What causes AC blockage
Posted: Tue Apr 29, 2025 1:25 pm
Got a Toyota Tacoma 2006 4.0 with what I believe to be a complete ac blockage.
Heres why:
Truck originally had decent AC.
couple months later then only half the front vents would blow cold.
now no change in temperature.
hooked up manifold gauges, close to zero charge left in the sys.
got the system evacuated.
i starting pulling vacuum on low side, the pressure goes down, but the high side does not go into vacuum at all unless the high side valve is opened on the manifold gauge.
the latter causes the vacuum pump to change noise as it sucks the ambient pressure down from the high side.
if I understand correctly, the high side should already have some negative pressure just by vacuuming low side, at least that is what happened on my other Toyota
After one hour of vacuuming the system, pulling vacuum from both high and low side charge ports, we attempt to charge the system from low side port.
low side pressure goes up, high side does not change.
pressure equalizes and we cant get any more refrigerant out of the can, which is still >75% full.
only way to get freon pressure to the high side is by charging to high side port.
so got about 40-60 PSI on both gauges, freon can is open to the low side system and no freon is being sucked in
we attempt to turn the ac on with the switch in the cabin, that doesnt kick the compressor on.
we jump the ac compressor relay, forcing the compressor clutch to activate, high side pressure starts to rise slowly and NO PRESSURE CHANGE from the low side.
this further contributes to my theory that we have a blockage, and it is not possible to charge the system
Plan is to replace condenser assy (includes drier) and expansion valve, clean/replace inline filter, and flush the entire system using an heptane/IPA solvent
After we can get the blockage problem sorted out, recharge with dye and find the leak
but what could have caused such a blockage like this?
I do not want to replace parts just for the blockage to return
I am new to this forum and new to auto ac systems, and am posting to hear thoughts from people with more experience
Heres why:
Truck originally had decent AC.
couple months later then only half the front vents would blow cold.
now no change in temperature.
hooked up manifold gauges, close to zero charge left in the sys.
got the system evacuated.
i starting pulling vacuum on low side, the pressure goes down, but the high side does not go into vacuum at all unless the high side valve is opened on the manifold gauge.
the latter causes the vacuum pump to change noise as it sucks the ambient pressure down from the high side.
if I understand correctly, the high side should already have some negative pressure just by vacuuming low side, at least that is what happened on my other Toyota
After one hour of vacuuming the system, pulling vacuum from both high and low side charge ports, we attempt to charge the system from low side port.
low side pressure goes up, high side does not change.
pressure equalizes and we cant get any more refrigerant out of the can, which is still >75% full.
only way to get freon pressure to the high side is by charging to high side port.
so got about 40-60 PSI on both gauges, freon can is open to the low side system and no freon is being sucked in
we attempt to turn the ac on with the switch in the cabin, that doesnt kick the compressor on.
we jump the ac compressor relay, forcing the compressor clutch to activate, high side pressure starts to rise slowly and NO PRESSURE CHANGE from the low side.
this further contributes to my theory that we have a blockage, and it is not possible to charge the system
Plan is to replace condenser assy (includes drier) and expansion valve, clean/replace inline filter, and flush the entire system using an heptane/IPA solvent
After we can get the blockage problem sorted out, recharge with dye and find the leak
but what could have caused such a blockage like this?
I do not want to replace parts just for the blockage to return
I am new to this forum and new to auto ac systems, and am posting to hear thoughts from people with more experience