Another A/C question

[Mike Compton]

ok,
here is the deal. Last summer the air worked perfect. Now I have no air. A friend of mine came over with a can of freon (r134a) and was going to charge the system thinking must be a small leak or something. Well the preasure was really really high. He said that the compressor was kicking in and everything. We sucked all of the freon out of the car, and the compressor kicked off when the preasure got low. then he added just a few oz of freon back in, and it ready as having high preasure again.

Any ideas on this? Does this mean the compressor is not doing its job even though it is kicking in and running? or could this be some other kind of problem? Any ideas?

 

[SHOPWR]

where did you get your manifold gauge set to check pressure ? is your high pressure switch hooked up ? i had a problem like that with a ****** and as it turned out i forgot to hookup the high pressure switch.

 

[Mike Compton]

i could not tell you. It was my friends stuff. I will say this though, All that I saw him do to check preasure was a hose going from the bottle to the connector by the firewall with a gague somewhere along the line.

 

[TYSHO]

i could not tell you. It was my friends stuff. I will say this though, All that I saw him do to check preasure was a hose going from the bottle to the connector by the firewall with a gague somewhere along the line.

That would be the correct outlet, but I can't help you on your problem. I'm experiencing the same on a non-sho car and am curious as to what it can be.

 

[freeze]

what is really really high pressure? on hot days you can hit over 300 psi. also if you added only a few oz of freon after depleating the entire system you would not have enough for the ac to work, usally takes about 2lb of 134.

 

[SHOhhhhMan!]

With the manifold gauge set hooked up to your high-side and low-side service ports, here's what you should be seeing with the car turned off...

Your low side pressure should be the same as the ambient temp., so probably about 70-80psi. If the car has been at operating temp, then expect it to be higher at like 80-100psi. R-134a has a Temperature to Pressure Relationship, or TPR of 1:1 between the temperatures of 20-60*F, and it starts to taper a bit up to like 1.1:1 aright above 60*F. So your low-side should be at roughly whatever the temperature is outside that day.

Now, here's how to calculate what your high-side pressure should be...
You can calculate what it should be by this equation: Ambient temp. X2, plus the relative humidity level. So say the ambient temp is 80*F and humidity is 30%... 80 x 2 = 160... 160 + 30 = 190. Your expected high-side pressure is 190psi.

Now, after you've checked those and VERIFIED that you have a TPR with R-134a in the system, it's time to do a stabilization of the system. Here's how to do that.

With the manifold gauge set still hooked up, start the car, open all the windows/doors, turn the A/C to MAX A/C-Recirculate with your blower on the highest speed. You need to turn the temp to full hot as well to create a heat load on the system. Hold your RPM at about 1500-1700 and have someone watch the gauges. The low-side should cycle between 20-40psi. At 40psi, the compressor will kick on, at 20psi it will turn off. Also watch the high-side, it should fluctuate with the low-side pressure as well, but at a highest psi obviously which is dependednt on the temp and humidity. If the high-side pressure is lower than it should be based on the temp. and humidity, you need to add more refrigerant to the system. If it's way too high, then you're probably having an issue with the condenser being obstructed.

Really though, just go do the basic tests and post back with what you come up with.

You should also check your system for leaks as well; check the service ports for leaks, check all your lines and fittings. You can either use a leak detector, or just feel for oily residue. You should find a < 2 oz. per year leak at the front compressor seal since this is how the compressor stays lubricated., so don't worry if you find a leak there.