Windstar A/C question

Howdy from Hot Texas. Texican Tom here. I have question on my windstars a/c. What should the low side pressure read with the clutch running and what should the max pressure be on the low side with the compressor off. My compressor is cycling. On runs for about 10 seconds and stays off for 20 to 25 seconds. Any one out there that can help a recent lay offee?

Howdy Pard -

I recently had the same situation with a short cycle clutch engagement.

I added two cans (24oz) R134 and problem solved. With the clutch engaged it runs about 55psi and with the clutch off it's about 25-30psi. The A/C works great - and cycles as it should.

Also - once you add the R134 - make sure your low speed cooling fans come on with the A/C running. In your climate making sure those fans are operational is critical. Without those fans running the A/C won't function properly (increased heat = increased pressure in the A/C system) and you run the additional risk of overheating the engine and tranny.

Good Luck-
Glenn

With the system "off" (the clutch not engaged), it can be hard to predict what the pressure might be. If left "off" long enough the entire loop would come to the same pressure ... and that would be totally dependent on the temperature underhood ... 100 psi or more.

As the clutch engages, the pressure is pulled lower and lower ... but if it ever reaches as low as 25 psi, the low pressure cut-out will disengage the clutch again. As the poster above says, this usually indicates too little refrigerant. On a "good" system, with all the doors open and the cabin fan on "high", the pressure should get down to around 30 psi ... and the clutch should stay engaged, never cycling.

I'll add my confirmation to the above posts. The Ford A/C system regulates by cycling the compressor clutch, which is tied to the low side pressure. When the clutch initially engages the low side pressure will fall. When it falls below a low threshold (something like 20 psi) the clutch opens allowing the pressure to increase. When it exceeds the high threshold (~ 40psi) it re-engages the clutch. This cycle continue throughout operation of the A/C. It allows the A/C system to provide the amount of cooling needed for the ambient and cabin conditions, fan settings, vehicle speed without freezing the coils, and helps to prevent damage to the compressor. The Ford Service Manual gives the cycling periods for troubleshooting purposes, which vary according to the ambient air conditions.

As mentioned, it is critical that the fans engage when the A/C is turned on. The fans should remain on whenever the vehicle is not moving as long as the A/C is enabled. (regardless of the status of the compressor clutch) The only condition where the fans are turned of is when the speed exceeds ~50 mph. I recently had a problem where my A/C system was not working due to failure of the low speed dropping resistor. The fans worked normally when the engine temperature was high, but not for the A/C.

The science geek in me likes to chart out the pressures and temperatures of a system on the R-134A P-E curve (for example, like this: http://www.achrnews.com/NEWS/2004/40/Files/Images/113484.jpg)
However, you should be able to tell if the system is charged enough by feeling the two pipes carrying refrigerent through the firewall. One of them has the expansion orphice and should be very cold (i.e. just above freezing) while the other one will be cold, but not quite as cold as the first. The both should be cold enough for dew to form. If the first one is cold, but the second one is not, then you probably need more charge. If the first one is frosted, you could have water vapor in your system (which requires an evacuation and possibly a new accumulator).