AC help please

[jreask]

I have a 2000 SR5 with 175K . The ac blows cold but it is intermittent. The AC compressor clutch cycles on and off about every 30 seconds at idle and remains off for 15 seconds or so. Then it runs for 30-45 seconds before shutting off. When I hook up the manifold gauges the low side pressure is about 30 PSI. The high side pressure is close to 200 PSI. The compressor clutch kicks out and the low side pressure goes to 45 PSI and the high side drops to 160 PSI. There are no bubbles in the site glass. I don't know why the compressor is cycling so much. Help please. Thanks in advance.

 

[heat]

Any blockage in air flow (evap icing up)? Pressures look normal; all
the fault diagnoses in the factory SM involve high or low pressures.

 

[jgue467]

Mine cycles in about that range yet blows ice cubes (no bubbles either) so I think that type of cycling is normal for energy conservation.

 

[JRZEE2000TR4LTD]

I have a 2000 SR5 with 175K . The ac blows cold but it is intermittent. The AC compressor clutch cycles on and off about every 30 seconds at idle and remains off for 15 seconds or so. Then it runs for 30-45 seconds before shutting off. When I hook up the manifold gauges the low side pressure is about 30 PSI. The high side pressure is close to 200 PSI. The compressor clutch kicks out and the low side pressure goes to 45 PSI and the high side drops to 160 PSI. There are no bubbles in the site glass. I don't know why the compressor is cycling so much. Help please. Thanks in advance.

What's the ambient temp? The lower the ambient temp the more the clutch cycles as it cycles of the low pressure switch, which I believe cycles off around 25-30 psi. Ambient temp is linear with refrigerant temp which is linear with AC pressure. I would not focus on the clutch duty cycle. Also, how much time does it take for the pressures on the hi and low side to equalize when you turn off the AC?

You say the air coming from the vents isn't cold? When does it go warm?

 

[jreask]

What's the ambient temp? The lower the ambient temp the more the clutch cycles as it cycles of the low pressure switch, which I believe cycles off around 25-30 psi. Ambient temp is linear with refrigerant temp which is linear with AC pressure. I would not focus on the clutch duty cycle. Also, how much time does it take for the pressures on the hi and low side to equalize when you turn off the AC?

You say the air coming from the vents isn't cold? When does it go warm?

Thanks for the reply. The pressures on the high and low sides don't ever equalize I don't think. When I hook up the manifold with the engine not running, the low side pressure is 50 and the high side is about 100. I hooked the gauges up this afternoon and the low side was only at about 10-15 psi with engine running and the high side was close to 140. The temp from the vents raises about three degrees when the comp cycles off. I have a 2015 TEP and the comp cycles off about every ten seconds and stays off for about 7 seconds. I am assuming that this is normal with an ambient temp of 80 degrees. I am thinking the cycling is normal, like you posted.
Do you know the reason for the low side pressure showing so low? I am wondering about the calibration of my manifold gauges. They are not a cheap set but they are getting old, probably 12 years old. Let me know what you think about the low side pressure.

Thanks,
JR

 

[JRZEE2000TR4LTD]

Thanks for the reply. The pressures on the high and low sides don't ever equalize I don't think. When I hook up the manifold with the engine not running, the low side pressure is 50 and the high side is about 100. I hooked the gauges up this afternoon and the low side was only at about 10-15 psi with engine running and the high side was close to 140. The temp from the vents raises about three degrees when the comp cycles off. I have a 2015 TEP and the comp cycles off about every ten seconds and stays off for about 7 seconds. I am assuming that this is normal with an ambient temp of 80 degrees. I am thinking the cycling is normal, like you posted.
Do you know the reason for the low side pressure showing so low? I am wondering about the calibration of my manifold gauges. They are not a cheap set but they are getting old, probably 12 years old. Let me know what you think about the low side pressure.

Thanks,
JR

Really? they never equalize? Are you sure the ac system isn't running? I'm kinda doubting your gauge accuracy. What do they read with nothing hooked up? Do they read zero? Switch the hoses on the manifold set without the ac running and see if you have similar readings. Low side gauge should go to a 150 so you should be able to read the same pressure with both gauges hooked to the same port.

Now with readings like your describing, if something were wrong with the ac system, it would have to be a clogged expansion valve ( or possibly a restricted drier ). What could be happening is the low(suction) side is being drawn down by the suction side of the compressor. With a restricted expansion valve, the refrigerant exiting the hi side of the compressor doesn't return through the system fast enough as it's trying to pass through a restriction and is "backing up", resulting in lower than normal low side pressure and higher than normal high side pressure.

 

[jreask]

Thanks for that. I will do some checking on the gauges and switch hoses and report back in the next couple of days. Thanks for your help.

JR

 

[Drcoffee]

I would purge the system, vacuum it down and recharge it with the correct amount of refrigerant. A little too low or a little too much and the ac wont run right.