A/C Diagnostic help

[Pstyckiewicz]

Thank you!

 

[Pstyckiewicz]

Tested some more wires today. Not sure how many volts I’m suppose to get but figured 24v. Got around 14+ until I got to front Evan temp switch. Got nothing on the 438 wire on other side. By passed it and then got nothing on the other side of the low pressure switch 436C. I notice I wouldn’t get any power if the water valve was plugged.

 

[Mogman]

You have a bad connection in the other direction, you should see 24V.
You need to start looking at circuit 435, does the high and low speed work on the front evap?
You can also look at 435 C/D trying both the low and high fan position.

 

[Pstyckiewicz]

The high and low fan speed work. I also have power to the right rear cond. fan if unplugged from dryer and jumped together.

 

[Mogman]

That makes no sense if you are actually not seeing 24V at the temp switch

 

[Mogman]

Until you actually need high blower on the evap (filling of coolant) do all testing with the blower on low, this will bypass any possible issue with the diode in the fan circuit.
If you can get the cond fans to run by jumping the low pressure switch then the only things left in the comp. clutch circuit is the high pressure switch, comp. clutch and the wiring between them.

 

[Mogman]

BTW the labels low and high speed on wires 399 and 400 behind the blower switch are backwards, the wire 400 out of the fan switch is low speed.....
400 goes to the low speed resistor, 399 bypasses the resistor for high speed at least on this schematic.

 

[Pstyckiewicz]

Awesome info! I’ll give that a try. Thanks for all the help!

 

[Pstyckiewicz]

Thinking my cheap multimeter is not working right. The thing is all over the place. I tried the low speed on the fan kinda got the same results as before. I plugged in the water valve (435B) and lose power to the (435D) . Seems like the water heater valve is connected in some sort of way.

Multimeter
Harbor Freight set to:
DCV on 20 setting and tried 200 setting.
20 -would get me a 1 symbol sometimes like it too much or a low number. Like 8
200 - would go up to 190 and some times go to (-) negative number. This is me grounding it to mostly the ground behind instrument cluster, negative bus bar in battery box, or metal part of the motor.

Going to get a better multimeter. But it seems like there is more going on than I can understand with the wiring diagram can show. Like why if one thing is plugged in I lose power to somthing else that should have power.

oh and it should be known that I have very little experience with electrical stuff but can figure out most things after awhile haha. Mostly YouTubing how to work on things.

 

[Mogman]

Does your meter work when you measure the battery voltage?
Also you need to get ground for the neg lead from the engine block or battery, never from the body.
You may have a bad A/C switch

 

[Mogman]

Also at this point explain what you are trying to do, get the cond fans to run, get the comp. to kick in or something else.

 

[Pstyckiewicz]

When I connect it to the - buss and + buss in the battery box I get 190.00ish this is set on DCV 200. When set on DCV 20 the numbers go up and then get a number 1 as a it’s over the limit of what it can read. I get the moving from 20 to 200 just moves the decimal. The tester some times not connected is still reading high voltages. Then I connect the red and black point of the tester together and that brings it bad 0. Probably user error but could be a cheap tester.

 

[Mogman]

When I connect it to the - buss and + buss in the battery box I get 190.00ish this is set on DCV 200. When set on DCV 20 the numbers go up and then get a number 1 as a it’s over the limit of what it can read. I get the moving from 20 to 200 just moves the decimal. The tester some times not connected is still reading high voltages. Then I connect the red and black point of the tester together and that brings it bad 0. Probably user error but could be a cheap tester.

I would say that meter is toast.

 

[Pstyckiewicz]

What I’m trying to do is follow the origin of the power and see where it goes. If I find something that appears to not work I would bypass it. I got the clutch to engage and compressor to work for a short time by bypassing all of it by running a wire from batter to it. It turned on without any weird noises. Started to build some pressure. It seems everything works but something is stopping the power from turning everything on. The question is, is it acting as it should for example pressure sensor stopping it from turning on. I don’t believe so.

 

[Pstyckiewicz]

This was from the other day when I got the compressor to turn on for a second.

 

[Dieselmeister]

Looking at the gauges, that looks low on refrigerant, if the compressor is running. You still have an electrical problem though. Instead of a meter, I would rig up a 24 volt lightbulb with long wires on it (solder the wires to the bulb if you don't have a socket) and use that for trouble shooting. A meter will read 24 volts through a bad / corroded connection, with no load on it, giving you a false indication. A light bulb provides enough load to "overload" the bad connection. A bright bulb = good connection. A dim or off bulb = problem. Use the wiring schematic, and start with one wire, and work it through from one end to the other. Then start on the next wire. It may be a bowl of spaghetti to a non-electrical person, but remember, these spaghetti have a beginning and end somewhere. Take your time, and don't let a lack of knowledge intimidate you. Remember it's not working now. You can only make it better, and learn from it.

 

[Pstyckiewicz]

Ok got a new multimeter. What a difference. The A/C switch on the dash appears to not work. Jumped 435A to 435E and bypassed the switch. Got power all the way to the low pressure switch. Nothing past it. Jumped it and every thing turned on.
So it looks like the A/C switch is bad and possible the low pressure switch.
Put some refrigerant in and hooked up the low pressure wires to see if the adding some stuff to the system would get the switch to work. It didn’t. ( picture attached of pressure after adding refrigerant).

 

[Pstyckiewicz]

Also the heater core is really hot in the front Evap assembly. I think the water valve is stuck open. Tried to clamp it off with some vise grips but it still seemed hot . Probably didn’t clamp good enough.
Is the valve held closed when the power to the A/C is on? Seems strange

And one last thing. Got the front evap cooling down and started to form a lake in the truck from the condensation. Is there a drain hose that hooks up a certain way?

 

[Mogman]

Also the heater core is really hot in the front Evap assembly. I think the water valve is stuck open. Tried to clamp it off with some vise grips but it still seemed hot . Probably didn’t clamp good enough.
Is the valve held closed when the power to the A/C is on? Seems strange

And one last thing. Got the front evap cooling down and started to form a lake in the truck from the condensation. Is there a drain hose that hooks up a certain way?

Glad you found the bad switch, that was starting to look suspect, yes the valve is closed (powered) in AC mode, failure of this valve is very common, you can force it closed, many replace it with a manually controlled valve and just switch it depending on the season.
Yes there is a drain hose that connects to a nipple on the bottom of the evap unit, unfortunately these are sometimes broken off

 

[Mogman]

Ok got a new multimeter. What a difference. The A/C switch on the dash appears to not work. Jumped 435A to 435E and bypassed the switch. Got power all the way to the low pressure switch. Nothing past it. Jumped it and every thing turned on.
So it looks like the A/C switch is bad and possible the low pressure switch.
Put some refrigerant in and hooked up the low pressure wires to see if the adding some stuff to the system would get the switch to work. It didn’t. ( picture attached of pressure after adding refrigerant).

You still look a little low, there are many charts out there for the R-134A that show the desired pressures depending on ambient temperature, these are with the fan on high and at 1800-2000RPM
But the low pressure switch should be allowing the compressor come on although it may be short cycling.