A/C Hi-pressure sensor?

Doing a search, I found a post that matched my a/c problem, which is the comp. clutch running for three seconds, off for six seconds and repeating in this cycle. Unfortunately, the author of the post quoted below hasn't been on the board lately:

"The frequent cycling A/C is not normal. Two problems,
freon just a tad low and the high pressure sensor bad.
It goes from one extreme to the other, not enough
pressure-bam too much pressure. It isn't t sensing any
inbetween pressures.

Jim"

I have a '97 Cherokee. I was wondering if anybody could let me know where the hi-pressure sensor is located and whether you can get it at any chain parts store. I don't want to just dump freon in there, since the pressure seems to be correct as it is. Any help would be greatly appreciated.

Thanks,
Mike

Doing a search, I found a post that matched my a/c problem, which is the comp. clutch running for three seconds, off for six seconds and repeating in this cycle. Unfortunately, the author of the post quoted below hasn't been on the board lately:

"The frequent cycling A/C is not normal. Two problems,
freon just a tad low and the high pressure sensor bad.
It goes from one extreme to the other, not enough
pressure-bam too much pressure. It isn't t sensing any
inbetween pressures.

Jim"

I have a '97 Cherokee. I was wondering if anybody could let me know where the hi-pressure sensor is located and whether you can get it at any chain parts store. I don't want to just dump freon in there, since the pressure seems to be correct as it is. Any help would be greatly appreciated.

Thanks,
Mike

I left several posts regarding the A/C system. To check the charge, you can buy gages for high and low sides, if you want professional diagnosis ($100 plus adapters). However, you can just buy the recharge kit with a low side gage if you want to just add R134a ($40).
The 97 uses R134A and the low charge pressure switch is by the right side firewall on the receiver dryer. Always add charge to the low, suction side.

I left several posts regarding the A/C system. To check the charge, you can buy gages for high and low sides, if you want professional diagnosis ($100 plus adapters). However, you can just buy the recharge kit with a low side gage if you want to just add R134a ($40).
The 97 uses R134A and the low charge pressure switch is by the right side firewall on the receiver dryer. Always add charge to the low, suction side.


Thanks for the info. I have a recharge kit already, and the pressure on the low side seems ok. I was pretty sure the constant cycling of the a/c clutch wasn't right, though. You mentioned the low charge pressure switch... do you think this is most likely the problem? I'm just a little confused as to whether the high pressure sensor is the problem (from the post I quoted) or low charge switch, as you mentioned, or if they're one and the same.

Thanks,
Mike

Thanks for the info. I have a recharge kit already, and the pressure on the low side seems ok. I was pretty sure the constant cycling of the a/c clutch wasn't right, though. You mentioned the low charge pressure switch... do you think this is most likely the problem? I'm just a little confused as to whether the high pressure sensor is the problem (from the post I quoted) or low charge switch, as you mentioned, or if they're one and the same.

Thanks,
Mike
Sorry about the confusion...what year is yours? R12 or R134a?
What happens is there is a low pressure switch...which protects the system when there is a low charge. In an AC system the low and high sides are related...if the low is low(under charged) then the high is low too....there is no high side switch only the low pressure switch.

If the compressor does not come on (common problem due to electrical issues) there is no high and low pressure differential....so pressure is equal...about 100psi. When the compresor is on... the low is about 30 psi and the high is about 200-225psi in a R12 system. There is a valve that controls this.

Cherokees including mine which is a 97 has an electrical problem to the AC compressor at the weather pack which is under the compressor on the RH side on the engine.....which causes intermittent operation. I was also a dealership tech on other brands and worked on AC professionally.....usually you have to use the gages to diagnosis the problem properly.

I hate those charge kits. You can't tell your state of charge with just a low side reading other than it is empty or way over charged.

I hate those charge kits. You can't tell your state of charge with just a low side reading other than it is empty or way over charged.

That is why I use the one that has a gage marked with PSI and color coded....psi reading reads from 0 to 100 psi....correct charge is 30-34 psi. (Although the gage says it is OK from 28 to 42 psi. With compressor running of course.)

