Tn75s air conditioning relay

[jammer48]

I am trying to bypass the clutch relay on the TN75S but I can't find the relay specific to the clutch on the compressor so I can activate it to recharge a completely drained system. Anyone know where it is located or how can I activate the compressor clutch since it has no freon in the system?

 

[Jerry/MT]

If it's anything like my NH TD95D, it's located on the evaporator which is above the headliner in the cab. I just had it replaced.

 

[nyone]

Never needed to located the compressor relay for a completely drained system. Did it drain out by its self? If so just add refridgerant until it kicks on. If you opened the system you should pull a vacuum or the system wont work properly.

 

[jammer48]

ok so i did pull a vacuum and it has a slow leak. I have now pulled the headliner after i put some dye in the system and I can't find the leak to save my life. I know it's a slow leak. I put two can's in about 18oz's and got the low side up to about 29psi put still no cool air. The High side was up to about the same pressure. I should have at least 150psi on the high side. I'm thinking the pressure switch/relay/valve might be stuck or at least the problem..... the compressor and clutch are working cause both cans got cool to the touch. It won't take anymore freon so I'm not sure what to do next.

 

[LouNY]

With 2 cans added in the low pressure switch should have made and ran the compressor. If you added two cans and had 29 psi on both the low and high side the compressor had never kicked on. It just equalized in the system. The cans will get cold anytime you dispense gas from the can as the liquid is vaporizing and cooling the can.

 

[Harry in Ky]

You claim the clutch and compressor are working, but your results don't confirm that. No matter how much refrigerant you add, if the high and low sides read the same pressure, you have an expansion valve problem (for openers). No offense intended, but as I see it you're in over your head on this one. No doubt there will be some well meaning suggestions coming, but you'd be better off calling in some qualified help. You already know you need help finding a leak. No one out here can do that for you.

 

[nyone]

Is the compressor turning?

 

[nyone]

No offense intended, but as I see it you're in over your head on this one.

Everyone that's willing to learn or do things them self is in over there head at some point. It's how you get out of it. If your going to smack every project with your check book you will never learn anything.

OP AC in this and vehicles arnt very hard to work on. We just need a few key questions awnsered.

 

[jammer48]

You claim the clutch and compressor are working, but your results don't confirm that. No matter how much refrigerant you add, if the high and low sides read the same pressure, you have an expansion valve problem (for openers). No offense intended, but as I see it you're in over your head on this one. No doubt there will be some well meaning suggestions coming, but you'd be better off calling in some qualified help. You already know you need help finding a leak. No one out here can do that for you.

Harry we all have to learn someway. And yes I suspected the expansion valve as well.

 

[jammer48]

Everyone that's willing to learn or do things them self is in over there head at some point. It's how you get out of it. If your going to smack every project with your check book you will never learn anything.

OP AC in this and vehicles arnt very hard to work on. We just need a few key questions awnsered.

Thank you!

 

[jammer48]

Everyone that's willing to learn or do things them self is in over there head at some point. It's how you get out of it. If your going to smack every project with your check book you will never learn anything.

OP AC in this and vehicles arnt very hard to work on. We just need a few key questions awnsered.

Is the compressor turning?

yes it is and the clutch was engaging

 

[jammer48]

With 2 cans added in the low pressure switch should have made and ran the compressor. If you added two cans and had 29 psi on both the low and high side the compressor had never kicked on. It just equalized in the system. The cans will get cold anytime you dispense gas from the can as the liquid is vaporizing and cooling the can.

Ok hmmm valid point so I suspect I have an obstruction? Perhaps the expansion valve? The compressor clutch definitely engaged.

 

[jammer48]

UPDATE So I read in one of the shop manuals I have for this tractor, that the expansion valve is located in the ceiling. LOL so I took the ceiling down and found all of my dye lying in a puddle of dirt. Today I am going to clean everything and attempt to pressurize the system and see if I get any results in terms of a leak.

There are two radiators in the ceiling. As I understand it one is for the heat and the other is the evaporator and the expansion valve is connected to the end of the evaporator.

 

[jammer48]

Everyone that's willing to learn or do things them self is in over there head at some point. It's how you get out of it. If your going to smack every project with your check book you will never learn anything.

