[Stein]

I wanted to thank those who have taken the time to educate me on how to repair this AC unit. The car is worth about $1500, and I couldn't spend $1000 on the AC. I also didn't want to spend $300 on the ac ... which is the minimum I would have spent had I taken it in. The control diagrams were very helpful too.

THis is about the 97 Contour that had a bad clutch gap. I decreased the clutch gap and finally got to where I could check the 134a loading with a gage set .... and something interesting happened.

First: Temperatures:

82 ambient
42 in middle vent w/ blower on high
130 at condenser (bottom of condenser)
95 to 105 in engine depending on where its measured.

First question: Which temperature should I use? I should use the temperature of the 134a at the high side port. Well, which temp is that? The bottom condenser temp (output) or upper condenser temp (input side)? I don't know (didn't think to look) if the high pressure port is on the inlet or outlet to the condenser.

Anyway.

Idle: Low press: 38psi / High pressure 240psi
1200 rpm Low press: 32 psi / High 300 psi
3000 rpm Low press: 28psi / High 325 psi

I thought those high side pressures were high and was concerned. Then I got suprised by the high speed fan kicked on. When the high speed fan kicked on, the high side pressure decreased to ~260 psi. This is more in range with where it should be.

So, when checking with gages, it is also important to have the high side fan on. I guess this is why some people recommend to spray the condenser with water and then check the pressure.

Second question: Could someone who does this explain this procedure and pressures when spraying the condenser with the garden hose?

Last, I've concluded that almost all the oil stays in the system if the 134a is recovered in the static condition. IF the 134a is recovered while running, my guess "rule of thumb" would be that 40% of the oil stays in teh system.

THe unit cools well and doesn't short cycle. AGAIN, MANY THANKS TO THIS FORUM for the help and education to let me repair this.

[royesses]

Congrats on the success-we are proud of you.

You must always charge the system with the amount of refrigerant listed on the label on the vehicle. This is the amount that the refrigeration engineers have determined to be the most efficient in that vehicle.

The gauge readings are for trouble shooting and confirming proper operation, along with vent temperatures. The garden hose can be used to lower the pressures to help push in the charge quicker, besides trouble shooting purposes. I always measure the temp at the middle of the condenser. Others may do it different.

The following link has some graphs from Ford on expected temperatures/pressures. Normally most readings are taken at 1500 rpm.

Ford AC Charts and information

[Skyhawk]

Without getting to deep in the physics....as temperature (ambient) rises so does the expansion of material. In a sealed system, e.g. the A/C system, the expanded materials has to produce more pressure. Cool it down, e.g. the fan draws cooling air over the condenser or water cools the condenser, and the pressure decreases. The pressure flucuates within an acceptable range in the system. The system is "protected" by a low pressure safety switch and a high pressure safety switch as well as a high pressure relief valve. You want the pressure to be within the acceptable range given the fluctuation in temperatures. The Helms manuals, and other resources, will give you graphs and readings (temps and pressures) used to do diagnostic work as well as service the system.