What's wrong with my a/c

[aikiwaza]

95 dodge neon

the a/c only blows hot air. I checked the a/c system reading the psi off of the thicker diameter tube (which I think is the low pressure end of the a/c, it's the one that DOESN'T run into the radiator) and have a good charge, just boardering on a little too high of a charge. I don't know what else to check. Can anyone give some pointers. I would greatly appreciate it.

[denisond3]

Does the pressure in the low side (the larger tubing) drop when you turn the a.c. on? It normally should. I would expect the pressure to drop from maybe 140 psi (a.c. not on) to 40 psi (a.c. on and compressor spinning). Does the a.c. compressor spin with the a.c. turned on. Dont go by the sound of the fans, although they also need to be running. You have to be able to see the clutch plate on the end of a.c. compressor spinning. Is the drive belt tight enough to really turn the compressor? Some of the 'doors' on the heater/a.c.unit under the dash are controlled by vacuum. If the vacuum supply line comes loose, I dont know that the a.c. would deliver the cool air to the vents.
There are lots of other things it might be too.

[orange_bullet]

there also might be some kind of restriction. maybe a clogged orfice tube

[aikiwaza]

Originally Posted by denisond3

Does the pressure in the low side (the larger tubing) drop when you turn the a.c. on?

yes it drops from 40 psi to about 10 psi but I've tested this only with the a.c. on. If the low pressure side can go up to 140 does that mean that the sitting (or lowest reading) pressure should be at 40 psi... so when I hook a gauge to it, it will fluctuate between 40 and 100 something...?

the compressor is spinning, all the fans seem to be workiing correctly. Drive belt as far as I can tell is tight enough.

Could there be a vacuum problem if the heater works perfectly...? It seems that the air is circulating correctly just not cooling.

[denisond3]

Yes, I think dropping to 10 psi is too low. The high side can go from 100 up to over 240 in normal Ops, and I think the low side should not go much below 40 psi. If it does, I would assume it was either low on refrigerant, or had a blockage at the entrance to the evaporator (-the orifice tube- where the pressure drop is). If it has water in the system, that is where the water is likely to freeze, and prevent enough flow of refrigerant to do any cooling. Its the sort of thing an experienced tech would probably know right away. Im only guessing.
I would think a low side pressure of 10 psi might be low enough to turn the compressor off periodically.

[aikiwaza]

Originally Posted by denisond3

Yes, I think dropping to 10 psi is too low. The high side can go from 100 up to over 240 in normal Ops, and I think the low side should not go much below 40 psi. If it does, I would assume it was either low on refrigerant, or had a blockage at the entrance to the evaporator (-the orifice tube- where the pressure drop is). If it has water in the system, that is where the water is likely to freeze, and prevent enough flow of refrigerant to do any cooling. Its the sort of thing an experienced tech would probably know right away. Im only guessing.
I would think a low side pressure of 10 psi might be low enough to turn the compressor off periodically.

so should I add refridgerent until the gauge reads 40 psi on the low pressure tube when the compressor isn't running (meaning that when the compressor turns on the psi will spike to 80 or 90 psi on the low pressure side)?

[denisond3]

I looked in the Service manual for my 97 Neon. If the ambient air temp is 90°f, the low side pressure should be in the 20-35 psi range when the compressor is running, the high side should be between 290-380 psi range. If its 100°f where you are, the low side pressure would be 25-35 psi, the high side pressure would be 300-400 psi. !!!
But if your refrigerant has leaked out, so has -some- of the lubricant, which for Neons using R-134a is ND8-PAG oil. If all of the refrigerant leaked out when the system was not running, then you might still have a good bit of the 6.75 ounces of lubricating oil. BUT, if the leaking took place while the a.c. was operating, then you might have lost much more of that vital oil. So: You would need to add -some- oil back in. No one will know how much, which is one reason the pros will do a flush and evaucation before doing a recharge. Too much oil can cause hydraulic lock and failure of the compressor. Too little oil will allow the compressor to melt-down.
What the a.c. repairmen charge is actually pretty reasonable. Especially considering they may make Zero profit for more than 6 months of the year.