So two weeks ago I had the compressor / dryer changed on my car. AC was ice cold. A week later my AC went from ice cold to just cool.

Today I had time to open the hood, I notice the fans arent coming on at low speed but they are at high speed. If I kick the AC on teh fans arent on.

I took it to the mechanic for a quick look (no appointment just a quick look) and he had a look at the relays and they seemed fine. He thought maybe a fuse but couldnt find what it would be, what we checked was fine. He only had wiring scheme for 1999 max and mines a 2k, are they the same ?

So my question is before I take it to him for a look properly what can I try first ? Hopefully its simple. I replaced the fans a little over a year ago as one never kicked on. I presume the fans motors are fine etc as they do operate on high.

All info appreciated, thanks.

 

Try the coolant temperature sensor.

 

Coolant temp sensor is just for the engine is it not ? Those fans come on high when hot to cool it. Itd the low speed that comes on for ac compressor isnt it ? When thv compressor is on rhe fan goes off

 

The fan control circuits for the 1999 (4th gen) and the 2000 (5th gen) are not the same, so using the incorrect wiring diagram will only confuse things.

There are 2 fuses for the radiator fans. One fuse supplies power for one of the fan motors. The other fuse supplies the other fan motor. So if the fans run at either speed, the fuses are OK.

I'm somewhat confused by your statement on the fans. The fans are supposed to come on on low speed when you turn the a/c on.

Without the a/c being turned on, the fans won't come on until the engine temperature gets up to 200º F. This would be low speed at 200º. When the engine temp gets up to about 220º, the the fans kick into high speed.

There are 3 relays for the radiator fans. Cooling Fan Relay 1 makes both fans run on low speed. Cooling Fan Relay 2 is for high speed on only the fan closest to the battery. Cooling Fan Relay 3 is for the other fan, high speed only.

These 3 relays are the same relay, so you could swap relay 1 with one of the others. The relays are in the box between the battery and the headlight and are labeled.

The a/c compressor will not come on if the outside temperature is below 35º F, but Texas is getting up over 35º.

But the fans not running when you turn on the a/c is a problem for the air conditioning system. The reason for the fans to come on with the a/c being turned on is not for engine cooling. It is to cool the R134A refrigerant for the air conditioning after it has been compressed by the a/c compressor. Mounted in front of the radiator is the air conditioner's condenser coil. If you don't have any air blowing through the condenser coil, the a/c will not cool the car very well.

The a/c is probably fine. You have to get the fans working.

 

Im just going on a past experience with my fans kicking on high but low speed wasn't working properly. I had the temp sensor replaced and low speed seemed to be fine afterward. I was told the the coolant temp. Sensor can have an influence on the fans. This may be different in your case but was the case on my 3rd Gen. I was merely just putting the suggestion out there based on a solution that had worked from a past problem I had like that.

 

It seems to me that it's possible for the ECTS (Engine Coolant Temperature Sensor) to cause the radiator fans to not work properly.

The ECTS reports the coolant temperature to the ECU which uses the info for several things. The ECU sends the signal to energize the cooling fan relays, so if the ECTS is not accurate, the radiator fans won't be turned on and off at what is really the correct time/temperature.

Nissan used the same same temperature ranges for fan operation on the 3rd, 4th and 5th gens. I've never checked the 6th and newer gens, but I would bet it's the same.