Engine Size: 3.5
Refrigerant Type: 134a
Ambient Temp: 77
Pressure Low: 25 - 0
Pressure High: ?
Country of Origin: United States
I have a 1999 chrysler 300M (not important really, just age) and my A/C is doing something weird and i hope someone here will have an idea of whats going on.
It works great for about 20 min, then nothing but humid icky air. Tried a recharge bottle of 134a with oil and still the same problem but now i can get pressure readings from the low side.
when it is workin great the low side sits at about 25 psi (engine and compressor running) which seems typical with other owners of 300Ms that i know. however when it is not working there is actually a slight vacuum on the low side. If i leave the car sit over night it works great again in the morning, for ~20 min. when i shut the car off the pressure on the low side slowly increases and levels off at about 55psi which is also normal but a tad low i guess. (no clue what high side is as i dont have a gauge to measure it).
I have not gotten any answers anywhere else i have looked or asked and would really appreciate any help you can give me.
Is there any 'frost' on the high pressure line ? (the long one from the evaporator to the firewall). If so, probably dirt in the system - or the dreaded 'stopleak - causing a restriction to the refrigerant flow or a blockage in the receiver/drier.
If there is no 'frost', then most likely to be excessive moisture in the system. The moisture will freeze and cause a total blockage.
Vic @ Pennine AutoChill
there is no frost that i can see on any lines, the block leading into the cabin is cold but not close to frost levels (assuming that would show some sign as i cannot get to the direct evap tube.)
as far as i know no stop leak/134a has been used in the system at all. i used only 134a with compressor oil.
any way to troubleshoot a bit more to see if it is a moisture blockage?
(i cannot get to the evaporator tube from the interior to the firewall as that is deep inside my dash and a few hours of work to get to it. but i can see it right when it gets out of the passenger area.
the car has been sitting in ~75degree weather for about 2 hours and its still not working, got cold for maybe 10 seconds then back to the musty hot air.
How about posting the high side pressure reading! How much refrigerant is in the vehicle now? How many of these R134a/oil cans have you gone through?
I do not have a gauge for reading the high side, thus no reading.
there should be no leak due to the fact that it works fine the next day so all that is in the system is the stock amount plus one 18 oz can of 134a/oil. i stopped at one because i figured the problem was exactly the same and so chances are more is not the fix.
Would an over charge problem present even when it has been sitting over night?
So a moisture freeze blockage would be moderately consistent event? how would it get in there and suddenly show up like this? (preventative?)
so i take it the first step is take it somewhere and get readings then from there have them evacuate, and refill?
Thanks so much for your help, i really do appreciate it.
Edited: Fri June 19, 2009 at 6:08 PM by ccdoggy
I would guess you have a leak which was causing your original freeze up issue. Now you are overcharged and shutting down do to a high pressure issue related to the moisture and over charged system. There could be many reasons why this system is acting up. Core covered in crap, refrigerant issue, fans not working, pressure switch failing. The first step is to know the refrigerant level and check for leaks. Once you have a know refrigerant level you can start trouble shooting the vehicle.
ok, had the system evacuated and filled with 134a. pressures when working is 25 psi on the low side and 220 on the high side. Worked pretty good... for a while then back to hot and icky. he said chances are its a stuck expansion valve and said he could replace it for about $40 and free 134a refill because he is a good guy. Figured i would replace the drier at the same time because its not that expensive and might be causing the problem.
well I had the system evacuated then I replaced the expansion valve and Dryer. Thankfully everything sealed back up, refilled, and now is working better then ever.
So a vacuum in the low side can mean a bad expansion valve.
thanks for the help.
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