the vacuum the correct weight...But doing it by pressures, follow the above..let us know how it works out..

Email: Chick


Freedoms just another word for nothing left to lose

Edited: Sat August 06, 2005 at 2:40 PM by Chick

Mackab on Sun August 07, 2005 6:05 AM User is offline

Tried to add refrigerant and it wouldnt take any. Same pressures as previous. Any ideas?

Chick on Sun August 07, 2005 6:31 AM User is offlineView users profile

With the AC on, it should draw in refrigerant unless you don't have the valve core depresser depressing.. Low side only to charge..Be sure your connection is tight, and raise the idle speed a bit... Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

iceman2555 on Sun August 07, 2005 11:36 PM User is offlineView users profile

As Chick stated the best method to begin is with a system that is known to be fully charged...evac and recharge to specs using the correct recovery and recharge equipment.
When using this test tool, is the 'special' tape being used also? If not this may influence your temp readings.
Also be sure to follow instructions completely when using this equipment.
Try testing with the vehicle at idle...max cool...high blower....doors open. This places the evap in the highest heat load and is much more conducive for temp testing.
The temp at the inlet and outlet of the evap should be the same...or within 3-5 degrees of each other.
The temp drop across the condenser seems a bit low...would expect a bit higher....25-35 degrees.
The temp drop between the OT inlet and outlet should be higher....the temps displayed seem to indicate a leak of liquid refrigerant around the OT. However, this does not seem to a problem...considering the vent temp and pressures.
Start at the correct recharge rates...and then attempt the test once more...using all components of the test equipment and insure that the equipment is being utilized correctly.
Good luck!!!

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Mackab on Mon August 08, 2005 6:40 AM User is offline

I actually took a guesstimate for the orifice tube location so I probably didnt get it right. Can someone tell me where to find it on a 2000 Ford Windstar?

ice-n-tropics on Mon August 08, 2005 10:58 AM User is offline

"shouldn't my evap in be colder than my evap out? Im kinda new to this, but the diagnostic prompt called the evap in "the smaller line". I would "guess" that the refrigerant going in would be colder than coming out."

Your guess doesn't agree with refrigerant thermodynamic properties. If you are interested, let's walk through Thermo 101 to grasp this.

God created Thermo so that we can sweat and cool off as liquid evaporates on our heat exchanger skin surface. We only relatively recently discovered oil and gas as an energy source that enables us to enjoy high efficiency cooling based on the Latent heat exchange properties of refrigerants, in our cars, which can take on or absorb heat in the evaporator and change state from a liquid to a vapor without a pressure change. The first experimental AC car (in 1930) was by Kelvinator for John Hamman in Houston, Texas. The first factory AC car was a 1939 Packard. After all the liquid refrigerant is boiled away or vaporized (due to absorbed heat from the air flowing over and warming the evaporator fins) then the refrigerant gas molecules start to warm up.

Here's the basic concept:
Pressure drop from the evaporator inlet to the outlet is caused by the flow restriction, not the heat absorbed. If all the evaporator is Latent heat exchange, as is normal in a Cycling Clutch Orifice Tube (CCOT) system, there is no Sensible heat exchange (which changes refrigerant temperature increase, like in the superheated outlet refrigerant in an expansion valve type AC system). Sensible heat exchange occurs when there is no change of state, or in this case no refrigerant liquid boiling, only warming of cold refrigerant gas molecules.

Inside a properly charged Cycling Clutch Orifice Tube (CCOT) system the lower pressure saturated refrigerant at the evaporator outlet is colder than the higher pressure saturated refrigerant evaporator inlet. The plate fin (PF) evaporator used with 99 % of CCOT systems has relatively small passageways which restrict flow and cause the refrigerant pressure to decrease. The 1970s PF had only 2 to 5 psi pressure drop but later compact PF heat exchangers have 4 to 8 psi pressure drop or more.

I have explained this thermo dynamic phenomena 3 or 4 times on this forum as one way to achieve an optimum charge in a CCOT AC system. DYIs can actually achieve optimum charge with just your index finger temp sensor, but an objective accurate temp sensor is better. Touch the evaporator inlet and outlet while charging and the outlet will get significantly colder with each increment of charge while (as you near optimum charge) the inlet will basically stabilize temperature. For example:
At evaporator in PSI = 35 psi
evap out PSI = 28 psi
From this web site's saturated R12 temperature table (NEED R134a):
Evap in temp = 36 deg
Evap out temp = 29 deg

With experience you can feel this difference. Try it out to get experience on a few fully charged CCOT systems. Of course, if the system you check is under charged, there could be a superheated Sensible heat exchange zone at the evaporator outlet after all the liquid has boiled away in the preceding Latent heat exchange zone. In this abnormal case, the evaporator outlet will be warmer than the inlet. Maybe this is what caused your first mis conception guess.

Actually for many years, before the limited internal volume multi flow condensers, GM added 1/2 pound of refrigerant above optimum charge on CCOT systems to compensate for hose losses over the first few years. They use less surpluses over optimum charge today due to limited AC system high side storage capacity. In other words, you will have less than the factory OEM charge by using the evaporator in temp verses evap out temp charging method because you didn't allow for hose losses in succeeding years. Also, your head pressures can be a little lower using this optimum procedure verses the OEM charge, especially on older cars when converting from R12 to R134a. Bear in mind that OEMs decide the charging amount at medium high ambient and road speeds.

Actually this same phenomena can occur in the accumulator when the outlet is colder than the inlet. There is usually enough carry over liquid refrigerant or oil containing liquid refrigerant leaving the evap so that there is no sensible heat exchange at the accumulator wall interfaces between the refrigerant and the hot air. Since there is a pressure decrease between inlet and outlet the temperature will also decrease.

Incidentally, the main competitive large scale energy source to keep our decedents enjoying this efficient Latent energy cooling is Wind Turbine energy generation after petroleum is depleted. How will my grand children stay cool when gas is $10+ and rationed for military use against terrorism?

Professor ICE

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

Mackab on Mon August 08, 2005 2:30 PM User is offline

I did have to back out the schrader valve a few turns so my can adapter fitting would push it in. It took a little bit a charge. Here are my new temps. Do they look OK?

High 180.8 psi
Low 38.8 psi
Ambient Temp 80.9 F
Humidity 39.1
Floor Temp 80.7 F
Vent Temp 43.8 F

I still cant find where the O-tube is located. After taking the temps where I thought it might be, the diagnostics machine told me it must be missing. I dont think thats the case, I just cant find it.

brickmason on Mon August 08, 2005 11:40 PM User is offline

The O-tube will be located either at the evaporator inlet or the condenser outlet. Look for 3 dimples in the metal line.

This is the expansion device where the high pressure changes to low pressure.

Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

Mackab on Tue August 09, 2005 1:27 AM User is offline

Do my pressures and temps look OK now?

brickmason on Tue August 09, 2005 1:37 AM User is offline

Looks fine. I wouldnt mess with it anymore.

Just another brick in the wall

Had a little mule I fed him castor oil and every time he jumped the fence he fertilized the soil

chillin out on Thu July 02, 2015 10:07 PM User is offlineView users profile

Mackab, do you still have your Robinair 16800 A/C Diagnostic tool?

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