General A/C questions

[rasouth]

I am hoping some of you guys and gals can clarify some A/C questions for me. I know the general function of the a/c system, of pump, condenser, evap, etc.
My questions is/are...
1) How does outside heat affect a/c readings on the gauges? Example- Low side 42, high side 200, outside temp 100, thermometer in a/c duct reads 80.
2) What are the signs of over pressurized system? I got water dripping from bottom of evap, which is normal, hoses do not get wet with condensation. Inside vent temp reads 80 with A/C Max and fan full. No difference at higher RPMs.

 

[8TZX]

If you check a R-134a chart, at 100 F ambient temperature, Low pressure should be 50-55PSI. High should be 315-325 PSI. Appears to be a low charge. What RPM are you running when you check pressures? You should check pressures at approximately 1500 rpms. This helps the air flow through the condenser.

 

[rasouth]

I am usually checking pressure at idle speed, around 900 rpm, but some times I get in and rev it up for a minute just to see what the gauges read.

 

[Jason94sport]

hoses do not get wet with condensation

They should, that's called sweating.
Your ok at idle, I'd give it a little gas once your charging it a few times. Even at 100 your vent temps should not be 80 with AC. You don't have enough charge to cool. Pick up one of the all in one charge cans that has the port connector & the gauge attached. Run half a can in & go from there.
Although if your that low you may have leaking o rings.

 

[Pete Deering]

I am hoping some of you guys and gals can clarify some A/C questions for me. I know the general function of the a/c system, of pump, condenser, evap, etc.
My questions is/are...
1) How does outside heat affect a/c readings on the gauges? Example- Low side 42, high side 200, outside temp 100, thermometer in a/c duct reads 80.
2) What are the signs of over pressurized system? I got water dripping from bottom of evap, which is normal, hoses do not get wet with condensation. Inside vent temp reads 80 with A/C Max and fan full. No difference at higher RPMs.

Response to question 1. First is the compressor cycling on and off or is it running continuous? At outside temp of 100. If your system was at full charge the compressor would be running continuous. The high side pressure should be around 250. The center vent should be around 38 to 50 degrees. If you turn fan speed down to low your center vent temp will be at at a lower temp. And because you are at 900 rpm and fan speed on high 50 degree will be acceptable.
2. the signs of over pressurized system , is continuous running compressor an poor performance, head pressure over 300. The outside temp effect the Freon temp. With the system off the gauge reading should be 100. It like ice is 32 degrees. Water is 33 degrees and above. Explorer have blend door and that why vent temp reads 80. If the high pressure line going into the evaporator is cold something else is the problem. There should be 20 delta T approx. between inlet and outlet.
Spray cold water on the condenser and see if the pressures come down. And the center vent temp also comes down. I have a pipe temp couple that I read the temp on the high pressure line that goes into the evaporator too double check the temperature. The water dripping from bottom evaporator show there is heat transfer. The accumulator should be dripping too.

 

[Pete Deering]

After thinking about your question. Please check your vacuum line to the heater valve in the engine compartment beside the evaporator. If that line is disconnected, you have heat on inside the car with the AC on.

 

[1998Exp]

After thinking about your question. Please check your vacuum line to the heater valve in the engine compartment beside the evaporator. If that line is disconnected, you have heat on inside the car with the AC on.

Even with hot coolant going through you should have cooling as long as the blend door is functional -- just perhaps not as strong. In this case the o/p clearly has a problem with the a/c system itself, because there is no condensation on the hoses.

 

[Pete Deering]

Even with hot coolant going through you should have cooling as long as the blend door is functional -- just perhaps not as strong. In this case the o/p clearly has a problem with the a/c system itself, because there is no condensation on the hoses.

He does have cooling with the blend door is mixing the air. And he does have condensation coming from the evaporator. If the evaporator is cold than the lines are cold.

 

[1998Exp]

He does have cooling with the blend door is mixing the air. And he does have condensation coming from the evaporator. If the evaporator is cold than the lines are cold.

Sorry, I overlooked the fact that water is condensing on the evaporator. Nevertheless, a faulty heater valve is unlikely to be the sole cause of his very poor cooling -- my Crown Vic, with a similar A/C system doesn't have that funky valve at all and did just fine in the 110 degree heat spell here in late June.

 

[Pete Deering]

Sorry, I overlooked the fact that water is condensing on the evaporator. Nevertheless, a faulty heater valve is unlikely to be the sole cause of his very poor cooling -- my Crown Vic, with a similar A/C system doesn't have that funky valve at all and did just fine in the 110 degree heat spell here in late June.

