AC Diagnostic Help Needed

[michael0584]

The AC on my wife's 2011 Toyota Sienna is not blowing cold. It has had intermittent issues like this in the past and was low on freon. I've had to add freon twice in about 1.5yrs. I added a can about 2 weeks ago and low pressure side was 45 after the can. I didn't check high side. It was about 95 outside. About a week ago we were in traffic and it was not cooling. It finally started to cool down. Today it stopped cooling again. It was 108 outside and low side pressure was about 50 and high side was 160. Compressor running but blowing hot air and lines not condensating. Anyone know what would cause the low side pressure to be normal and high side to be low. Bad compressor? Thanks

 

[michael0584]

Oh forgot to mention this system has an expansion valve not a orafice tube and front and rear air both blow hot.

 

[6872xtc]

I don't have much experience, but I would start to think that possibly the compressor shaft seal may be worn and letting freon leak out and that you may also be experiencing a worn compressor itself.

 

[waybad1]

I always start with an evac and recharge first. I want to know exactly how much freon is in the system. I had to let freon out of one the other day that
the lady said had never been serviced.

 

[brans87]

Check ac relay. Toyota is known for problems with there ac relay just like Honda is also.

Wife's crv she had before got totaled ac work night before next day nothing. I pulled relay and swapped with another since was Sunday and at Home Depot. Instant ac again!

 

[Firdaddy]

You said it stopped working in traffic? You might check to see if the fans are working when the ac is on.

 

[michael0584]

Both fans are running and compressor is on. I would assume if compressor is running than relay should be fine? Or what else would relay control?

 

[Blue85]

If the lines to the evap are cold, the system is working. There could be a problem with blend door actuators that don't let you get cold air. If the compressor is running and the low side lines aren't cold, something is hokey with the charge. If refrigerant is low, the compressor will cycle in short bursts.

 

[michael0584]

Evap lines are not cold and the compressor is running constantly and not cycling. If I disconnect the pressure switch the compressor turns off and pressure starts the equalize. (Well low pressure goes up to about 110 but high pressure doesn't really move) plug switch back in and compressor cuts back on and brings low pressure down to 50. No change in high pressure.

 

[6872xtc]

I just think that the low side number should be lower for what the high side is reading.

 

[Chevy305]

Interesting problem. I'd agree with the others that the compressor and or the expansion valve could be the culprit, but I'd look at the condition of the evaporator too. Any dirt, bugs, leaves, etc blocking it?

Do you have an infrared temp gun? Shoot the lines on the high and low side, in and out of the evap, in and out of the condenser and see if the temperature corresponds correctly with the pressure.
Also while just sitting and reving the engine on a hot day while testing the A/C, it helps A LOT to set up a garden hose gently spraying into the grill to wet the condenser as the cool water will remove a lot more heat out of the charge than just the fans.

 

[Blue85]

2 things come to mind.

1) you don't have nearly enough pressure difference between high and low side. Over 100 degrees out, that high side should be over 250psi. The compressor keeps running because the low side never gets low enough for it to shut off.

2) the temps have to match the pressure or the charge isn't all R134. If the low side is about 50psi, it's about 52 degrees. That should be noticeably cooler than ambient. 160 psi may just feel like other under-hood temps.

If you were under-charged, the low side pressure would drop quickly once the compressor kicks on. If you were over-charged, the high side pressure would be too high. If you didn't have enough airflow, both pressures would be high. If there was a blockage in the system you would have very large pressure differences.

The lack of pressure difference means either the TXV or compressor is bad. If the TXV was blocked, you should see large pressure changes and quite quickly. If it was stuck open, the lack of pressure difference would be explained, but the evap should be frosty. So maybe the rings on the compressor are going.

 

[michael0584]

2 things come to mind.

1) you don't have nearly enough pressure difference between high and low side. Over 100 degrees out, that high side should be over 250psi. The compressor keeps running because the low side never gets low enough for it to shut off.

2) the temps have to match the pressure or the charge isn't all R134. If the low side is about 50psi, it's about 52 degrees. That should be noticeably cooler than ambient. 160 psi may just feel like other under-hood temps.

If you were under-charged, the low side pressure would drop quickly once the compressor kicks on. If you were over-charged, the high side pressure would be too high. If you didn't have enough airflow, both pressures would be high. If there was a blockage in the system you would have very large pressure differences.

The lack of pressure difference means either the TXV or compressor is bad. If the TXV was blocked, you should see large pressure changes and quite quickly. If it was stuck open, the lack of pressure difference would be explained, but the evap should be frosty. So maybe the rings on the compressor are going.

I'm think it's the compressor as well.

 

[blazer74]

Low high side with normal to high low side at that temp is poor compressor output.


Could be a blockage at compressor inlet. Sometimes ther is a screen there.

Gage's should equalize with the system off shows either a gage problem or a restriction. If they eventually equalize, think would be a restriction or blockage .

Too much oil if you added can cause an oil slug causing issues.

Inlet and outlet of evap should be about the same temp with a normal system.

Any cold isolated spots other than. The exp valve or orifice is a restriction.

Look for oil staining somewhere for a leak.

Just replaced a compressor for leaking at the front seal, didn't catch it the first time, pressures were normal tho.

 

[blazer74]

 

[michael0584]

replaced the compressor with a new Denso, Charged system with about 29oz freon (specs say 25-30oz). Low side pressure was 30, high side 85. system was barely cooling and if i recall high side line was sweating. Went back to verify this morning and not cooling at all this morning but compressor is running, lines not sweating. Checked all under the hood for leaks with my leak detector. No signs of leaks, but have not checked lines for rear air. I need to go out and verify pressure today but i bet its the same. It seems to cool and not cool when it wants to but when it does cool it's not very good. Leaning towards expansion valve but think there may be 2 in the system (front and rear air). So not sure which could be sticking (neither is cooling). Lines looked all clean inside, oil looked clean in old compressor and screen in compressor was perfectly clean.

 

[frankin5]

with the motor off, does the pressure equal out.

 

[Blue85]

high side line was sweating.

What the heck?

Did you flush the system while it was open? Just wondering if something is jammed in a line somewhere. Sweating only comes from cooling and cooling only comes from pressure + a restriction. If the old compressor blew chunks, that would explain the crappy pressures you had before and also why it's like a twilight zone A/C now. You always flush the evap, condensor and lines after a compressor pukes.

 

[blazer74]

85 high side?
My first thought sweating on the high side also?
Looks like 26.5 oz for 2011 so your close.

 

[udy2554]

Evacuate and get system under vacuum! If system doesn't hold vacuum (indefinitely), there is a leak or non-condensibles in system! Any moisture or non-condensible can cause a blockage! Get the system clean and leak-free, THEN charge to specs!