OP AC in this and vehicles arnt very hard to work on. We just need a few key questions awnsered.

Thank you... my thoughts exactly.

 

[jammer48]

If it's anything like my NH TD95D, it's located on the evaporator which is above the headliner in the cab. I just had it replaced.

yes it is. I found it and a mess where a mouse had a nest in front of the evaporator

 

[jammer48]

2nd update!!!
I put freon in and touching the evaporator I had cold going in to touch and warm to touch coming out. Both sides of the drier were hot to touch and both sides of the condensor were hot to touch. guages showed 300 on the high side and 75 on the low side after freon. The static pressure, with the tractor off, was 100 on the low side and 200 on the high side. Finally, once the compressor clutch kicked on it never shut off or cycled. Any thoughts????

 

[LouNY]

High side seems abit high, maybe a touch to much freon.

From some of my literature;
"Before the vehicle is started, the static system pressure can be read.Pressure should be very nearly equal in both gauges. Actual pressure will depend on the type refrigerant and the ambient temperature and does not show if the system is properly charged. At 85 degrees Fahrenheit, R134A shows a pressure of around 90 pounds per square inch."


"Start the engine and turn on the air conditioner. Actual readings will vary according to ambient temperature. The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem."


"On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI. For instance, on a 90-degreeFahrenheit day, twice 90 is 180, plus 50 equals 230 PSI. This is not precise but close enough for the purposes of this article. Both pressures reading within these ranges means the system should produce a vent temperature in the mid, to low forties, with the engine idling."

 

[jammer48]

Thanks again Lou! I have that chart as well. I read that if looking for a restriction/obstruction you can actually feel the piping of your system and follow the temps and drops in temps for possible blockage. I am yet uncertain if I even have a blockage. I just came in because it was so hot outside. I will go back and take a staic opening pressure again and come back here with the readings.

 

[jammer48]

High side seems abit high, maybe a touch to much freon.
View attachment 3775644

From some of my literature;
"Before the vehicle is started, the static system pressure can be read.Pressure should be very nearly equal in both gauges. Actual pressure will depend on the type refrigerant and the ambient temperature and does not show if the system is properly charged. At 85 degrees Fahrenheit, R134A shows a pressure of around 90 pounds per square inch."


"Start the engine and turn on the air conditioner. Actual readings will vary according to ambient temperature. The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem."


"On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI. For instance, on a 90-degreeFahrenheit day, twice 90 is 180, plus 50 equals 230 PSI. This is not precise but close enough for the purposes of this article. Both pressures reading within these ranges means the system should produce a vent temperature in the mid, to low forties, with the engine idling."

"Start the engine and turn on the air conditioner. Actual readings will vary according to ambient temperature. The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem."

My reply: What could the problem be? When I obtain the start up reading should all of my gauges be open?

 

[jammer48]

High side seems abit high, maybe a touch to much freon.
View attachment 3775644

From some of my literature;
"Before the vehicle is started, the static system pressure can be read.Pressure should be very nearly equal in both gauges. Actual pressure will depend on the type refrigerant and the ambient temperature and does not show if the system is properly charged. At 85 degrees Fahrenheit, R134A shows a pressure of around 90 pounds per square inch."


"Start the engine and turn on the air conditioner. Actual readings will vary according to ambient temperature. The low-side should be near 30 PSI at 90 degrees Fahrenheit or less. Pressure that is too much lower or higher shows there is a problem."


"On a properly working system, high-side pressure will be about twice the ambient temperature, plus 50 PSI. For instance, on a 90-degreeFahrenheit day, twice 90 is 180, plus 50 equals 230 PSI. This is not precise but close enough for the purposes of this article. Both pressures reading within these ranges means the system should produce a vent temperature in the mid, to low forties, with the engine idling."

first ambien temp is 92 currently measured with a thermometer next to guages. Second, with tractor running and low side (blue) open at strader valve and High side (RED) closed I have the following readings. 51 on low side (which then dropped to 30) and the High side (red) was 290

Again with the tractor running I opened both manifold valves and the low side went to 175 and the Red High side dropped to 190.