I have a question about my ac. I have a 99 k1500 5.7, we replaced the compressor and evap core but the fan only works on high, the ac button doesnt light up, and the compressor doesnt come on. Is this a problem with the control box in the dash? I tried shorting the low pressure switch and the compressor still wont come on. What else can I try. Just checked no power at plug to clutch. Could I replace the plug head or would it have to be the whole wire?

Josh Marxen: Are you getting power on the backside of the plug just not through it? if so you can replace the plug; where the wires connect to the spades might be bad. If you dont have power at the backside coming into the plug you have to go back farther.

Trisha Garcia: Its a bunch of wires together that then go to separate places,everything else works so Im assuming theres power on the other end.

Trisha Garcia: Im going to try and replace the plug and if that doesnt work then I guess Im bringing it to a shop the rest would be beyond me. Replacing the evap core was a test of patience and will on its own. Im about ready to call it quits on the a/c.

Josh Marxen: The fan only working on High means the blower motor resistor is probably bad and maybe why the AC wont turn on. I dont remember exactly how these are wired on the newer model chevys but have replaced a lot on dodges. On the wires one is power one tells it to turn on one tells it to cycle… Unless the plug is burnt or damaged its not likely the problem. More than likely when the old electric clutch went bad it took out another component and Im assuming you already checked and repaired any bad fuses

Josh Marxen: There is also the relay

Trisha Garcia: The fuses are good but what else should I look for which relays? Wheres the blower motor resistor located? In the dash with the ac housing? Or would changing the control box fix it?

Josh Marxen: There should be a relay in the box under the hood, just switch it with another relay see if problem moves. the resistor is near the blower motor may have to remove the glove box. Much cheaper than control box and most likely cause of blower motor problem so thats where I would go first. They are not hard to change. IDK for sure that will fix the AC but Im 95% thats will need replaced to fix the fan

Trisha Garcia: Alright I just looked up how to change it out, I wish I did it when I had the whole dash out.

Josh Marxen: A lot of components are tied together so it maybe not letting the AC turn on.

Trisha Garcia: I hope so the control is 200$ plus I thinking I may not have needed to even replace the compressor 😰

Trisha Garcia: The first thing Im going to do is check that plug well though, I know Ill need the resistor anyway for the fan so Ill do that too but I need to figure out why theres no power to the plug.

Josh Marxen: On a 99 it probably didnt hurt. If you have a meter test where the wires come into the back. Its tight but it will let you know if power is getting to it. Its very rare for a control box to go bad unless someone has messed with the wiring installing stereo or other. The switch not lighting up tells me that its not getting the ok from the computer. My 2000 will light up even though the compressor is dead

Trisha Garcia: The computer was replaced last year but its been sitting, Im just hoping its an easy fix weve rebuilt this entire truck just for the air not to work 😡

Josh Marxen: If you had to replace the computer its possible someone hooked up battery jumper cables backwards or worse the truck was in a flood which means chasing rotting connections. Try the relay first resistor second and then have a pro take a look before the control panel. Good luck 🙂

Trisha Garcia: Thanks, anything is possible it was a mudding truck so it needed a whole new underside and dint have breaks on the back tires.

Ronald Johnson Sr: There is a fan rectifier that controls the fan speeds if it is blown out you will only have high speed

Trisha Garcia: For the fan it was a fuse on the side of the dash, thats fixed so i hve all my speeds but the compressor clutch still wont kick on

Trisha Garcia: Im thinking its the low pressure switch. Wont even start the compressor jumpered. Im also going to get the sensor and accumulator.

Ronald Johnson Sr: Did you change the drier,and evacuated properly, if there is any air in the system it wont work, if there is too much freon compressor wont work, and if there is not enough freon it wont work

Trisha Garcia: The drier is all I have left to change. The lines were vacuumed and everything at its proper level

Ronald Johnson Sr: You jumped compressor clutch and it wouldnt pull in ? Then clutch is bad

Trisha Garcia: I jumped the compressor clutch and it works. For some reason something isnt letting it turn on.

Amie Plaster: Trisha Garcia you are like my superhero. I wish I knew half the stuff you know. Go ahead girl

Trisha Garcia: Haha thanks! My parents are engineers and my brothers and both brothers in law are mechanics. That made for some interesting weekends.On a side note I have now replaced literally everything but the pressure switches. From fuses, to relays, down to the orifice tube and its still not working. Im going switch hunting today and if that doesnt work Im at a complete loss.

Amie Plaster: Good luck 👍

Trisha Garcia: Thanks!

Bruce Martin: Im not sure about your model, but in general, youve put power to the compressor clutch and it engages, your interior fan speed is now working cortectly, all gas levels are correct, things that may prevent operation, fault on outside temperature sender or circuit, high presure switch or cicuit fault, power supply from control unit for aircon, if there was dirt in the air con system when the new compressor was fitted the new unit may be damaged, when gassing a aircon the compressor must work to suck the remaining gas in the charge lines through the low presure side, a lot of possibilitys,

Ronald Johnson Sr: If compressor is too low on freon it will not pull freon,you should re-reclaim freon ,pull a holding vacuum of 29.9 in vacuum if it does not hold a vacuum you have a leak and will not work

Ronald Johnson Sr: If it does hold measure in the correct amount do not add

Bruce Martin: First need to test if you have power to your compressor and trace it back from there, checking both positive and negative lines, also testing for any stored faults in your on board control units, some aircon systems depend on battery voltage and coolant temperature, good luck.

