97 Camry intermittent problem

[Nedzad1]

97 Camry ac light starts blinking while indoor blower set to any speed except max. Hook up gauges and it appears that once it hits 25 PSI it shuts off fans and clutch and starts blinking. On max blower speed it keeps low side above 25 psi. Compressor replaced last year. New clutch and fan relays also installed. Condenser fans are working fine.

[JohnHere]

Your Camry has a sensor located on the bottom of the compressor that compares the engine tachometer's signal to the RPM signal of the compressor. If they don't match, the light on the A/C button will flash.

A flashing A/C light might further indicate a worn and slipping drive belt, a defective relay, an overcharged or undercharged system, too much oil or the wrong type of oil in the system, a slipping magnetic clutch (weak coil or too wide of an air gap), a defective A/C amplifier, or the sensor itself could be bad or ungrounded.

First guess would be a low charge, especially since the low-side pressure drops below 25 PSI, and then the system shuts off.

Suggest recovering the refrigerant (or having it done) and comparing how much refrigerant comes out to the manufacturer's specification. If there's a substantial difference, then the system has a leak somewhere.

The specs that I have for your car are as follows: 28 ounces net weight of R-134a, and 8.0 fluid ounces of PAG-46. If you have an under-hood decal that lists specs different from the above, then the decal takes precedence.

[Nedzad1]

If I remember correctly this car used to cycle on and off between 25 and 45 psi. It does not do it anymore, once it hits 25 PSI it shuts off ac system. I did try adding some extra refrigerant but it did not make any difference. High side goes above 200 psi and fans will start running really high speed until high pressure drops.

[JohnHere]

If I remember correctly this car used to cycle on and off between 25 and 45 psi. It does not do it anymore, once it hits 25 PSI it shuts off ac system. I did try adding some extra refrigerant but it did not make any difference.

It depends on the heat load. At moderate ambient and cabin temperatures, the compressor should cycle. At higher temperatures, the compressor might not cycle at all. This behavior "assumes" that the system has a correct refrigerant charge.

Your car also has a transducer on the evaporator core that keeps it from getting too cold, freezing the condensate, and blocking airflow. Because the transducer cycles the compressor at ~25 PSI, it sounds like it's doing its job, shutting off the compressor before the evaporator can ice-up. However, the low-side pressure dropping that low also suggests a low refrigerant charge.

One of the first things to look at is to check the charge amount by recovering the refrigerant, weighing it, and comparing the result to the manufacturer's specifications. Any competent shop having a Recover/Recycle/Recharge (RRR) machine for R-134a can do that for you for a nominal fee. Since your car holds a relatively small amount of refrigerant, that amount needs to be exact for the system to operate properly.

High side goes above 200 psi and fans will start running really high speed until high pressure drops.

The fans appear to be working normally, so that's good.

[Nedzad1]

Recovered refrigerant, replaced low pressure switch, accumulator, weight in refrigerant, same problem exist. When in lower blower speed low pressure hits around 23 shuts off and never activate compressor when low side hits 50 psi. It will start blinking in ac switch inside the car.

[JohnHere]

This car has a fixed-displacement compressor, so the low-side pressure shouldn't go as low as 23 PSI if the system is fully charged, is working correctly, and the ambient temperature is 80°F (~27°C) and above. At that low of a pressure, it's bumping into the recently replaced low-pressure cut-off switch and/or the evaporator thermistor, and the compressor is disengaging, as it should. The question is, why is the A/C light blinking and the system not re-engaging?

My second guess is that the system "sees" an RPM discrepancy between the compressor and engine. It's possible that the drive belt and/or clutch are slipping. An oily belt or clutch will do that. It's also possible that the gap between the clutch plates is too wide, preventing the compressor from re-engaging. A new compressor or any new part doesn't always mean that they meet the correct tolerances.

My third guess is that the A/C system has set one or more Diagnostic Trouble Codes (DTC's), preventing the system from re-engaging. Have you scanned it for DTC's (requires a scan tool), or had a shop scan it lately?

... . On max blower speed it keeps low side above 25 psi. ...

The reason why this happens is because at max blower speed, the system is also experiencing a near-maximum heat load. Therefore, the compressor keeps running and doesn't cycle. Once the blower is set to less than maximum speed and the low-side pressure drops below ~25 PSI, the compressor shuts off and won't re-start, along with the accompanying blinking A/C light, indicating a malfunction.

[Nedzad1]

Thank you for your reply. Unfortunately when I did all above and recharge the system it was still having same problem, light was blinking. After driving car next day and almost week after the system has been working fine. It’s cycling as it should and blinking light never came back.
Go figure???