You can't alter the high side anyway. You can always pay for the two gage manifold unit if you work on AC all the time. I had one of these when I worked in a shop. You also need an evacuation unit to remove the r134a plus a vacuum pump to remove moisture if you open it up.

Alohabra,

Mine is a '97 with the 134A. The compressor is working, it just seems like it's cycling too much. With the gauge on the low side, it reads where it should be, then for three seconds when the clutch kicks in, the reading falls low (as it should, I guess) then raises back to where it should be until it repeats itself. It follows this exact cycle. I haven't added any freon yet, because according to the gauge, I'm at the upper allowable pressure as it is. This is what leads me to believe the problem is something other than a low freon level. I guess I can add a very small amount of freon and see if that works. If it doesn't, I guess I'll have to take it to the pros, unless you know of any other testing I could do.

Thanks,
Mike

I just read Saudade's post on another thread, where he mentioned if the freon level is too low, the low switch will prevent the compressor from working properly. I think I will try to add a small amount of freon and see where that gets me.

Mike

I just read Saudade's post on another thread, where he mentioned if the freon level is too low, the low switch will prevent the compressor from working properly. I think I will try to add a small amount of freon and see where that gets me.

Mike
Does your gage has the psi markings?

Like I said in another post...I have had intermittent problems with my 97 Sport due to poor electrical connection causing the compressor to cycle off at times. When the compressor clutch does not have enough voltage (or amperage) the clutch wouldn't pull in because the magnet is too weak.
I would revisit this area...I have done mine three times since January.
I am going to solder this wire together or use a relay (oh extra work).
Brother has my Jeep right now anyway and he is Jeep tech, maybe he will fix it.

Oh yeah...You can take the connector off of the low pressure switch and jump it with a paper clip and clean the male contacts also. Try that.

Well, I got lucky this time. As soon as I started to dump some freon in the system, the clutch kicked in and the compressor stayed on, no more on/off cycling. My gauge does have the PSI marks with the colored fields, so I filled it to the right range. I just needed 1 and a 1/2 cans to get it filled up. It blew cold right away, which is nice, since it hit about 98 today in St. Louis. Unfortunately, when I restarted the car later, I had the most hellacious belt squealing I've ever heard in my life, and it happened intermittently only when the a/c settings were on and I was idling or at very low speed. Guess I'll get that belt changed tomorrow, since the Jeep's new to me and who knows how old that belt is.

I really appreciate the help with the tips, and now I'll know what to keep an eye on in the future with a/c problems.

Mike

Well, I got lucky this time. As soon as I started to dump some freon in the system, the clutch kicked in and the compressor stayed on, no more on/off cycling. My gauge does have the PSI marks with the colored fields, so I filled it to the right range. I just needed 1 and a 1/2 cans to get it filled up. It blew cold right away, which is nice, since it hit about 98 today in St. Louis. Unfortunately, when I restarted the car later, I had the most hellacious belt squealing I've ever heard in my life, and it happened intermittently only when the a/c settings were on and I was idling or at very low speed. Guess I'll get that belt changed tomorrow, since the Jeep's new to me and who knows how old that belt is.

I really appreciate the help with the tips, and now I'll know what to keep an eye on in the future with a/c problems.

Mike

UH..don't replace serpentine belt yet...Just tighten the the idler pulley...

There are some posts about that....

UH..don't replace serpentine belt yet...Just tighten the the idler pulley...

There are some posts about that....

Yeah, I was going to replace it anyway as a maintenance thing. Do you happen to know whether the '97 belt is a bolt-tighten or self-tensioning pulley? I thought I read there were a couple of different designs....

Manual tighten....loosen nut in front ...then use 15mm socket for the long bolt that tensions the belt....add about 1 to 1.5 turns and test.

Retighten front nut when done. If bearing is worn replace the whole pulley or press in a new bearing. I made a post about this about a month ago.

Hey, glad to have helped. :)

AlohaBra makes a good point regarding the gages. If you're going to service things yourself, you do need to get some decent tools. You don't need to go overboard but don't cheap out either.

The real issue is understanding enough about how it all works so you can properly diagnose the problem and having the tools to do it properly.