Another AC thread...
Thread Starter
Newbie - Just Registered
Joined: Sep 2018
Posts: 8
Another AC thread...
So...first post, but have been a lurker for quite a while. I have an ‘08 maxima that won’t engage the AC compressor.
Things I have already done:
1) IDPM self diagnostic (checks the ac relay 5 times) - engages as should
2) new expansion valve and filter/dryer, and pressure switch
3) charge is correct, roughly 45/175 when compressor is running, 85ish when equalized.
4) I can jumper the compressor and it cools as it should - blows cold
5) ran climate control self diagnostic, all temp sensors show more or less the right temps. Mixer and doors work as well.
If I let the car sit overnight and start it, the compressor will run for a minute or so, and then kick off. Once it kicks off, it will not kick back on. Even if I disconnect the battery and try again. This makes me think something is up with the pressure switch, but I have disassembled and checked the evaporator and condenser with an air hose and they both flow freely. The Freon also equalizes quickly after the compressor kicks off so I don’t think there is a major restriction in the system.
Any ideas??
Things I have already done:
1) IDPM self diagnostic (checks the ac relay 5 times) - engages as should
2) new expansion valve and filter/dryer, and pressure switch
3) charge is correct, roughly 45/175 when compressor is running, 85ish when equalized.
4) I can jumper the compressor and it cools as it should - blows cold
5) ran climate control self diagnostic, all temp sensors show more or less the right temps. Mixer and doors work as well.
If I let the car sit overnight and start it, the compressor will run for a minute or so, and then kick off. Once it kicks off, it will not kick back on. Even if I disconnect the battery and try again. This makes me think something is up with the pressure switch, but I have disassembled and checked the evaporator and condenser with an air hose and they both flow freely. The Freon also equalizes quickly after the compressor kicks off so I don’t think there is a major restriction in the system.
Any ideas??
Sound like you have way too much freon in the system. Did everything work well before you replaced all the parts?
I would not be forcing the compressor to kick in anymore unless you verify that the level of freon is correct. Did you hook up actual gauges to the car or just filled with a can and a hose after all the repairs?
I would not be forcing the compressor to kick in anymore unless you verify that the level of freon is correct. Did you hook up actual gauges to the car or just filled with a can and a hose after all the repairs?
Thread Starter
Newbie - Just Registered
Joined: Sep 2018
Posts: 8
I added based upon equalized pressure that this car has run at in the past, I don’t have a proper scale for measuring out in lbs, but based on what I remember from the number of cans it took it was about right for the sticker weight. I didn’t check temperatures with a thermometer but did use a Mollier diagram for 134a to be sure I was in the ballpark. I also referenced it to check what the vent temp should be based on lowside high side differential with the internal sensors that you can check with the onboard diagnostic. I may be able to borrow a thermal camera and check superheat and temps for overall performance.
I vacuum with a refrigerant pump and let it pump for around 2 hours, till it was steady state at around 28.5” Hg. I dont have a micron guage but that should be a good enough vacuum for the system. It held that vacuum for another 3 or 4 hours.
The system is leak tight - the equalized pressure has been in the range I’d expect for a few months at this point.
I also replaced the dryer, so whatever moisture didn’t boil off in the 6 hours it was under vacuum should be within the capacity of the desiccant.
All of these (including oil levels etc) are important for long term system performance, but my issue is what’s stopping the compressor from cycling, even when the indicated pressures at the taps are within the range that should turn it on.
I am am leaning toward a blockage in the condenser that is letting the compressor pump the discharge up to the off set point of the pressure switch without allowing it to equalize/leak down. The compressor discharge has a check valve, and if the blockage is between the high side pressure tap and the condenser I wouldn’t see anything but Backpressure from the low side. The Txv should be wide open at this point. I have found a manual that lists the voltage output for the pressure switch. Since it’s actually a piezo sensor it will output 0-5v over the span of the instrument. I haven’t checked it yet since it has cooled off enough outside hat it’s not an immediate problem, but that’s my next planned step of troubleshooting unless anyone else knows of any compressor or system interlocks that i can test for.
also, I have not notice any corrosion issues, although this could be a bad ground I guess??
I vacuum with a refrigerant pump and let it pump for around 2 hours, till it was steady state at around 28.5” Hg. I dont have a micron guage but that should be a good enough vacuum for the system. It held that vacuum for another 3 or 4 hours.
