the truck is a 1986 F 250 diesel I just installed a rebuilt compressor and had the system recharged. It worked fine before I went on vacation for 10 days. Yesterday I gave it a try and no cool air. The clutch is not engaging. I checked fuses all ok. I have tried max and normal. Checked the plug at the clutch. Not sure I am getting power to the plug. It has two terminals is one + and the other -? What I would like to do is supply power from the battery directly to the clutch to see if it engages. How should it be done?

 

i am going to say there is a slow leak in the system and it is now low on charge.

 

That is what I thought so bought some 134A with UV dye in it to see where the leak or leaks are. When I went to recharge, I turned the Ac to max punched the can and the pressure was just below the blue secretion. The clutch was not engaged. If pressure is too low the clutch will not engage?

 

those do it yourself can gauges are as useless as teets on a bull. if the compressor is not running, low side pressure will read good or high on the can gauge and the system will not draw refrigerant into the system.

there are two different pressure switches in the system that control clutch engaging.
you have a low pressure switch and a high pressure switch.
if pressure is too low or too high, the switches will open and not let power to the clutch.
you need to have a manifold set to see what is what when doing AC

 

yes I understand that But how do I test the clutch to see if it is bad or the switch in the cab is bad. It all worked fine after I put in a rebuilt compressor and had it recharge by an AC mechanic Then it set for 19 days and now the clutch will not engage. I did check fuses.

 

Low pressure switch is on/near the dryer. Unplug it, and put a paper clip in the harness. If the compressor comes on the system has no charge. If not, further testing is needed. DO NOT RUN WITH THIS SWITCH HOT WIRED
this is for testing ONLY

 

Thanks that got the compressor working . I put in one 12 oz can with UV dye in it. re plugged the switch and restarted it. Clutch now works. Now just wafting for the dye to show up. thanks for your help. my guess is the evaporator.

 

you will need a black light to see the dye.
and don't be surprised if you do not see the dye. i stopped using it and switched to a sniffer to find leaks.

 

yes have the black light. It does show up on the service port. I still need to take the truck for a drive. Will let you know
thanks

 

for a note.
with dye in the system, check the water draining , if the evap is leaking the dye will show under the car or truck in the water . this caught me several times by the jewels in my dealership tech working days.
also 1986 we still used r12 so i hope you did a full flush of everything and installed a new drier or inline filter before adding r134 . new compressor ? if the old one had failed you could have a lot of metal in the lines,switches and filters not really a just swap it out job under real world repair jobs

 

Could be bad seal at the Schrader valve, got itself cocked from the gauge end when it was removed. ( the gauge)
Sometimes a scratch awl poke in to seat it properly is all you need, other times you need to replace the service port.

If the service port is an adapter for the 134a is the cuprite, might be the cure is to take it off, and put the 12 cap back on.

Charlie is correct about the change from 12 to 134a. pag oil and mineral oil are not compatible, and will make the whole inside of your system turn into chewing gum if not completely cleaned before conversion

 

Hi thanks . I put in another can of uv refrigerant and found the leak. It is the a connector on top of the compressor. Monday I have the AC guy pump out the system put on a new O ring and refill it.

 

service port leaks are a pain to find, that is what made me start using the sniffer over dye.
i found it is easier to just change the schrader valve when they leak.