maroonls1z

Ive been trying to figure out my ac dilemma. Ac request goes through and compressor kicks on. I log pressure sensor and it says 1.2v which i believe is normal but it will not blow cold air. Only does warm and hot. What next?

1 FMF

iTrader: (1)

your pressure sensor... which is the low side pressure sensor, i believe is only a trip switch or and on/off switch. when pressure is below 25-30 psi the switch goes on... or off... telling the computer refrigerant pressure is too low and then the computer turns off the compressor clutch, stopping the compressor in order to protect the compressor. looking at the voltage output of the low pressure ac sensor, via the obd2 port, is not going to do you much good. step 1 of ac trouble shooting is to use a manifold gauge set and look at the high side and low side pressure on the system. step 0 is connect the gauges with engine off and look at system pressure, both high and low side gauges will be equal. with outside air temp above 70°F you should see above 70 psi, if not you are severely low on refrigerant. start engine and turn ac on, the high side gauge should up between 120-200 psi and the low side drop down to 30-50 psi. if high side gauge doesn't go high and low side doesn't go low, possibly bad compressor. if low side goes below 30 psi then compressor kicks off and both high/low gauges equalize until compressor kicks back on, then most likely low on refrigerant. if that's too much for you, call around to a reputable licensed shop that does AC work and ask if they will do a free diagnosis and let you know what's wrong, and go from there.

RockinWs6

What year is the car?

RockinWs6

Not how it works.

maroonls1z

Sorry 2000 camaro, has pressure sensor, no pressure switches

SoFla01SSLookinstok

Well the compressor is turning on so circuitry is ok there.

Is your low side A/C line getting cold?

maroonls1z

Nothing is getting cold, my compressor may have died of the line might be clogged. I hadnt ran the can in like 2 months but it worked fine then

1 FMF

iTrader: (1)

how does it work?

SoFla01SSLookinstok

IMO your write up is pretty accurate.

Before getting to the gauges always perform your visual inspection. We know the compressor is turning on. Checking for temperatures on the A/C lines is great information.

SoFla01SSLookinstok

Man, sounds like the compressor. Hopefully there's no leak. There is still refrigerant in the system as the compressor is still turning on. Good luck man.

maroonls1z

Sucks because i replaced the compressor last year

RockinWs6

Nope not how it works at all, you're not even on the same planet. You guyz are quoting 80's systems. These new systems use a transducer to tell the computer whats going on and the compressor UNLOADS, it never stops..........

What you should do is put gauges on it and turn it on. If the compressor is running you should see low pressure readings in the 30's and high pressure reading in the 200 range and up. Its a place to start. I'll bet the compressor is worn out.

SoFla01SSLookinstok

Uh, ok man. This "new system" is on a 15 year old car.

1 FMF

iTrader: (1)

after looking under the hood to refresh my memory, there is only a high side sensor not a low side sensor.
RockinWs6 was right
I was wrong.
RockinWs6 is very good looking
I am unattractive.
It is a sensor not a switch, and the voltage from it correlates to high side system pressure so that the pcm knows when to turn the radiator fans on either low speed or high speed based on high side system pressure.
however no one here is quoting a 1980's system, which maybe you are thinking of clutch cycling? no one ever mentioned clutch cycling. The AC compressor on the 4th gen f-body is variable displacement, and its an orifice tube type system. the only thing the PCM does is send/remove power to the compressor clutch to engage/disengage it based on a set of conditions. one of the conditions is if the pressures sensor reports to the pcm pressure greater than 410 psi then the pcm will disengage the compressor clutch. the book also states if the sensor sees less than 30 psi it will disengage or not engage the compressor, which will only be valid prior to turning the AC on since the sensor is located on the high side.
In the book it does mention pcm scan tool data list and all it says is a typical value of 1.65 volts for 140 psi.
except for the pressure sensor, what i said above is fundamentally correct and applies to all automotive AC systems using R134a because the operating principle of refrigeration is the same. the compressor needs to pump and you would observe that with a set of mechanical gauges connected to the high and low side service ports and basically know what's what in 5 seconds.


what did you do (or not do) when you replaced the compressor? Did you replace it or did you have someone else do it?

maroonls1z

I replaced it and the accumulator and the orphice tube then took it to someone to flush and vacuum and charge the system... Worked great

1 FMF

iTrader: (1)

my guess is you didn't replace some of the lines that go from hard line to flex and you have a leak. when they evacuated the system it should have held a low vacuum below 1000 micron. and you can look up TSB's from ac compressor manufacturers like 4seasons where they see a high rate of warranty return because systems are not flushed properly and flush residue was left in the system or not all the right parts in the system were replaced- especially if the previous compressor failed.
It's not much different than an engine rebuild- you can do a horrible job but the engine will start and run well... for a short period of time.

RockinWs6

Description of just about every 80's AC systems...............newer systems don't cycle the compressor.

RockinWs6

Should be flushed-cleaned before anything is replaced. Most good shops install a line filter someplace in the system to catch all the trash. You can also buy them online and put one in yourself. If the compressor is coming on what are your pressures?

SoFla01SSLookinstok

We are not on the same planet. When did these "newer systems" start? 1990? 2013??

There are lots of vehicles, that still have low pressure switches, which can cause the compressor clutch to cycle.

Let's say on a transducer system there was some sort of restriction, in the line, that caused the high side pressure to spike or the evaporator to freeze. You're saying it wouldn't cycle?

1 FMF

iTrader: (1)

my 2006 gmc sierra 2500hd with the 8.1L
has a low pressure switch/sensor on the accumulator, and no high pressure switch/sensor. they go all different ways. it really doesn't matter.

and i never said "cycle the compressor". i said turn off, because the sensor detects low pressure because of low refrigerant in the system and shuts off the compressor. after system pressure from the high side equalizes to the low side and satisfies the low pressure sensor (if there is one) and your climate control is still calling for ac then the compressor will kick back on. then you will get a repetitive "cycling" of the compressor... because of low refrigerant in the system... which is not normal operation. I haven't scrutinized every different type of ac system out there and how the car maker chooses to implement **** is up to them.... gm probably screwed up using only a high side sensor and no low side sensor in the f-body which allows the compressor to run with low or no refrigerant in the system.... which also means lack of lubrication at the compressor and is probably why ls1maroonz needs a new compressor. he ran the compressor too long not knowing he was low, starved it of oil and now killed it. that's if he puts a set of gauges on the system and adds refrigerant to see if the compressor still pumps and creates and acceptable high/low side pressure difference.


and if you're installing an inline filter to "catch trash".... you got problems.
ac inline filters are b.s. the only purpose they serve is to make money for whoever sells them.