I replaced the AC in the beginning of the summer and everything was good. I just noticed that when you select upper vent or defrost on the heat controls that the rad fans run continually and the AC clutch engages steady. I'm pretty sure before the AC would cycle in and out when the defrost setting was selected and the fans would only come on when the car got hot. A couple of other pieces of information. 1) the check engine light has been on for years and I believe the code says something like output coolant temp doesn't match output temp 2)radio light no longer works(only relevant if some sort of short but thought I'd include it). ideas?

 

The radiator cooling fans should always run while the a/c compressor is running. Your fans may have been previously cycling, because the a/c compressor was shutting off. Defrost also uses the a/c compressor to dry the air to remove moisture from the windshield. I'm not sure if Honda has the a/c running when you select the upper vents.

I think your a/c system is functioning normally. You could put pressure gauges on the system to verify the a/c system is running properly.

As for the check engine light, it is likely not related to the a/c system. You can stop by an autoparts store and have them scan for codes. Post the actual code on here and we can give you some suggestions to try.

 

Okay so the A/C compressor should be running all the time as well as the cooling fans if the vent selector is on the last 3 settings (feet, feet/defrost, defrost) or if the AC is engaged? This happens even with the key just on and the car not running. I don't remember that being the case before, the fans make a lot of noise and thought I would have noticed that. I have an OBD reader that connects to my laptop, codes are as follows:
P2185 Engine Coolant Temp Sensor 2 Circuit High
P2183 Engine Coolant Temp Sensor 2 Circuit Range/Performance
P0128 Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature)

P0128 is the code I had before when I last checked but the other 2 weren't there.

I removed the relay for the AC and fans still run as per the above.

 

Parts of the system are working correctly, namely that AC is active to remove moisture from the air when it's directed to the windshield.

But I don't think the AC compressor should ever run 100%. It should cycle, controlled by the the evaporator temperature. Some reasons for it to run constantly include low refrigerant charge, or faulty evap-temperature measurement. You can check by watching the compressor clutch as it cycles on & off.

But it sounds like the radiator fans are running constantly, but not necessarily the AC compressor running constantly. I don't have a wiring diagram for your car; but with the AC relay removed, I think the fans must be running because of a faulty coolant-temperature measurement or some problem with that circuit.

 

Is your accord a 4-cylinder or v6 engine?

The engine coolant temperature sensor 2 is on the bottom and driver's side of the radiator for a 4-cylinder engine. Make sure that sensor is plugged in and look at the wiring and connector for signs of damage or corrosion.

Does your obd2 scanner give you live data? Look at the value for the coolant temperature sensor 2 if your scanner is capable.

 

Jim, the AC does not cycle in and out, the compressor is running continually. I'm pretty sure it used to cycle. Should the fans be running with the engine cold with the key on but engine not running?
PAhonda, it is a 4 cylinder and the wife has the car so will check when it returns. I'm not sure the software monitors real time but I'll check that as well.

 

With the AC relay in place (and nothing faulty), the radiator fans will run with the AC compressor IF the HVAC is directed at the windshield (or windshield-floor-mix). Even with a cold engine, the radiator fans will cycle with the AC compressor. If something (low refrigerant, etc) causes the compressor to run constantly, then the fans will also run constantly.

Without a wiring diagram I'm speculating about the rest...
With the AC relay removed, the radiator fans should not run until the engine is hot. Same thing if you have the AC turned off and the HVAC directed to the floor. In fact, they normally don't run until the coolant-temperature is a little above normal. If the fans are running with a cold engine and the AC relay removed, then I think you have to look at the circuits that control the fans based on coolant-temperature. And beginning about 2001 that system includes ECM programming. Older Accords had a fan-switch that was not related to the dashboard gauge or the ECM.

I'd look at the wiring diagram to see if there are fan relays in addition to the AC relay.

 

I took the bottom shroud off to look at the wiring on the temp 2 sensor and it looks okay. My software does have real time monitoring but not specific to the actual sensor. The temp seems to stay at 72 degrees celcius and the fans do not engage on the first 3 control settings. Can you recommend a PC software to use with my USB OBD that would monitor the individual sensors?
Digging a little further I put the AC relay back in and when AC was called for the compressor ran steady. I checked the pressure and it was low, must be a leak but lasted all summer. After topping it up the AC started cycling in and out and the issue with the fans running all the time went away. It looks like even if you remove the AC relay, the cooling fans run if the control is set to defrost or an AC call is made. This seems abnormal to me. Last year the AC compressor seized so I removed the relay and I'm sure the fans didn't run like this. The only thing I can figure is that the AC system still has pressure so it didn't trigger the fans to run. I'm just not sure at this point how this all works or is supposed to work.

 

I don't think the a/c computer can tell if the compressor is actually running/receiving power, so it must default to command the radiator fans on. My Acura TSX fans would run if I had the key in the II position, not start the car, and have the a/c turned on (almost all the time in Texas).

 

Okay thanks for all the help. It looks like i just need to track down my AC leak. I guess the temp 2 sensor also needs to be replaced. Do I have to drain the coolant? Anyone have a part number?