I had the experience, where the vacuum line came off the heater valve and had no cooling because of it. The gauge pressure where in line with what the should be.

 

[rasouth]

I tried recharging it today. My gauges read about 45 on low side, temp was around 100 outside. If I revved the engine the gauge would drop to around 20-25. I hooked up can and began charging, gauge read around 50 on low side but the vent air does not feel much colder. I know my blend door is working because I just replaced it and if I switch to heat I can feel the heat.

 

[Pete Deering]

I tried recharging it today. My gauges read about 45 on low side, temp was around 100 outside. If I revved the engine the gauge would drop to around 20-25. I hooked up can and began charging, gauge read around 50 on low side but the vent air does not feel much colder. I know my blend door is working because I just replaced it and if I switch to heat I can feel the heat.

What is the low side cycling psi? 20 to 45? Need to place a temperature gauge in the center vent to see the temp. Did you check the heater control valve vacuum connection? Is the compressor running continuous? And what is the high side cycling psi?

 

[C420sailor]

When was the last time it blew cold? Was it a sudden change or gradual decline? Was the AC blowing cold since the blend door repair?

 

[RangerNutt]

Yes? We must know!

(Inquiring minds will strip a gear without answers.)

 

[rasouth]

It was blowing cold air on the trip for Fourth of July, all across the Mojave dessert. It just slowly started blowing less cold air. Now it blows slightly cool air. Temp at vents reads 80. Compressor is running continuously, so that would mean I have enough oil in system to maintain 45 psi on a hot day. It is just not cold air.
After fixing blend door everything was blowing cold. Never checked what the temp was coming out of vents at that time.
Anybody know what the signs of over-pressurized system are?

 

[donalds]

Did you consider a plugged up orifice tube

 

[Pete Deering]

It was blowing cold air on the trip for Fourth of July, all across the Mojave dessert. It just slowly started blowing less cold air. Now it blows slightly cool air. Temp at vents reads 80. Compressor is running continuously, so that would mean I have enough oil in system to maintain 45 psi on a hot day. It is just not cold air.
After fixing blend door everything was blowing cold. Never checked what the temp was coming out of vents at that time.
Anybody know what the signs of over-pressurized system are?

The compressor does not cycling. It like going to the top of hill. At the top everything is just right. If you overcharge the vent temp goes up ( getting warmer), the compressor runs continous. And its like going down the other side of the hill. It does not get colder if you overcharge. Our system is design for around two can of r134. 24 oz. It tell you that, label on top of the radiator support. 26 oz max , 7 oz of oil max. How much r134 did you put in?

 

[rasouth]

Keep in mind that the temp outside was around 100 when I hooked up the gauges and started adding the R134a. The gauges were reading around 44-45 psi and I stopped when psi reached around 50. This did not make a difference in vent temp, which was reading at 78.
I am thinking this is not a low charge situation but rather over charged or as donalds suggested maybe a blocked orifice tube.
Too hot here in SoCal to be ripping into the a/c system right now. It may be one of my daily drivers but I don't drive it every day.

 

[Pete Deering]

Keep in mind that the temp outside was around 100 when I hooked up the gauges and started adding the R134a. The gauges were reading around 44-45 psi and I stopped when psi reached around 50. This did not make a difference in vent temp, which was reading at 78.
I am thinking this is not a low charge situation but rather over charged or as donalds suggested maybe a blocked orifice tube.
Too hot here in SoCal to be ripping into the a/c system right now. It may be one of my daily drivers but I don't drive it every day.

Its not a blocked orifice tube. A blocked orifice tube would go into a vacuum psi reading on the low side gauge.

 

[Pete Deering]

Keep in mind that the temp outside was around 100 when I hooked up the gauges and started adding the R134a. The gauges were reading around 44-45 psi and I stopped when psi reached around 50. This did not make a difference in vent temp, which was reading at 78.
I am thinking this is not a low charge situation but rather over charged or as donalds suggested maybe a blocked orifice tube.
Too hot here in SoCal to be ripping into the a/c system right now. It may be one of my daily drivers but I don't drive it every day.

Its not a blocked orifice tube. A blocked orifice tube would go into a vacuum psi reading on the low side gauge.

Do you have a vacuum pump? Or access to one? Did you spray the condenser drop with water? How is the condenser? Is it blocked or are the cooling fins missing? You have a heat transfer problem. If you have a vacuum pump, dump the charge, pull a vacuum and charge it with 24 oz max. It should be cold.