QuestionMy vehicle (Ford Bantam pick-up, 1.3 Rocam motor) has two pressure switches for the air con system. One is the A/C cyling switch, which if I understand correctly effectively does the temperature regulation, and a "dual pressure" switch (as in double pole more that dual function from the electrical diagram I have: a normally closed contact in series with the cycling swtich, and a separate normally open as a PCM input).
What is the funcition of this dual pressure switch? Its positions are marked as Normal pressure and High pressure.
Would it be best for the cooling fan to run only when the compressor is engaged or should it run continously when the aircon is activated, whether the compressor is operational or not?
Due to mods to this vehicle I had to turf out the original PCM that unfortunately controls the A/C as well, and am now endevouring to get it operational again.
Any advice will be greatly appreciated.
Thank-you,
Justin
AnswerHello Justin
I have pasted your questions in to this section and replied immediately below each section
My vehicle (Ford Bantam pick-up, 1.3 Rocam motor) has two pressure switches for the air con system. One is the A/C cyling switch, which if I understand correctly effectively does the temperature regulation
Answer Correct. An inoperative cycling switch will allow the compressor to engage constantly and icing will usually appear on the low pressure line
and a "dual pressure" switch (as in double pole more that dual function from the electrical diagram I have: a normally closed contact in series with the cycling swtich, and a separate normally open as a PCM input).
What is the function of this dual pressure switch? Its positions are marked as Normal pressure and High pressure.
The function is to control overpressure of the system and shut the compressor out at circa 28 Bar
The 'normal' is to accept 12 volts from the fuse board and the send it to the compressor. If the vehicle has no gas it will not activate and only one side of the switch should have voltage.
Voltage on both side means the switch is active and something further forward has failed
If there is no voltage at at all then there is a problem between the cabin and whatever send the signal to the switch
Would it be best for the cooling fan to run only when the compressor is engaged or should it run continously when the aircon is activated, whether the compressor is operational or not?
Due to mods to this vehicle I had to turf out the original PCM that unfortunately controls the A/C as well, and am now endevouring to get it operational again.
The activity of the condenser fan varies from manufacturer to manufacturer, we are a UK company and not at all familiar with your vehicle and also the modifications carried out may influence the operation of the original system, although most Ford systems here will wait until the sensor says go and then it will run to bring the high pressure side down to about 10 bar
You don't actually say what the problem is with the a/c but as a guide, if it ices then the cycling switch is faulty, if it won't cut in then make sure it has gas and your compressor clutch is working. To find this out disconnect it and give it 12 volts from the battery and see whether it clicks. If not the compressor clutch is faulty, the air gap between the clutch plate and the outer pulley should be about(. point)3mm
