every spring, my AC works great, but then as it gets hotter out it eventually stops turning on. there is plenty of freon, and I've had a couple places look over the system. one place said there are no leaks and that it's just a matter of the compressor not turning on all the time. when it does, it's ice cold, but it's just picky. seems to work when it rains, so I'm not sure what that's about.

I'd like to run a switch to power the compressor manually. I'm ok with electronics as long as I know where to start looking. has anyone done this in their truck? where would I look for the power wire for the compressor?

EDIT:
I forgot to say that this is not a relay issue. I've swapped for different relays, new ones, etc. also, the light doesn't blink ever, it stays on. the compressor just seems to decide when and when not to turn on.


J.

Don't do that. Find the route cause of the issue. AC systems have high pressure and cycling switches for a reason. You will not be able to properly cycle your AC compressor on and off with a switch. If you need help diagnosing the issue I can forward a troubleshooting flow chart.. Assuming you have and can operate a volt meter.

if you do, that would be great. I had one of the shops tell me it was the electric HVAC panel that was the issue, but I don't think they went in and tested stuff. it seems like there's some short somewhere that causes it to not work some of the time.

J.

You may have already ruled this out, but one thing you can try is replacing, swapping, or tapping the A/C relay. From what I can tell, some of the factory relays they used are prone to getting stuck and causing problems

This happened to me, where the A/C light would randomly start blinking and the compressor wouldn't kick on. I was in a hurry in the summer and didn't have time to grab a new relay, so just gave it a few good taps against the hood to knock the arm loose and it's been fine since

yes, I should have prefaced with this and I'll add it to my first post. I did try the relay and it's not the issue. and the light does not blink, it stays on. the compressor just chooses when and when not to turn on.

J.

What you are describing can be a few things. Pressure switches going bad, faulty wiring (including the HVAC module itself), a failing compressor clutch, or even a low or high AC charge, or the thermistor is shuting the system down so it doesn't freeze the evaporator (a failing thermistor will shut it down prematurely)



I believe a thermistor is probably you issue. But that's just a guess. You need to test stuff.

I am trying to pull a flow chart for you on identifix but it's being a pain in the ass to get over to here as it won't allow a PDF. I attached the PDF as a zip file. Let me know if you need more help.

Attached Images

05_21qj9__73z__ci__ha4_.pdf (27.0 KB, 71 views)

I'd bet the thermistor is your problem. I had to replace mine as soon as I bought my runner. It's a pain to change but not costly if you do it yourself. You can actually buy the thermistor at the dealer for about $15 if I remember correctly.

Can someone help me understand the circuit?

I’ve got a blinking ac light and no cold air. Jumping the relay with a paper clip will power it on. Replacing the relay with the fog light and a new one didn’t do anything.

I just had the compressor replaced by a shop and they told me the low pressure of 35 for refrigerant is normal based on our temp

If I disconnect the harness into the ac pressure switch the ac light in my car will stay on but will not blow cold air. If I plug that harness back in the light starts blinking again. If i try to bypass this switch with a paper clip again nothing and the ac light blinks

Checking the voltage on the switch harness I get about 13v with the ac button pushed.

Anyone have thoughts on where the issue is? If high ( or low) pressure from the switch shuts off the compressor and normally it runs with out the switch I’d think I’d be getting cold air. If the switch provides power to the compressor as long as the pressure is normal then I’d think I’d need to jump the circuit to get it to work and the ac light should be blinking when the harness is out

at $12 for the part, I'll replace it and see if that helps.

J.

As far as the pressure switches. They are necessary to complete the circuit. If I recall correctly, the ECM provides a necessary ground to the relay. To do that it has to see several things. First, that the request is made, (a/c switch turned on), the pressure is correct, (not too high or low), and the temperature inside the evaporator is correct, (the thermistor breaks the circuit when it gets cold enough... to prevent freeze up). If you want to see if the pressure switch is where it's breaking the circuit, you have to jump across the two terminals on the harness to the switch, (paper clip etc.). But remember, if it comes on when you do that, it doesn't necessarily mean the switch is faulty. The pressure could be off and the switch is just doing its job. There may be more but that's all I can come up with from memory. Hope that helps some.

Edit to add: I forgot about the revolution sensor. If the compressor is trying to lock up, or if the revolution sensor is going bad the ECM will turn off the A/C to prevent it from burning up the belt and totally disabling the vehicle. And it definitely will make the light blink.

ok, quick update:

replaced the thermister. no dice...it was a PITA to get it out and it didn't change anything.

however, it's been raining the last few days and, of course, the AC now is running just fine. again, it seems to be a humidity thing. what can I check next? could it be the sensor under the steering wheel that works when it's damp outside? I find it really strange that it works just fine when it's been raining. almost like some wiring somewhere is completed when it gets humid enough...a motherboard somewhere? the control panel itself?

J.

I would t do it but if you want to jump it, Scotty to the rescue

Doing This Will Bypass Your Car's Computer and Give You Freezing Cold AC - YouTube

Captsolo and FordF150 get banned and you take over shilling Kilmer? What's next tell us about your All American status in 1945 and ur boat in the Bahamas?

Jokes kids these are just jokes

Miss that guy

it stopped raining finally, and like clockwork the AC shut off two days later.

I've jump-tested all the things and as far as I can tell, the relay is not getting the input correctly from the dash. replacing the relay with any others doesn't work. but when I take the relay out and jump it, the compressor runs just fine. I replaced the control panel with a working used one and no dice. the guy at the yard where I bought the control panel said there's an AC computer behind the panel that I should check next. so who knows.

for my 12-hour road trip tomorrow I'm just wiring a switch to turn it on and off manually. I don't want my kids suffering for 12 hours, haha.

if anyone has any other ideas, please let me know.

J.

ok, reviving this post with a new question: what causes the compressor to cycle?

I coulnd't figure out why the compressor wasn't running. I tried replacing the AC amplifier and that never helped. my AC light is solid, but nothing happens. so I ran a switch straight to replace the relay and spent all last summer just turning the compressor on and off manually. but that also meant that it doesn't cycle, I have to turn it off manually after a little while or it would get too cold and freeze up.

so, what controls the cycling of the compressor? is it the AC amplifier? or is the something after the relay?

J.