A/C Only blows cold when radiator fan comes on?? plz help

[Callmejc27]

So living on the gulf coast of FLA really stinks when you have no AC and its even worse when it teases yah and only blows cold when the radiator fan comes on which isn't that often only really when your sitting somewhere in idle for about 10 minutes... has anyone ever had this issue ? Thanks a ton


-J

[CTScott]

Sounds like you are low on Freon.

[Callmejc27]

CTScott thank you for your kind reply... i have checked the pressure and level and freon is full! so mind boggling! is there a part, sensor, or switch that the AC system uses to kick the fan on when you turn the switch on in the car?? something is not activating the engine cooling fan when i turn the air on ! IF the fan is on from the car getting "hot" air blows icy cold

[CTScott]

The AC Amplifier (ECU) talks to the ECM via CAN bus, and the control of the fan is done by the ECM. Can you tell if the compressor disengages when the fan is not running?

[Callmejc27]

yes it does disengage when fan is not running...

[CTScott]

Originally Posted by Callmejc27

yes it does disengage when fan is not running...

OK. That would make me think that it is kicking off due to an issue. It may be worth having a dealer or other repair shop with a TechStream tool plug into the car to see if the AC ECU has logged a DTC.

[Callmejc27]

Ok cool ill take it in ... Forgive my ignorance but your referring to a diagnostic check ...? and What exactly is DTC ... lol Thanks again !

[CTScott]

Originally Posted by Callmejc27

Ok cool ill take it in ... Forgive my ignorance but your referring to a diagnostic check ...? and What exactly is DTC ... lol Thanks again !

Yes. The TechStream tool is the Toyota diagnostic system. You can't read the DTC (diagnostic trouble codes) from the AC ECU with a non-Toyota specific scantool (like what would be used to read/reset the check engine light).

Some of the other subsystems the Yaris can be made to flash their indicator lights to allow you to read their DTCs without the tool, but the AC system can't.

[blacks]

@Callmejc27
HI I THINK I HAVE THE SAME PROBLEM SO CAN YOU TELL ME WHAT THE DEALER SAID

[metalshark]

Originally Posted by blacks

@Callmejc27
HI I THINK I HAVE THE SAME PROBLEM SO CAN YOU TELL ME WHAT THE DEALER SAID

The ECU cannot directly turn on the fan. A relay must be used to source that much current. It is unlikely that the relay has an auxiliary set of contacts to notify the ECU when it has failed. On my Yaris the fan comes on every time I turn on the AC.

[CTScott]

Originally Posted by metalshark

The ECU cannot directly turn on the fan. A relay must be used to source that much current. It is unlikely that the relay has an auxiliary set of contacts to notify the ECU when it has failed. On my Yaris the fan comes on every time I turn on the AC.

The ECM controls the cooling fan via a relay (I did not say that it does not have a relay, just that the ECM has complete control over this process). Normally this does happen when the AC is turned on. The AC tells the ECM via CAN bus message that the AC compressor is running (the AC ECU fires the compressor directly, without a relay) and the ECM turns on the fan via the fan relay.

Since the OP's fan and compressor both turn off, my suspicion is that the AC ECU is logging a DTC and shutting down the AC.

[metalshark]

Originally Posted by CTScott

The ECM controls the cooling fan via a relay (I did not say that it does not have a relay, just that the ECM has complete control over this process). Normally this does happen when the AC is turned on. The AC tells the ECM via CAN bus message that the AC compressor is running (the AC ECU fires the compressor directly, without a relay) and the ECM turns on the fan via the fan relay.

Since the OP's fan and compressor both turn off, my suspicion is that the AC ECU is logging a DTC and shutting down the AC.

If the fan relay is an open loop control line then failure of the fan relay will cause high head pressure at the compressor. Pressures too high or to low will cause the ECM to shut down the compressor clutch for system self protection. Many times the fan relay coil will develop an internal short that causes a cyclical thermal related failure that is harder to diagnose because some times it works, and some times it doesn't just like an ignition coil pack.

[CTScott]

Originally Posted by metalshark

If the fan relay is an open loop control line then failure of the fan relay will cause high head pressure at the compressor. Pressures too high or to low will cause the ECM to shut down the compressor clutch for system self protection. Many times the fan relay coil will develop an internal short that causes a cyclical thermal related failure that is harder to diagnose because some times it works, and some times it doesn't just like an ignition coil pack.

If it were the fan relay, the car would likely be overheating, rather than just having an AC issue. In 20+ years as an Electrical Engineer, I don't think that I have ever seen an intermittently shorting relay coil. If it actually did so, it would pop the fuse.

[blacks]

so What the conclusion to the problem guys

[rsoaramud]

conclusion..replace the compressor???......