fixing the AC

[roadgrime]

anyone good at reading the wiring diagram for the 79 cherokee? I can find the two switches that are located on the ac panel. i have 12 volts going into the unit and then it seems like it should hit both switches. however the fan doesnt come on and if i follow the blue wire to the fuse box i dont have voltage going in. Im not sure if its a ground or 12 volt feed to the ac unit from the compressor or if its a ground feed from the controll unit to the compressor through the firewall.

[ June 05, 2004, 08:36 AM: Message edited by: roadgrime ]

[Chevelleguy]

The wires are all 12v, not grounds. The series goes: Fuse box, temp switch, fan switch,(through firewall) high press switch, compressor. Voltage flows from fuse box to compressor. Compressor is grounded and the end of the circut.

[ February 24, 2004, 07:23 PM: Message edited by: chevelleguy ]

[g503]

http://209.238.200.129/gw/elec/GW_wiring.html

[roadgrime]

ok I have verified the brown wire connected to the ac compressor is shorted to ground. is this normal? Also the blue wire running into the controll unit is shorted to ground until i disconnect it from the fuse box (top right corner single wire connection on fuse box)

[roadgrime]

I have the wiring diagram. the only wire i can find on the diagram is the brown wire to the compressor (50 brown 16) on the drawing going to the compressor in A4

[Chevelleguy]

A short to ground is not normal. The only place the circut should be grounded is when it terminates at the compressor.

[Chevelleguy]

The blower resistor is in the vent housing above your left knee. Make sure it is pugged in and that none of the wires are worn through. When you say that it is shorted to ground do you mean it is blowing fuses?

[roadgrime]

no not blowing any fuses that i can find. i took the multimeter and with the connector plugged into the compressor i checked continuity to ground and it showed to be shorted to ground

[Chevelleguy]

The compressor uses a coil that is grounded so all you have proven is that the circut is not open and that is o.k.

[roadgrime]

not sure i understand that cheve... if its supposed to have 12 volts at some point when operating. it should read an open to ground as i understand it.

[roadgrime]

welp im gonna try and follow the 12 volts through the two rotary switched and see if i can reverse engineer this thing. if anyone knows where on the wiring digram the switches are let me know.

since i cant read the panel what do the left and right knobs control.

[g503]

http://209.238.200.129/gw/elec/GW_wiring.html

[g503]

one switch is the fan speed the other is a
thermostat ,that you turn up and down to set the temp

[roadgrime]

g503. thanks for the link but as i mention above i already have the wiring diagrams. The onlything ac related that i see shown is the compressor wire

[Chevelleguy]

The switch on the left is OFF(far left) and fan speeds. The one on the right is OFF(far left) and colder(far right). The A/C circut is very simple. You have 12v power and you have ground. In the middle you have 3 switches and a clutch coil. If you have and 'open' in the system, then it won't work because the circut is not complete. If you have a 'short to ground' it won't work because the voltage is going directly to ground and not through the components. Start at the fuse box (because this is your source) and work your way to the compressor (this is the end of circut). Fuse box, fan switch, temp. switch, high pressure switch(under hood on passenger side fender in the high pressure line) then the compressor. It really is very simple. Good luck.

[roadgrime]

ok im gonna type this out so others can tell me i am smoking crack. the fuse box has 12v(red wire) going to the reostat(fan switch. these are both 12 v.here it splits off. 12 v(black wire) goes through the reostat which then feed the blower motor which gets its ground via a ground wire on the passenger side of the dash. the reostat mentioned above drops the voltage which in turns varies the speed to the blower motor.

Back to where it splits off mentioned above on the reostat there is a second red wire...i think 12 volts going to the temp control. also on the temp control is a a blue wire(feed to the compressor via the fuse box. and a solid wire which runs down to the condensor nect to the blower motor. this i think is a temp sensor but i am not positive.

the blue wire i just mentioned turns to the brown wire (50 brown 16 on the wiring diagram) which i would assume by chevelleguys comments above then goes to the high preasure switch and then on to the compressor.

is that about correct?

is there a way to check the high preasure switch? and also i dont see a site glass on the compressor to check for bubbles. its a 79 cherokee if that helps

[Chevelleguy]

The sight glass is in the high pressure line next to the high press. switch but may have been removed by a previous owner if line was ever replaced or rebuilt. It is call a blower resistor not a reostat and with an ohm meter you can check the high press. switch for continuity. It opens if the pressure gets too high. With the A/C on you should have 12v in and out of each component, if you don't, that is the bad part.

[roadgrime]

ok last stupid question i hope... is ther an alternate location for the preasure switch?

from the compressor the top line is 1 inch id and goes back to the firewall into the condenser

the bottom line is 3/4 id and goes forward to the front of the radiator to the evaporator?
out of the evaporator is a 1/2 id hard line which routes up to the passenger wheel well where i finally found the sight glass in the middle of a coupling. however there is not a switch or wire in or around it. and nothing that looks like it should have wires. this 1/2 id hard line then continues back to the firewall. and into the condensor.

please note i may have the condensor and evaporator backward as my book is currently awol

[roadgrime]

sorry yes i have them backwards. in side the cab isthe evaporator. in front of the radiator is the condensor and receiver. books are a wonderfull thing. however even though it shows the entire system it doesnt show the preasure switch.

