AC compressor clutch not kicking in

[m1tch]

Hi all,

Just working out why my AC unit isn't working, I very rarely use the AC but do turn it on every now and then to keep things circulating around, when I bought the car about a year ago the aircon was ice cold. Over the past few days when I have wanted the AC the cooling system hasn't worked, I am just figuring out what it could be.

• I have checked the fuse behind the glovebox - which is fine
• When this fuse is pulled the AC button doesn't light, when you plug it back in it does light
• I have checked the connector to the clutch on the AC compressor and its not getting 12v with the AC button pressed

 

I am guessing its either:

• AC relay (if there is one)
• Dashboard button issue (that lights but doesn't send 12v to the clutch)
• Something else in the system

 

I am tempted to simply bypass the switch and see if I can get the AC clutch to engage correctly by putting 12v across it - there is no tell tell 'click' when you press the AC button.

 

Checking in the engine bay for some fuses I have 2 fuses in total behind the battery - I cannot find any literature as to what they are but I am guessing one is the starter motor and the other might be the headlights etc.

Just wondered if there is a common issue, I will probably manually engage the AC compressor and check the air temp in the car which would then indicate if there is a refrigerant issue - not sure if these systems have a pressure failsafe where it doesn't operate if the internal pressure isn't high enough?

[chemfusion]

1 hour ago, m1tch said:

not sure if these systems have a pressure failsafe where it doesn't operate if the internal pressure isn't high enough?

Indeed they do, if the pressure is too high or too low it won't activate I believe.

There is an AC relay in the relay box next to the battery. When I was troubleshooting mine I bypassed it with a bit of wire and the AC kicked in - the relay itself was fine though, it was a section of wire that had broken off from the connection to the pressure sensor on the high pressure side of the system that was making it believe there was something wrong, the circuit was open when it should have been closed or vice versa

My post here was what I did, it might be of inspiration 

 

[Tdci-Peter]

3 hours ago, m1tch said:

AC relay (if there is one)

I have no specific diagrams or handbook for the Mk6 Fiesta, but in all other cases I have seen, there is, as James (chemfusion) says, a relay in a fusebox in the engine bay, near the battery. There should also be a fuse for the solenoid here.

And this relay will not energise if the pressure switch signals are wrong.

 

[m1tch]

6 hours ago, Tdci-Peter said:

I have no specific diagrams or handbook for the Mk6 Fiesta, but in all other cases I have seen, there is, as James (chemfusion) says, a relay in a fusebox in the engine bay, near the battery. There should also be a fuse for the solenoid here.

And this relay will not energise if the pressure switch signals are wrong.

 

 

9 hours ago, chemfusion said:

Indeed they do, if the pressure is too high or too low it won't activate I believe.

There is an AC relay in the relay box next to the battery. When I was troubleshooting mine I bypassed it with a bit of wire and the AC kicked in - the relay itself was fine though, it was a section of wire that had broken off from the connection to the pressure sensor on the high pressure side of the system that was making it believe there was something wrong, the circuit was open when it should have been closed or vice versa

My post here was what I did, it might be of inspiration 

 

Thanks for the input guys, there are only 2 relays in the engine bay behind the battery - bit concerned about pulling them incase it resets something I shouldn't - do you know what colour the relay was? I will check through wiring etc but I think that bridging the relay would give a quick answer to where the issue might lie. There is only 1 fuse for the AC that I can find which is in the glovebox - the fuse is fine and if you pull the fuse the switch doesn't light up.

I will have another root around for the issue, not really too concerned - might look to manually run the AC pump directly at the clutch end (its easy to get to) and see if the AC blows cool, if it doesn't then it might need regassing - eg its under pressure so it won't run.

[Tdci-Peter]

5 hours ago, m1tch said:

might look to manually run the AC pump directly at the clutch end

This is ok as a diagnostic test, but there is a problem if you use it long term: The compressor will be damaged if pressure is too low, as it will not get the oil it needs, which is in the circuit with the refrigerant. That is why the pressure switch is there. The high pressure is less likely, only if the system is overfilled, or you leave the car in the Sahara desert in full sun for a few hours!

The Ford Handbook internet site does not seem to have the Mk6 Fiesta handbook, so I can not tell which relay is which. Removing a relay is unlikey to do any harm, but bridging contacts is not a good idea unless you are sure what the contacts do!

The a/c clutch normally uses a 10A fuse. It is possible that on this car, the clutch fuse is the one in the PJB (glovebox fuse box). Need the manual, really.

Peter.

[m1tch]

3 hours ago, Tdci-Peter said:

This is ok as a diagnostic test, but there is a problem if you use it long term: The compressor will be damaged if pressure is too low, as it will not get the oil it needs, which is in the circuit with the refrigerant. That is why the pressure switch is there. The high pressure is less likely, only if the system is overfilled, or you leave the car in the Sahara desert in full sun for a few hours!

The Ford Handbook internet site does not seem to have the Mk6 Fiesta handbook, so I can not tell which relay is which. Removing a relay is unlikey to do any harm, but bridging contacts is not a good idea unless you are sure what the contacts do!

The a/c clutch normally uses a 10A fuse. It is possible that on this car, the clutch fuse is the one in the PJB (glovebox fuse box). Need the manual, really.

Peter.

Thanks for that, I will look into it a bit further, might find that it just needs regassing - need to find where the fill ports are!

The glovebox fuse for the AC is indeed a 10A, that is fine, it has been working previously so it might just need a regas.

[iantt]

Normally it's just a regas. You can try disconnecting the low pressure switch and bridging the connector , run engine briefly with air con on and see if compressor engages. Don't leave it running to long like that though.

[m1tch]

1 hour ago, iantt said:

Normally it's just a regas. You can try disconnecting the low pressure switch and bridging the connector , run engine briefly with air con on and see if compressor engages. Don't leave it running to long like that though.

Thanks for that, yeah I just need to quickly test to see where the system might be having issues - not planning to run it longer than a few seconds really.

[leoalayola]

Hello!

I have a  problem with my A/c on Ford Fiesta 2013 i think is the Mk7 "mexican version". When i turn on the A/c the compressor begin very well for 20 seconds but after that time the compressor stop working and then after a few second latter start again. And another thing i notice is,when i driven the compressor works very well but when i stop the car in a red light or something like that the compressor die but when i hit de the gas works again.

I appreciate the help and sorry for me english it's very rusty.

 

 

 

[Tdci-Peter]

21 minutes ago, leoalayola said:

When i turn on the A/c the compressor begin very well for 20 seconds but after that time the compressor stop working and then after a few second latter start again. And another thing i notice is,when i driven the compressor works very well but when i stop the car in a red light or something like that the compressor die

Is the Fan behind the condenser working? (Radiator fan). It should be on whenever the a/c is on. If not on, the condenser will get too hot to work, and the a/c will shut down.

 

[leoalayola]

1 minute ago, Tdci-Peter said:

Is the Fan behind the condenser working? (Radiator fan). It should be on whenever the a/c is on. If not on, the condenser will get too hot to work, and the a/c will shut down.

 

Yes, the fan work perfect, there is NOT overheat from the engine, is just the compressor that worksr for a few second then stop and start againg and then stop and so on...