Electrical problem with Air Con.

[ticky]

Hi
I’m wondering if anyone has encountered this problem before

This is an Electrical Problem.
I have no power to the compressor. I have tested pressure switch and that’s not the problem. I have checked the fuse and swapped out the relay.

I have a gut feeling it is in the switch on the dash but I have nothing to back that up and I wouldn’t know how to test it, my electrical skills are not that great.

Has anyone had this problem.

Thanks

Steve

[Dicko1]

Check all the fuses. Sometimes the one fuse is used for multiple accessories.

[erad]

I don't know about the later model Pajeros, but the earlier ones used to require the cabin fan to be running before the A/C compressor would be powered up. I imagine this is still the case. Sometimes the fan resistor used to burn out. This meant that the fan would not run on anything other than fastest speed (when the resistor was bridged out). Check to see if the A/C compressor runs when you have the fan speed at maximum. If it does engage then, probably the fan resistor is stuffed.

[old Jack]

Check Condensor Fan (the electric fan in front of the radiator) is turning ON when AC is selected ON, if not working then check Fuse 10 (25A) in the Engine Bay Relay Box.

Check the AC Compressor Magnetic Clutch Relay fuse in the Engine Bay Relay/Fuse Box, Fuse 19 (30A). Also check the earth wire from the clutch to the compressor body is all good.

Erad is close with his thinking, but on the Gen 4 there is a ECU controlling the cabin fan motor speed rather than the old resistor block, but the fan still needs to work!
If not check the Blower Fan Relay Contact fuse, Fuse 19 (30A) and the Blower Fan Relay Coil fuse, Fuse 5 (7.5 A) both are located in the cabin fuse box.

OJ.

[ticky]

Thanks Erad and OJ.

Firstly, the Cabin fan works fine, so thats not the problem, but thanks for the suggestion.

OJ, Ill check out those fuses and relays etc, and if that doesnt fix it, Ill take it to Eddy the Expert. Any Suggestions on where I should take it, or should I just go to Portside Mitsubishi.

Thank

Steve

[old Jack]

I have lost confidence in Portside Service Department after an incomplete service and a very poor response from the Service Manager.

Check fuses as per my instructions and let me know how you go. If required I can give you the next stage of checks to do or we could catch up early next week.

OJ.

[erad]

How did you test the pressure switch? The contacts should be closed if the compressor clutch is to operate, is the resistance across the switch terminals should be zero.

[ticky]

I checked the fuses as suggested by OJ, and all are good, however, the condenser fan is not coming on.

The Cabin fan is working fine.

This has been an intermittent problem since about December, but it would never stop working long enough to try and track it down. When it was working, it would work fine for weeks at a time, and was icy cold on the hottest of days. It now seems to be a Permanent problem.

Actually, I didn't check the Pressure Switch, I checked the wires running to it and two of the three had power.
I will check the pressure switch to make sure there is continuity there. I don't believe this is a gas problem but I suppose the switch could be faulty.

As it was an Intermittent problem, the Earth wire could be the problem, a bad earth, now no earth, but I cant see down there to even find the wire without lifting out the battery, & I cant do that.

If it was a bad earth or no earth on the compressor, would that stop the Condenser fan from working?

Similarly, if there was a problem with the Condenser Fan, would that prevent power from getting to the Compressor?

If I dont get it sorted out by the Weekend OJ, Ill take you up on your offer to help me with it. Thanks.

Steve

[erad]

The pressure switch is supposed to operate for low pressure or high pressure. At this time of the year, you are not likely to have high pressure in the gas system, but you could have low pressure. Since there are 2 power sources going to the switch (high pressure, low pressure??) I guess that the other wire will be earth. If this is the case, maybe it requires 2 open circuits for the compressor to cut in. This is not what I would normally expect - I think that the switch should be closed for the compressor to operate.

[ticky]

Hi Erad.
While I believe it is possible the pressure switch is faulty, I still haven’t tested it, only the wires going to it.
I don’t believe this is a gas problem, in fact, I am confident it is not a gas pressure problem.
If it was, then the pressure switch would create an electrical problem like I have, but I gas problem would have produced its own set of symptoms when it was working, especially in summer.

I believe this is totally electrical.

Years ago, I used to be in Auto Air and I could fix this, but with the modern cars the electronics is far too complicated for me

[old Jack]

The AC Compressor Clutch is powered through the AC Compressor Relay and the Condensor Fan is powered by the AC Condensor Fan Relay. So next thing is to check the input and output voltages of the relays.

OJ.

[ticky]

Thanks OJ,
Ill have a go at that. Not 100% at the moment so it might be a few days before I get to it.

Steve

[ticky]

Ive Checked the Relays

The AC Compressor Clutch is powered through the AC Compressor Relay and the Condensor Fan is powered by the AC Condensor Fan Relay. So next thing is to check the input and output voltages of the relays.

OJ.

I have checked the Condenser Fan Relays in the Engine Bay Fuse Box, and they are fine. By powering the dead side of the relay socket, the fans work fine. I also discovered there is supposed to be 2 horn relays, not 1, but thats not the issue.

Next I removed the lid of the little square relay box in the engine bay and tested the relay. By powering the coil, I could feel it pulling in and releasing when un-powered. I didnt have enough hands to check for continuity between the other tow terminals, but I di chek the voltage in the Relay Socket. The power to the coil is only about 6.5 volts with the air conditioner turned on. This is not enough to pull in the relay. I powered the pin in the socket that goes to the compressor, and the compressor clutch pulled in.

So at this stage, it loos like the Compressor Relay in the little Square relay box is not getting 12 volts, only around 6v.

Any Ideas where to go from here?

Steve

[old Jack]

Sounds like you need a volt multiplier, I reckon a X2 should be about the right size!

OJ.

[nj swb]

Steve, the coil of the compressor relay is negative switched i.e. it has a permanent 12V on one side, and the other side is switched by a solid state device.

Which side of the coil did you measure the 6.5V, and what voltage was on the other side?

Are you 100% certain that you have sufficient gas? A simple pressure switch isn't sufficiently complicated for modern vehicles - they needed to make it harder. The schematics show the gas pressure sensor is a three wire device - +5V from the A/C ECU, grounded via the ECU, and the third line is presumably a pressure signal. If the signal wire is high, is that good or bad?