Talca

On some trucks (depending on software level in the engine ECM) the dealer can go in to the Engine parameters and uncheck the "air conditioning installed" . This way the Engine ECM ingnores the signal from the A/C high pressure switch and the fan should stay off if the problem lies with the A/C switch. However the 1999 CX I was working didnt have this feature but most newer trucks (2002 I think) do. The dealer should be able to use the laptop to check whats going on unless it is a bad Engine ECM. Does you dash have the fan override switch on it? If your truck has the APADS A/C system this could be the main problem. The APADS is a small square electrical box/ECM that is bolted near the radiator and has flashing lights to tell you the A/C is not working. The wiring on the APADS is so screwey that we always remove them and throw them away.

I called into the dealer yesterday there auto elec bypassed the aircon switch which made no difference but it could still be a faulty wire in the loom somewhere. So I have booked it in for the end of next week and hopefully they can solve the problem.It does have a fan override switch on the dash but no APADS. Thanks Again..

had a 1999 Etech in a CX today and the Horton air fan was coming on and off constantly. The water temp was only 180 degrees and the A/C was turned off. Hooked up the laptop and went to "switch status" and could see the A/C pressure coming on then off and the "Fan engage" was doing the same, this will happen even if the A/C is not turned on. Turns out it was a bad A/C high pressure switch. I also looked at the coolant temp and intake manifold temp on the laptop as if these get to high it will also engage the fan. Fuse 41 sends 12 volts to the fan solinoid the it returns back to the Engine ECM where the Engine ECM will ground the return wire. Basicly the Engine ECM makes or breaks the ground to control the fan clutch. It can be a pain to figure out without the laptop and Mack software.

Thanks for that Mackpro. I will take it back to the dealer again and mention what you said. Is there any way the A/C high pressure switch can be by passed.The coolant temp makes no difference to the problem. have checked fuse 41 as suggested by rhasler and it has power to the air switch on the radiator but no ground.

The way you describe the problem it sounds like it's probably an electrical problem. On the left side of the engine compartment there should be a fuse panel bolted up to the cab bulkhead. This is the EPDM (engine power distribution module). Fuse 41 is located in this box and it supplies power to the fan clutch solenoid. Due to the location of the epdm it had a tendency to get road salt and contamination in it which would cause bad contact across fuses in the box. Take a look at the box and see if the terminals inside look corroded. With the engine running try wiggling the harness coming from the epdm and the harness on the engine as well.

Thanks for your help. I have checked the fuses in the EPDM box.I checked fuse 40&41 again they look clean but hard to see the back of terminals inside box.The problem appears to be electrical because the air switch on the side of the radiator is not getting an earth when the fan is engauged &getting an earth when disengauged.If the fan is engauged and you give it a earth it disengauges as long as you hold the earth.This should eliminate a fan hub problem. thanks again....

I have a 1999 CH with 470 Etec engine. I was on this site a little while ago and had some suggestions to help with my problem but no luck yet.The problem is every time I use the accelorator the fan engauges and when I take my foot off the accelorator most times the fan will disengauge.If I use the cruise control to increase revs the fan stays disengauged .This problem happens weather you are moving or stationary .The dealer has replaced the vechile ECU and all senders that supply ECU. There readouts give no listed faults and the copilot is not showing any faults.Every thing else works perfect. have had auto elecs look and they say every thing tests okay. Some times it will have a good day and the problem is not so bad.This happens weather the engine is hot or cold. thanks for any suggestions....

Check the air conditioner high pressure switch connector in the engine compartment for a loose connection. I have gotten new fan solenoids that were bad before.

I have had a auto elec check the air con high pressure switch which was replaced by the dealer. he said the switch and wiring was all ok but I proberly should get it checked again .Thanks

have 1999 ch fitted with a 470 e7 etec engine. having trouble with the fan engauging every time I use the accellerator pedal then most times it will disengauge when take foot off pedal .the dealer has had 3 goes at fixing it they have replaced the vechicle ECM ,air solanoid ,water temp senser , manifold temp senser ,air con switches .this problem has no relation to water temp.regards hoping someone else has come across this problem.