Help Needed - Air Conditioning

[AdsGrandWagoneer]

Hi,
I have an 87 Grand Wagoneer. It has been converted to the new Air Conditioning system R134.
Here is the problem:
When the dash control is swithed to A/C, the compressor does not come on, there is no 'click' and the magnetic clutch does not engage.
There is power going to the 2-wire sensor that is located next to the sight glass, but no power coming out of the sensor going to the compressor.
What does the sensor do? Does it tell the compressor when to cycle off and on?
There does not appear to be anything happening inside the sight glass, no bubbles, no fluid movement.
Thanks for any suggestions.,
Adam.

[ July 23, 2001: Message edited by: AdsGrandWagoneer ]

[Sergio & Ulrike]

I believe that that sensor is a low pressure switch. If the pressure in the system is below a certain PSI then it prevents the compressor from coming on. If this is so you may have a leak that has reduced your refrigerant level below necessary minimum to make the switch or you have lost the charge completely.

[wagdriver]

It is a pressure sensor for sure, high or low, I am not sure of. It is in the high side of the system before the expansion valve, which leads me to believe it is a high pressure cut out. Any way just jump it out and see if the clutch engages, if it does it(the sensor)may be defective. If that lets the clutch work then you need to put a set of gages on the system and see what the actual pressures are. If they are satisfactory, replace the sensor and you should be back in business. ;)

[AdsGrandWagoneer]

Hi,
I jumped the sensor and the clutch engaged....but the A/C did not blow cold. Looks like I have a leak, ****, it worked last week and it is in the 90's here this week.
I'll have to take it into the shop.
Thanks for your help.

[wagdriver]

Did you look at the sight glass? There are two thing to look for. Bubbles, there will almost always be bubbles if the system is functioning. If there are no bubbles then two possibilities exist, 1)low or no refrigerant 2)or an overcharge. That is why I said you will have to put gages on the system to see what is going on. ;)

[AdsGrandWagoneer]

Thanks Wagdriver,
There are brown beads in the sight glass and no bubbles.
I don't have the guages to check the pressure.
The AC worked fine last week and now nothing.
I won't have time to get to the garage until next week. Is there anything else that I can check before going to the garage?
I'll try jumping the sensor and taking it for a short drive to see if it blows cold.
Thanks.

[wagdriver]

You have probably got this fixed by now, but you should not have to drive it to see if the air is going to blow cold. I don't know what the brown beads are but(I'm guessing here) they could possibly be dessicant from the receiver drier. If that is true you will have to change it out and blow out the remaining lines up to the expansion valve to remove the all debris that is in them. It would be a good idea to blow out all the high side lines at this point period. All of the lines from the compressor to the expansion valve. Of course this means loosing all the refrigerant, vacuuming and reharging the system. This is not a common occurance fortunately. :( But it is one that needs to be delt with properly, half measures will not do. When you get it all done you will at least know that it is done right, and should not cause any more problems. ;)