[roadgrime]

welp i am gonna get back to this again tonight. i picked up a couple extra blower resistors from the junk yard tonight since mine fell apart last night. and i could not find the preasure switch on mine nor on any in the junk yard on the passenger wheel well

[TexasJ10]

I'm not sure what year the pressure switch started showing up, and it is very possible that yours was never equiped with it. BTW, frequently this switch is actually a low pressure switch. Since the system circulates oil with the refrigerant, the switch was designed to keep the compressor from running without adequate oil flow when the refrigerant leaks out.

I think you have done a good job of describing your system, but I don;t see where you have told use whether you actually have 12 volts at the fuse box connection for the red wire and whether you have 12 volts at the blue wire after you remove it from the fuse box connection. I believe that both the fan switch and teh temp switch need to be turned on to see if you have 12 volts at the blue wire. If you do, the problem is in the engine compartment. IF you don;t you can start tracing it down to the fan swith and temp control.

[roadgrime]

ok well I replaced the blower resistor and that got most of the stuff working. still didnt have 12v to the compressor. so i started following wires. found a wire that was frayed and shorted to ground the brown one to the compressor. at least now the compressor kicks on. i see some bubles in the sight glass but not alot. cant tell if its gonna get cold or not since i can only idle in the garage.

[roadgrime]

hey texas yea. i had 12 at the red wire. but then it was gone in the box. once i got it apart i figure out that the blower resistor was shot. I found several in the junk yard and one was out enough where i could finally see where stuff was supposed to go. I also found a break in the blue wire as well so both the brown and the blue were screwed up. those are fixed now and allow the compressor to kick on. doesnt feel like fridgid air but then its only 60 in the garage

[TexasJ10]

Good work. You went about solving a frustrating problem correctly. Has your system been converted to 134a refrigerant? If it has, you will see bubbles even though it is charged correctly. Is your compressor kicking on and off on it's own? Since you don't have a pressure switch, this likey means it is getting evaporator temp sensor readings that are low enough that it is sending a signal to the compressor to disengage. That would be a good sign.

[roadgrime]

I dont think it has been converted. I dont see any stickers nor do i see signs of work being done to the system.

also with it at idle it did not kick on and off except via the switch

[TexasJ10]

Are you seeing bubbles when the clutch first engages or are you seeing them all the time? One of the problems with site glasses are that it is very difficult to see whether you are looking at a tube full of fluid, or a tube with no fluid at all. If there are bubbles all the time when the compresor is engaged, you will probably need to add a little r12 or freeze 12 to top it up.

[roadgrime]

looks like they are their all the time. tiny and few. actually watching them it seems like they are the same bubles.not bubles moving through the line. but it does apear there is fluid in the line. also i notice the large diameter line from the compressor warms up after just a few minutes.

can r12 or freeze 12 still be gotten?

[ February 26, 2004, 09:09 PM: Message edited by: roadgrime ]

[TexasJ10]

You can take an online test for $20 and be certified to buy r12. You can still find it behind that counter at some autoparts stores. I saw a case of freeze 12 at the PEP Boys here. I am not sure whether you have to be certified or not to purchase it. I think you might be able to get freeze 12 on line too. If you want I can give you the online testing site. The fact that your large hose is getting warm is good. The heat is being removed from the air and carried to the compressor to be pressurized and moved to the condensor to cool back into a liquid.

[roadgrime]

yea i wouldnt mind having the site. im prob gonna have to wait for a warm day and see if it blows cooler. but i think im getting close

[Chevelleguy]

Don't put Freeze 12 in, it is 80% 134A and cannot be mixed with R12. I know it has been done, but the long term effects wont be good. If you read the can it will tell you to evacuate the system the recharge.

[TexasJ10]

chevelleguy you make a good point about the contents in freeze 12. I have never understood it, but my brother in law has used it for years to top up his car with no apparent detremental effects yet. For some reason this stuff coexists with r12. I still top off with r12 for the reasons you mentioned, but man that stuff is getting expensive.

The link for the certification is
http://www.epatest.com/e_609cert.html

$19.95, 45 minutes of studying their online study guide, and 25 questions on an online test. You only need to get 21 right. They give you a temporary card upon scoring your test with a permanent card sent by mail. Very easy

[Chevelleguy]

That is why I just convert everything I own to 134a when needed. Only $3.99 a can with my account at O'Reilley.

[roadgrime]

welp now that its warmed up after having went though everything above. its just hot air blowing. I checked the valve on the wheel well and i can see the fluid flowing through it but it doesnt look like its full.

any thoughts?

[Chevelleguy]

Have you put a set of gauges on it? What are your pressure readings? How many cans did you put in?

[roadgrime]

no I havent put a set of guages on it yet (dont own a pair yet) is it worth it for me to get a set of guages even though i dont have any freon to put in it and dont know that any shops around here will have any...

[Chevelleguy]

You (I) have to know the pressures inorder to diagnose the problem. Anyone with a license can still buy R12 and all the auto parts stores carry it.

[roadgrime]

ok well let me see about getting some reading and i will post it back here when im done.