Drew9464

Im a new member and longtime lurker to this site. I need some advice.

My 2006 CRV AC took to a fatal compressor failure and I've just completed the replacement of the compressor (new Keihin), evaporator, expansion valve, condensor and low and high pressure lines. I performed servicing on the system and I have a question on my pressure readings. I've looked through numerous threads and found sage information, but I'm having a little trouble interpreting my numbers.

I vacuumed the system and left in place for hours in 100+ temps this past weekend. System hold tight. I serviced with R134A from a 30lb can until I was able to lower my duct temp to 50*. I let that stabilize and at 1800 rpm I added slowly until my center duct temp dropped to about 40*. Once I reached that point, I reduced my rpm to idle and my gages read as follows. Outside temp was 92* at night.





2006 CRV idle ac pressures

After I ran this on the interstate for 15 minutes I came back and read these numbers at 1800 rpm.




1800 rpm

I noticed that the compressor would shutoff once the duct temp approached 40* and would cutback on after the temp rose 2-4* to approx.44*. If I left the blower fan at max and not on recirculate, the compressor seemed to run continuiously and duct temp stayed between 46-50*. I realize that as a drive, the condensor would probably drop the high pressure somewhat because of the cooling effect.

My concern is are these numbers too low and high (spread) that I should worry about? Is my compressor cutting back because of low evaporator temps, or low pressures on the suction line? If its the low evaporator temp, is this normal operation and no concern?

This is my first efforts with ac work, but I'm a 40+ year aircraft mechanic that has potential... I hope.

Thanks for any advice.............

stangrcr1

It is cutting out on low pressure. Pressures look normal. Nothing to worry about unless there is a leak. It is working well. I might consider a couple more ounces of refrigerant if you want it really cold.

Are you trying to make the CRV a refrigerator?

Drew9464

If I add additional freon, my center duct temp starts to comes up. How high should I allow my stabilized center duct temp to go? Did I err in adding the freon just to the point of achieving my lowest duct temp? Does this model use a temp sensor circuit to help regulate the cabin temp or is it only a mix valve on the heater core with the compressor running all the time?

slowcivic2k

You should only charge by weight. Honda has no specific superheat specification to charge based on pressures, so you cannot introduce refrigerant into the system like this accurately.

Looking at your first picture:

The low side pressure is quite low, as is the high side for that temperature. Here is something you will need to consider. When the vehicle interior is cold already, the low side pressure will drop in an attempt to absorb heat. If it cannot, the pressure will continue to drop until it can. You will notice the high side pressure will also fall as well, because no heat is being added to the refrigerant. In short, the system in that state has cooled the car as much as it can without the low side pressure dropping lower and freezing up the evaporator.

The second pic:

The low side is definitely freezing up, but the pressure needs to be that low to still transfer heat, as evidenced by the slightly higher high side pressure. If you use fresh air after this test, the low side should come up, and the high side might fall a slight amount if any. Running the system like this will damage the compressor over time, you must feed it fresh air to give it some actual work to do.

Based on the readings, the level of refrigerant is correct. If it were too low, you'd have a higher low side pressure, and a lower high side as well. Too much refrigerant normally manifests as excessive high side pressure. The expansion valve in this case will only let so much refrigerant in, the rest builds up on the high side waiting to pass through.

If you continue to blow warm air from the outside, the low side pressure will increase, as will the high side. You should leave the recirculation off while driving to prevent the clutch from cycling off and on due to freezing (30psi is enough to freeze). At highway speeds with recirculation no the low side can get very very low when the car is already cold.

At first startup on most Honda's I service will have around 45-55psi initially, and this value will fall as the vehicle cools off. After this point a 25-40psi low side is normal. The high side will act the same way: It will stay high as long as heat is being transferred. Once the vehicle cools off, the high side pressure will drop because there is no more heat to transfer.

A 40 degree drop in that type of heat without the sun is excellent. When the replaced the evaporator there will be a small thermistor that clips to the evaporator. It is VERY IMPORTANT that this be attached in the right location. If you have an amblient air temp sensor is will be located near your right knee area. It will look like a small vent.