Trisha Garcia: Im about to throw in the towel and bring it to a mechanic

Trisha Garcia: Well I just found a cable that isnt plugged into anything…

Bruce Martin: Hahaha, thats always fun, where does it belong and what does it do??? 😂

Trisha Garcia: Jokes on me guys that cable goes to the back of my compressor that my brother-in-law installed for me but I looked at the back of it he didnt take the c ring out or put the old connector on so the switch wasnt plugged into the back of the compressor

Trisha Garcia: Probably why it isnt coming on 😂😂

Ronald Johnson Sr: Lets hope, good luck

Bruce Martin: I hope the system was flushed before the new compressor was fitted, there may be particles that the old faulty compressor left in the system that may circulate back into the new unit. Plus the aircon had to be working at the time of charging with gas to ensure the correct content.

Trisha Garcia: I called him he said the sensor was broken on the old one and thought he told me/ my husband.

Trisha Garcia: Just getting back with a new sensor. So moment of truth soon

Trisha Garcia: I wanted to get that on without removing the compressor but it looks like I have to. Too much in my way to be able to replace the c ring over the sensor.

Trisha Garcia: We have ac 👐

Trisha Garcia: Now the compressor wont cycle its always on while the ac is on.. 😡

Bruce Martin: Too much or too little gas, possible particles in system circulated into the new compressor, was it flushed before fitting the new unit ?

Trisha Garcia: Yes

Bruce Martin: Check all fuses again, was working and now its not.

Trisha Garcia: The accumulator is sweating but the clutch isnt cycling. Now I only hve high fan speed again too

Bruce Martin: Sounds like an Incorrect fuse or interior fan resistor problem.

Trisha Garcia: Im going to replace the blower resistor tomorrow.

Ronald Johnson Sr: If its hi-sp fan your clutch should not cycle at idle,

Trisha Garcia: It has high and then one down barely blows.

Bruce Martin: Interesting, that comes from product knowledge. But the fan only working on high speed again?

Trisha Garcia: It kept blowing a fuse before but now the fuel is fine so Im guessing its the blower resistor.

Trisha Garcia: Fuse*

Bruce Martin: Sounds like the next logical step👍

Trisha Garcia: Why is it such a pain in the Arse

Bruce Martin: Hahaha, thats the job, the joy and pride comes after fixing. Good luck.

Bruce Martin: So, what happend with you aircon?

Trisha Garcia: It works but for some reason wont blow very cold until about 65mph, and when you stop it gets hot.

Bruce Martin: Have it regassed, low pressure sold be around 2 bar, high presure around 9 bar. Rule is the lower the low presure, the colder it makes, expansion valve or restrict or might be faulty.

Trisha Garcia: Thatd be the 4th time. I may take it to a shop and have them charge it.

Bruce Martin: What test have they done, any leaks?

Trisha Garcia: No leaks but up until now weve done all the work ourselves.

Bruce Martin:

Bruce Martin: Gauges on aircon filling macine must look like this while aircon is on.

Trisha Garcia: Ill borrow them from Brother in law later today and check it

Bruce Martin: He must do it for you, gas gets lost in the lines.

Trisha Garcia: Hes the one thts been filling it for us.

Trisha Garcia: Since hes the one with the setup. If its not that what else could it be? Also new blower motor resistor and still only works on high, where the heater and evap core are also gets quite hot, I put my purse down there and picked it up and it was quite warm.

Bruce Martin: Fan switch

Trisha Garcia: This is no beyond my level lol, where is the fan switch?

Trisha Garcia: Or do you mean the one on the control panel?

Bruce Martin: Yes or the control panel itself, as for getting cold, dont know if your system works with an expansion valve or a restrict or that could be dirty

Bruce Martin: Restrictor

Trisha Garcia: Weve put brand new everything except switches. Sensors and all are parts are new. AccumulatorLow pressure sensorCompressor/clutchSensor on the back of compressorEvap coreBlower motor resistorOrifice tube… more I cant think of those are the ones I bought and most importantly installed so I remember them lol

Trisha Garcia: Even new relays and fuses

Bruce Martin: Talk to your brother in law about what Ive suggested, first need to see gauge readings, not always cheaper to do it yourself, take to agents for diagnose and quote?

Trisha Garcia: Either way the truck is a 99 and it looks like nothing has ever been replaced. So it good to replace the system now we just need it to work 😂The local shop I trust would charge about 40 to check it out.

Trisha Garcia: It was supposed to be a project truck and it certainly has been. 😧

Trisha Garcia: Before

Trisha Garcia: After, the ac is all we have left. The entire underside, tranny, motor, all new/or rebuilt.

Bruce Martin: Very nice, awsome. Well done

Trisha Garcia: Thank you, The ac works well enough for me at this point. We have a trip in a week we have to use a truck for so itd be nice to have it ice cold in Louisiana but Ill live if not.

Trisha Garcia: I may just have to put the ac on the back burner until we get bck. Ill bring I to the shop and see what they say

Trisha Garcia: Ok now my heater is getting hot in the housing unit under the dash while the ac is on…wtf… I give. Its going in the shop this weekend. Thanks to everyone for the help!

Bruce Martin: Possibly an electrical problem with AC control panel, good call to take it to shop👍