The system is leak tight - the equalized pressure has been in the range I’d expect for a few months at this point.
I also replaced the dryer, so whatever moisture didn’t boil off in the 6 hours it was under vacuum should be within the capacity of the desiccant.
All of these (including oil levels etc) are important for long term system performance, but my issue is what’s stopping the compressor from cycling, even when the indicated pressures at the taps are within the range that should turn it on.
I am am leaning toward a blockage in the condenser that is letting the compressor pump the discharge up to the off set point of the pressure switch without allowing it to equalize/leak down. The compressor discharge has a check valve, and if the blockage is between the high side pressure tap and the condenser I wouldn’t see anything but Backpressure from the low side. The Txv should be wide open at this point. I have found a manual that lists the voltage output for the pressure switch. Since it’s actually a piezo sensor it will output 0-5v over the span of the instrument. I haven’t checked it yet since it has cooled off enough outside hat it’s not an immediate problem, but that’s my next planned step of troubleshooting unless anyone else knows of any compressor or system interlocks that i can test for.
also, I have not notice any corrosion issues, although this could be a bad ground I guess??
Newbie - Just Registered
Joined: Mar 2020
Posts: 4
I added based upon equalized pressure that this car has run at in the past, I don’t have a proper scale for measuring out in lbs, but based on what I remember from the number of cans it took it was about right for the sticker weight. I didn’t check temperatures with a thermometer but did use a Mollier diagram for 134a to be sure I was in the ballpark. I also referenced it to check what the vent temp should be based on lowside high side differential with the internal sensors that you can check with the onboard diagnostic. I may be able to borrow a thermal camera and check superheat and temps for overall performance.
I vacuum with a refrigerant pump and let it pump for around 2 hours, till it was steady state at around 28.5” Hg. I dont have a micron guage but that should be a good enough vacuum for the system. It held that vacuum for another 3 or 4 hours.
The system is leak tight - the equalized pressure has been in the range I’d expect for a few months at this point.
I also replaced the dryer, so whatever moisture didn’t boil off in the 6 hours it was under vacuum should be within the capacity of the desiccant.
All of these (including oil levels etc) are important for long term system performance, but my issue is what’s stopping the compressor from cycling, even when the indicated pressures at the taps are within the range that should turn it on.
I am am leaning toward a blockage in the condenser that is letting the compressor pump the discharge up to the off set point of the pressure switch without allowing it to equalize/leak down. The compressor discharge has a check valve, and if the blockage is between the high side pressure tap and the condenser I wouldn’t see anything but Backpressure from the low side. The Txv should be wide open at this point. I have found a manual that lists the voltage output for the pressure switch. Since it’s actually a piezo sensor it will output 0-5v over the span of the instrument. I haven’t checked it yet since it has cooled off enough outside hat it’s not an immediate problem, but that’s my next planned step of troubleshooting unless anyone else knows of any compressor or system interlocks that i can test for.
also, I have not notice any corrosion issues, although this could be a bad ground I guess??
I vacuum with a refrigerant pump and let it pump for around 2 hours, till it was steady state at around 28.5” Hg. I dont have a micron guage but that should be a good enough vacuum for the system. It held that vacuum for another 3 or 4 hours.
The system is leak tight - the equalized pressure has been in the range I’d expect for a few months at this point.
I also replaced the dryer, so whatever moisture didn’t boil off in the 6 hours it was under vacuum should be within the capacity of the desiccant.
All of these (including oil levels etc) are important for long term system performance, but my issue is what’s stopping the compressor from cycling, even when the indicated pressures at the taps are within the range that should turn it on.
I am am leaning toward a blockage in the condenser that is letting the compressor pump the discharge up to the off set point of the pressure switch without allowing it to equalize/leak down. The compressor discharge has a check valve, and if the blockage is between the high side pressure tap and the condenser I wouldn’t see anything but Backpressure from the low side. The Txv should be wide open at this point. I have found a manual that lists the voltage output for the pressure switch. Since it’s actually a piezo sensor it will output 0-5v over the span of the instrument. I haven’t checked it yet since it has cooled off enough outside hat it’s not an immediate problem, but that’s my next planned step of troubleshooting unless anyone else knows of any compressor or system interlocks that i can test for.
also, I have not notice any corrosion issues, although this could be a bad ground I guess??
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