No A/C HELP I'm Melting!

[My_Jeep]

1069119

Hey,

I have a 95 Grand Cherokee Limited 5.2 V8 & the A/C is blowing hot! It's been at the dealer many times years past under the extended warranty but that's over. Every time they said there's a leak in the system but obviously never fixed it! I wanted to recharge the system my self using one of those kits at auto stores so I bought one & a can of dyed R-134A so I can locate & fix the leak. Now I connected a pressure gauge to the low side of the system (on passenger side next to fire wall correct me if I'm wrong) & the gauge read about 120PSI's with the car off. The crappy instructions said it should be around 20-40 psi's(I think. I don't have the instructions in front of me). Now I started the car and watched the gauge & compressor. Everytime the ac compressor clutch engaged the pressure decreased to about 18 psi's then the clutch disengaged and shout up to 100 psi's. Can someone tell me wtf all this means!

Thanks for any help. It's really appreciated since tomorrow will be around 100 degrees![addsig]

 

[MudderChuck]

1069128

The good news is the pump is turning on and off. Normal systems (late model) have a couple of pressure switches in the system, as a protection against catastrophic failure. The low switch will generally shut the compressor down, when the low pressure is below the freezing point (theroetical)(or close). Take a look at the temp. scale on your low side gauge and see if 18 PSI isn´t at or close to freezing, which means the system is low on freon, or there is a blockage in the high side of the system (normally at the expansion valve at the cooler/evaporator). The high pressure switch, will shut the pump down when the pressure gets to high, from a blockeage (kinked line,plugged expansion valve) or when air is mixed with the freon. Air expands much more than freon and will run the pressures up, way to high in a hurry.
Visually checking the show glass in the high pressure line, usually near the surge tank or shortly after the condensor (front AC radiator) will generally tell you when the freon is low. At start up(after the system has sat idle for awhile) , the glass window will fill, with pretty much colorless freon. A half a window full, is also usually enough. If the glass is full and you can see bubbles passing through, this is an indication the system has air in it ( a few bubbles is ok).
Trouble points, are the condensor (front radiator) if plugged or restricted, will not condense the freon (turn it into a liguid) and the pressures will go to high and shut the system down.
To little freon, when the freon condenses (shrinks/liquifies) the pressure goes down shuting down the system.
Air mixed in with the freon, will cause high pressures.
Water in the freon will often plug the expansion valve with ice (coldest spot in the system). Often when people add freon, they forget to purge the hoses with a little squirt of freon and the normal moisture in the air, in the hoses, is pushed into the system.
When the AC is pumping out hot air, it is often, air in the system or a plugged condensor. The condensor may be plugged inside the fins, not just on the surface, pollen dust and what not build up in there over the years. When washing the condensor out with high pressure water or compressed air, caution should be exercised so the fins are not blown flat (they are really hard to bend upright again).

Hope I helped and didn´t confuse, knowing refrigeration and teaching refrigeration are two different animals.[addsig]

 

[MudderChuck]

1069129

The standing pressure in the system varies with the outside temperature. Usually around 60-80 PSI. But if the outside temp is 100 F like you menjtioned 100 PSI wouldn´t be unheard of.
You can usually only add freon when the pump is running and the pressure is at 18 PSI like you mentioned. If you leave the valve at the freon bottle open, when the compressor is stopped, freon will often flow back into the freon bottle. Many AC techs. will hook the AC pump magnetic clutch up to a hot wire (jumper), when filling, so the pump doesn´t stop unexspectedly. But this can be dangerous, if the high side pressure, gets to high or there is a blockage in the system (something will blow).
Putting the freon can, in a bucket of hot water (don´t get the valve wet) will help with the fill. And keep the pressure in the freon bottle up, in case of an unexspected compressor shut down (to keep the freon from flowing back into the can).
The best way to find a leak, is with the system shut down, soap every joint in the system with a thick mixture of dish soad and water, use a flashlight and look for bubbles. If the leak was an easy one, it would have probvably already be fixed. The hard ones take a lot of time, a systematic approach. Oil stains at a connector are usually a sure sign of a leak, also oil stains on the condensor or the front shaft, on the pump (in back of the clutch/pulley).[addsig]