If it's out of refrigerant the compressor won't engage. It'll need to be serviced by a shop that can check vacume and look for leaks. Unfortunately low refrigerant usually equals leak.

 

what other things could cause this?

Being low/empty on refrigerant. If the compressor hasn't run in a long time it might be seized. In that case, bypassing the ambient switch would likely stall the engine so if anyone recommends that I'd think twice. Best thing is to hook up a set of gauges, which will tell you right away whether or not it's ok to do anything that makes the compressor run. If the system is low, you can cause further damage by just buying one of those recharge kits - assuming you can even buy one. Just my opinion, but it's kind of irresponsible to charge systems that are leaking.

 

The temperature sensors do not influence the air conditioning. Perhaps on the digitally controlled new models.
There are a high and low pressure sensor. If either detects outside of range, the compressor will not turn on. You can test for seizure by jumping these switches. Usually it will be the low pressure switch since you are most likely low on refrigerant. If you jump and the compressor tuns on, it is good. DO NOT CONTINUE TO LET IT RUN OR IT WILL NOT BE MUCH LONGER. Just enough to see it engage. There will most likely be no oil in there either.
You can take it to a shop and have them do the pressure and vacuum tests and leak finding / sealing, or if you can, do this yourself. This is recommended. The usual fix for anyone with older cars and less income is a charge can that comes with oil and leak sealer in the can. Some are sold with a gauge to show where the system should be on the fill / low pressure side.
Often the problem of the leak is the o-rings in the lines have deteriorated enough to let the refrigerant escape. The leak sealers fill those cracks. The oil re-lubricates everything. Some have U/V detectable ink to help find any continued leak.
It is often said to not use the leak sealer type recharges. They can clog the system and cause further damage. It is a play at your own risk move especially if you don't know if it was used before. It has been to my experience that cars over 10 years old lose their refrigerant, and can use these without a problem, at least once.
There could be much more catastrophic damage to the lines however, and a leak sealer isn't going to fix that. This is common if the engine or in our case, even just the heads were ever pulled.

 

The temperature sensors do not influence the air conditioning.

They used to have ambient switches. Subject car is 20+ years old, so I was just covering my bases because I've been out of the trade for longer than that.

 

The diagnosis here requires a gauge set and a scan tool. Between those, the problem should be easy to track down. Try an independent shop. Most independent shops charge a flat rate (much lower than regular labor rate) for AC. My last labor rate was $105 an hour. $70 flat charge to look at an AC system. The gauges were hooked up and the computer was scanned for codes (much cheaper rate than the regular $105 hr diagnostic fee). The majority of the time, the system still had (some) pressure in it, but not enough for the electronics to deem it as OK to operate, thus no compressor cycle. If it was low enough, the old stuff got sucked out, pulled a vaccume on it to get moisture out, fresh stuff went it with dye. Customer pays $70 flat rate plus cost of refrigerant per ounce. Usually a $200 job. -Or- it was just "not cold enough"...the pressures were slightly low. It got a squirt of dye, and a 1/4lb shot of refrigerant and send them on their way at $100.

Certainly don't run the AC in it's current state. Unplug the compressor if necessary.

 

The other problem with the recharge cans, if I'm not mistaken, is that the refrigerant does best with as little air and moisture as possible in the system.

 

Correct. AC tech will pull a vacuum on the system. This does two things, removes all air and moisture, and lets the tech know if there is a leak before he jams a can of expensive refrigerant in there.

I am leery to recommend using DIY canned refrigerant. A lot of the cans out there now are counterfeit and filled with butane. Pressurize butane to 300psi and run it anywhere around an exhaust manifold or brake rotor is a recipe for disaster.

In the case of OP, if the system has any kind of pressure in it, on a 2002my, that's the equivalent of winning the HVAC lottery. I'd just pay an AC tech to do the job right on the first try.

 

This Gen has the pressure switch, relay, fuse and controls in the car. If it's Auto AC, add in a cabin temp sensor.

Ditto low refrigerant.

 

Check ac pressures first as others stated. If it has pressure then it could be a bad clutch coil. Easiest way to tell is to use a test light on the connector that goes to the clutch coil. If you have 12V power when you turn on the ac then this means your ecu is sending a signal and the signal is getting to the compressor. The compressor just isn't engaging the clutch. Could also need a shim/spacer removed but you can use a feeler gauge to check the clearance of the clutch.

 

So as recommended by someone I bypassed the pressure switch quickly to test whether the clutch would come on. However, as I did this, the entire AC system stopped working and the fuse under the dashboard was blown. Quickly replacing this turned the AC system back on, however, NOT the radiator fans. The radiator fan relay and fuses are both okay. It was probably stupid to do the bypass, but does anyone know what could cause the radiator fans to have stopped working , even with a replaced fuse?

 

So as recommended by someone I bypassed the pressure switch quickly to test whether the clutch would come on.

The pressure switch is normally closed if the refrigerant charge/pressure is within a range. If it's outside that range, the switch is open. In the attached wiring diagram from the 2002 FSM, the switch has a two wire connector, and controls the power to the AC Relay and compressor clutch. If the concern is refrigerant charge, check the resistance between the two contacts in the connector on the pressure switch (not the wiring harness connector). If it measures a short (or close to it) the switch is closed, the pressure is satisfactory, and the switch will not affect compressor operation. If it measures high resistance, it's open, and that's probably low refrigerant, or in rare cases, a faulty pressure switch. In the latter cases there's no point looking or testing elsewhere, until this is rectified.

Also, in an earlier post, it was suggested to measure the voltage at the compressor clutch connector when the AC is switched on (engine running). If there's system voltage, then the pressure switch and relay are good.

Also attached is the radiator fan wiring diagram. Note that there's more than one fuse involved with each fan.

 

Did you bypass to ground? Or just across the contacts? Somehow it sounds like you shorted to ground, which is the only way you’re going to blow a fuse.

 

Not sure. I might have accidently.. At this point, the main priority is to get the radiator fans back to work

 

The bypass was just a test to determine if your compressor is working.
Have you got the pressures checked and done proper?
Did you do this test while the engine was at running temp or still cool? I'm not certain that the fans would come on until the engine was at least to running temp. I could be mistaken here.
Check the connector plug for the fan in question and make sure it is connected? If it is, unplug and see if you get a voltage with a meter while the AC is on, but don't do that until you have your lines charged right. Don't forget the oil in the AC charge if you are not having a shop do it. You could ruin your compressor if it is not properly charged and oil filled, not to mention what moisture may be in the system etc.
You could disconnect the fan in the meantime and plug a 12V source up to it to see if it will turn on by itself sans AC and rule out a bad fan. If it runs like that, then you may have a bad relay. This would also be a cause of not having a voltage at the plug when the AC is turned on, of course if the engine is up to running temperature and the fan is otherwise supposed to be on even if the engine is not up to temperature.

 

If it was my car, I'd roll the dice and just add refrigerant. Not many dollars lost if it is a more serious problem. My daughter's 2004 Honda's AC quit 2 years ago. Her BF added a can of R134, been fine since. Not guaranteeing it's the fix, but if my car wouldn't start, I'd first confirm there was gas in the tank...

 

That's a good point, i.e., which fans should run when the AC is on.

Based on the chart below, which I believe applies to 2002, when the car is stopped or at low speeds, both fans should be on when the AC is running. However, I don't have a Gen 3 to verify.

 

That was something I wasn't certain of at all. If the engine is not hot enough, if any either fan would be on.
According to the chart, they both should be so long as the compressor is on. I think even if the low pressure switch was jumped, as the OP did to test the compressor engaging, fans should have come on, barring there is no difference between the generations for this information.