Lx 450, 1996, Air Conditioning

[AnotherSurfer]

I just replaced my Evaporator, Expansion Valve & Dryer.

Took the car to an A/C mechanic to have the system evacuated & charged. The mechanic said the Fan Clutch needed to be replaced. He did no tests but put his hand behind the fan and said, based on the air flow, the Fan Clutch needed replacing. Part ordered along with new belts. He said he did not fully charge the system because the "High Side" pressure went above 300psi when revving the engine.

1) What are the correct High and Low side pressures? Note, I assume the pressures change with the engine RPM and the amount of air across the condenser, is this correct? If it is correct, what is the maximum High side pressure?

2) The A/C is now working, but is operating strangely. There is a strange smell coming through the vents whenever the fan is running at low speeds. Any idea what this smell might be and why it only happens at low fan speed?

3) Also, I have put a thermometer into the air vent and at lower fan speed or when the Auto Temp button is engaged and a lower fan speed is obtained, the Temperature drops. Why does the temperature drop at low fan speed?

4) Since my A/C is working, how do I determine whether or not the system is fully charged?

Thanks in advance ,
AnotherSurfer

 

[mabrodis]

Most of these questions would be answered in a FSM (Factory Service Manual)...I don't have my handy or I'd post the numbers.

Just curious did the a/c dude do the evacuate and let it sit there, to make sure there are not holes in the system? I'm curious because the smell you are smelling could be the freon slowly leaking into the airstream.

The lower temps at slow fan speed would be normal I think, the slower fan speed lets the air cool down more before gets pumped out the vents, it's in contact with the a/c chilled thingy longer.

Did the a/c dude tell you the system was fully charged? I think to measure the charge volume you just measure the low-side pressure, certain PSI means it's full, don't know off the top of my head what that is however.

 

[e9999]

"hand test" looks pretty dubious to me.
Temp varying with speed is a function of sizing of the heat exchanger. The low temp at low speed is not surprising. The heat exchanger is capable of delivering a certain amount of "cold" so the higher the air velocity, the higher its temperature in principle, but then there are some other considerations such as the heat exchanger configuration, size etc.
E