7010 air conditioning

skipmarcy · Jun 5, 2010

jwcinpk said:
My brother came today and checked it out. He says it is the high pressure switch going bad. The high pressure switch is made on the accumulator dryer. He showed me I could make it run but it's just gonna get worse.
After it cycles a number of times the switch shuts it off. Once I notice the warming of the air I can put a hot wire to the compressor to engage it (then take it away) and it will run normally for a while longer.
Hope this is gonna be covered under warranty!

If the switch is in an accumulator/drier this is in the low side of the system and this switch cuts the comp out when pressure is too low, ie either restricted flow thru expansion tube or low refrig charge or bad airflow across the evaporator. If the switch is located in a receiver/drier it is located in the high side of the system which kills the comp when high side pressure gets too high - many causes - poor airflow across condenser, too much refrig in system, badly blocked expansion tube or valve etc. If it really is in an accumulator (low side) you can jump across it to run the comp continually and you'll see your low side pressure drop below mid-20 psi range. If you'll look at your gauges you'll see a temp reading coinciding with the pressure scale for each of the different refrigerants - this is the temp of the refrig at the evaporator. If you're dropping pressure the temp drops and the evaporator can freeze up what moisture is in the air. That's why one will cool some when the comp first kicks in then quit blowing cool until the comp cycles off and the evaporator warms back up and the switch kicks it in again. It is not recommended to jump across a high pressure switch except quickly, strictly for diagnosing a bad switch. Virtually all a/c systems use approx a 5/16" line in the high pressure side and approx. a 13/16" line in the low pressure side of the system - you should be able to confirm which side your switch is located in from the line size feeding the unit the switch is mounted to. If your low side is truly reading around 45 psi at idle with the comp running constantly (jumped switch) I would recommend running the engine up to the high idle (about 1100 rpm) and see what it reads. If it's still around 45 psi, you either have a stuck open expansion valve or too much refrig in the system. If the reading drops down below about 25 psi or lower you can try adding a few oz's of refrig to see if you can get the reading back up towards 28 psi (+/-0). If not, check into airflow across the evaporator (mouse nests really block evaporators !!) or be prepared to open the system and check the expansion valve or tube. Good luck with it !!

jwcinpk · Jun 6, 2010

He had gauges on both sides. Drained some refrigerant, added some, on and on. He said he likes 30 lbs. on the low side and he got it there. It runs fine for a while and then quits. He's a Ford technician and has a few years experience working on AC systems.
I'll check the size of the line and post.

jwcinpk · Jun 8, 2010

Well it's definately a receiver dyer with the switch made on it, Has a sticker on the side that says so anyway. Making it on the high pressure side. At high idle I'm still over 40 psi. Which seems a bit much even by what he was saying.
Air ran great for over an hour today and then all of a sudden just quit again. Can jump to the compressor and it will run a while and kick off. Sometimes it cycles again and sometimes not. Seems odd to me for that switch not to fail completely all at once.