Need help from some A/C gurus

[vrt93]

Disclaimer: I know very little about A/C systems (enough to fix very basic problems) and I'm going off of logic here.

Rundown of the situation: A/c stopped blowing cold air recently. Fan comes on, but the snowflake light wont. Sometimes, if I leave it on, the light comes on and it will blow cold for a while before shutting off. I noticed the compressor isn't kicking on when the light is off (duhh). Today, after about an hour of driving, decided to hook some gauges up and see whats going on. Noticed that my LP side was at 120 with the ac turned all the way up and steadily climbing. HP was around 120-130.

Now I'm assuming the compressor isn't kicking on because its sensing that the LP side has adequate pressure (or at least isn't dropping below whatever threshold the sensor is set to read). This tells me that, logically, there must be a blockage somewhere in my LP line, either the compressor, evaporator, or dryer, and its preventing the LP side from building pressure. Seeing as my compressor will kick on, and works, I'm assuming I need to change either my dryer or my evaporator?

 

[DavidC]

Don't know much about 07 system but I can tell you without the clutch engaged the system will equalize and you will read the same pressure on both ports. With the clutch engaged the LP side will be somewhere around 35 so I think it is more of an electrical thing. You could ohm across the 2 pins of the LP switch and the HP switch if the 07 has those. LP switch is normally open and HP is normally closed and opens on HP. Hopefully someone with later model systems than mine will chime in, just do not rip into changing parts yet.

 

[DavidC]

I really did not explain the LP and HP switches right and they both need to be closed for the clutch to activate. If the LP goes to low the switch opens and the clutch disengages, if the HP goes to high the switch opens and the clutch disengages. Clear as mud ?. So for a normal operation both switches need to be closed (continuity with an ohmmeter) on both.

 

[Jim W]

I have an 2008, at 85,000 miles my A/C failed. The compressor lock up and stop providing cool air. I had my local garage repair this and they ended up replacing the Compressor, A/C accumulator and recharged the system.

 

[HPSimpson]

Well sounds like you got a good compressor lasting 12 years that's pretty good.

 

[vrt93]

Ok, so I got a volt meter on the LP side switch and couldn't get continuity on any two pin combo (there's 3 pins for the switch). I'm just wondering why the LP side was building pressure with the compressor off?

 

[DavidC]

3 wires indicate to me you do not have a switch, instead it is a sensor probably tied into a computer. A switch was to easy. As I said earlier when the system is not running the pressure between High and Low will equalize. When the clutch engages and spins the compressor the low side will decrease. Unless some one with more knowledge of your system chimes in here you may have to find a reputable shop (sorry).

 

[Jim W]

Well sounds like you got a good compressor lasting 12 years that's pretty good.

When I posted I never gave it a thought as to what year I had the A/C system rebuilt! I did not get 12 years out of the A/C system before repair. It was more like 8 years. I had the repair work done in the Summer of 2015. Which is still pretty good in my opinion!

 

[cerberusiam]

The snowflake light and button is a momentary switch that tells the TIPM to close a relay and run the compressor. If the light is not coming and the compressor is not on, the control panel is probably bad. If the light is on, the compressor not running, and there is power to the compressor that is either as bad coil, bad TIPM relay, or bad ground.

FYI, the AC unit grounds back thru one of the battery ground post wires on the driver side. If that ground is inadequate showing high resistance the AC clutch will not engage even though the snowflake light is on and the TIPM is powering the relay and there is adequate voltage at the compressor.

 

[Tuesdak]

I'd eyeball the compressor clutch and then ohm check it's coil. If the clutch slips because (say it had too much oil on it or compressor locking up) it will blow an internal thermal fuse. A slipped clutch will look burnt.

The "sometimes it works" is a bad sign: loose electrical somewhere including the suggestions above. Grounds are a good place to start.

FWIW: The gauges indicate it at least has some charge in it: aka that ain't the problem. The pressures change as things heat up or cool with the engine off. Esp. If the compressor isn't running gauges only tell you there is R134a in the system... Note these systems only look at high side pressure to operate the fan (and maybe force recurc mode) otherwise: it doesn't care what the pressures are high/low/empty.

 

[vrt93]

Sorry to resurrect this, just managed to get some time to look at this this past weekend. So cerb, you're saying it might need a new TIPM? Ohm checked the coil and it's right at 4 Ohms, so I don't think it's a compressor issue. All the grounds seem fine and i'm not having any other issues that would suggest the TIPM is going bad, so my initial assumption would be a wiring issue on the harness between the TIPM and the compressor

 

[Ozymandias]

Well, you need a decent software that you can do an actuator test with Then you can switch on the compressor directly and see if it is commanded and runs - or not.
For sure you don't want to buy a TIPM just by guessing aren't you?

 

[rfitzgarrald]

Disclaimer: I know very little about A/C systems (enough to fix very basic problems) and I'm going off of logic here.

Rundown of the situation: A/c stopped blowing cold air recently. Fan comes on, but the snowflake light wont. Sometimes, if I leave it on, the light comes on and it will blow cold for a while before shutting off. I noticed the compressor isn't kicking on when the light is off (duhh). Today, after about an hour of driving, decided to hook some gauges up and see whats going on. Noticed that my LP side was at 120 with the ac turned all the way up and steadily climbing. HP was around 120-130.

Now I'm assuming the compressor isn't kicking on because its sensing that the LP side has adequate pressure (or at least isn't dropping below whatever threshold the sensor is set to read). This tells me that, logically, there must be a blockage somewhere in my LP line, either the compressor, evaporator, or dryer, and its preventing the LP side from building pressure. Seeing as my compressor will kick on, and works, I'm assuming I need to change either my dryer or my evaporator?

Is your fan clutch kicking in? When you first start the truck do you hear it “roar” if not you could have a bad fan clutch. There’s a pressure switch by the compressor that might be bad. Go to an a/c shop and they should be able to see what the hi pressure side is in relation to the lo side. If your clutch fan isn’t coming on the hi side will go above 350 and higher if it keeps climbing you run the risk of blowing the seals in the compressor and loss of refrigerant.

 

[Jim W]

I would not just throw parts at any issues that you have, if you do not do the proper testing to verify the failure. When you throw parts base on an internet forum responses you are just wasting money. Either go to a competent AC shop or buy a manual on AC repair. Then purchase the proper tooling and instruments to do the trouble shooting to find the fail component, in the long run you will be money ahead.

 

[rfitzgarrald]

Thanks for the response.
I agree with you in not just “willy-nilly” throwing parts at something without going to a shop. The reason why I said what I said was my a/c compressor went out. Had it replaced along with the pressure switch. 11 1/2mos later (just before the warranty on the compressor expired) a/c went out again. I sprung for a new pressure switch again, had it installed along with new compressor o-rings & seals. The technician read the gauges and it helped but the hi side was still reading somewhat higher than normal. Without going into troubleshooting the electrical signal, of which I told him not to, he suggested that the fan clutch could be the culprit. Having bought the truck used (113k+ mi then, now with 178k+) I figured that was a pretty good suggestion and a pain in the ass to replace (damn 1pc radiator shroud). A/C has been blowing ice cold ever since. (18mos & counting)