Compressor Cycles every 30 seconds

[JohnHere]

I am doing the work myself and have access to a manifold and vacuum pump.
I am quite certain the system is not low on refrigerant.
These are the last steps I took after talking to the people on the forum:
1. Vacuumed the system to around 29 in Hg for 30 minutes.
2. Charged the system with r134a cans to the weight listed on the Nissan Label. The cans do not have sealer.
3. Pressures were 30 psi low and 275 psi high.
4. Ambient temperature was 91 degrees.
5. Temperature from center vent was 92 degrees.

Preferably, evacuation could have been for a longer time as already mentioned.

In this instance, the high-side pressure could be interpreted as a little higher than expected at that ambient, while the low-side pressure looks very good. Regardless, you should be getting at least some cooling with those pressures, but "Why not?" is the question.

At 92 degrees, the center-vent temperature suggests that you're getting all ambient air from outside that's somehow bypassing the evaporator, or all-heating, or maybe a combination of both, instead of the expected all-cooling. Double-check for a re-heat condition as previously suggested.

[ACDadforever12]

If reheat was the issue, then the air would be cold until the engine coolant temperature heats up. This is not the case with my car.

I decided to vacuum the system for an hour this time. Then turned the vacuum pump off with the manifold valves closed. After about 15 minutes I did not see an increase in pressure, indicating there is not a substantial leak. I recharged the system once more, by adding the recommended 0.85 kg. This time I saw an extreme low pressure of around 0 psi and a high side pressure of 200 psi. The ambient temperature was 70 degrees at the time of test. Is it possible to damage the expansion valves, or cause a clog? The temperature coming from the center vent was still warm after recharging.

I think I will replace the condenser, drier, and expansion valves. Do you think this will solve the issue?

[Tim]

Nope!

Post pressure at idle, at 1500 RPM, and when the system cycles.

[tbirdtbird]

Per you: If reheat was the issue, then the air would be cold until the engine coolant temperature heats up. This is not the case with my car.

Per JohnHere: At 92 degrees, the center-vent temperature suggests that you're getting all ambient air from outside that's somehow bypassing the evaporator,

To clarify what John meant: you were getting 92° at the vents while the ambient was 91°. That would suggest the air is not seeing the evap at all because of diversion issues, etc. Or maybe the evap is not getting cold at all.
Re-heating is the air gets cold but then is mixed with hot air from the heater core. These are 2 different things.

Please get the pressures, hi and low, as Tim suggested and report back, as requested.
Also, put your hand on the return line from the evap as close to the evap as possible. It should be cold

[JohnHere]

To clarify what John meant: you were getting 92° at the vents while the ambient was 91°. That would suggest the air is not seeing the evap at all because of diversion issues, etc. Or maybe the evap is not getting cold at all.
Re-heating is the air gets cold but then is mixed with hot air from the heater core. These are 2 different things.

That's exactly right. Thanks for elucidating.

[ACDadforever12]

I figured out was was wrong. This is how I found the cause:
- The pathfinder has dual evaporators so underneath the car there are tees that connects both evaporators.
- The suction line from the rear evaporator was cold and the line from the front was ambient temperature.
- Line temperatures indicated the refrigerant was not flowing to the front evaporator. That is why the low side pressure was about half what is should have been.
- I replaced the block expansion valve for the front evaporator, and recharged the system.

This fixed the issue and now the air coming from the front vents is cold again. I was so relieved when it started working again.

Thanks for the help you gave me. The tips were extremely helpful.

[tbirdtbird]

Thanks for letting us know. Good luck with the car!