Hello everyone! I recently purchased a 2003 E450 Transit Bus Conversion. (National Conversion type) it has the 7.3L diesel in it. When I purchased it, the last owner told me the AC needed recharged. I hooked up a set of manifold gauges and static pressures are approx. 70psi(60 degree ambient temp). My compressor will not engage unless I jump it from the battery. I began to add some R-134 to the low side it will not let it charge. Even when I jump the compressor, the pressures never change and it still will not accept a charge attempt. I have tested voltage at the low pressure switch (14volts). Any ideas to why the system will not take a charge even when compressor is manually engaged?

Thanks and looking forward to your replies!

 

If the compressor has took a dump it will not build pressure

Have you checked the high side to see if pressure is building?

 

Hey Rikster-7700! Thanks for your reply!

I can get the compressor clutch to engage when I jump it straight from the battery. My high side is reading the same as my low side. Now it is approx. 80psi on both the low and high side measured with a good set of manifold gauges. I believe my original post said 70psi on the system but now it is getting towards afternoon and the ambient temperature is rising and so therefore my pressures are increasing in reflection of that. I do not have any service manuals to tell me what exact pressure the cycle switch needs to close to send power to the compressor clutch but I would think 80psi would be plenty. I also cannot find any relay for the compressor clutch and the little information I have found online states that there is not a compressor clutch relay, that the cycle switch basically acts as the relay when it closes. So I am thinking I could potentially be facing a separate issue as to why my compressor clutch is not engaging on its own.

 

80 psi is more than enough to close the low side switch. The power to the compressor comes from the in-cab control, goes through the low side switch, then the high side switch, then to the compressor. If you have power at the high side switch, the low side switch is fine. If you have power at the high side switch but not at the compressor, either the high side switch is bad, or there's a wiring problem.

 

Thanks for the info Pikachu. I will go test power if I can find the HP switch. With this vehcicle being the Econoline front end, it is seemingly impossible to trace ac lines or see the back of the compressor to locate the HP switch to test for power. I know my compressor clutch has power to it because I was able to splice into the power wire approx a foot back from the connector and attach my split to the constant power(my battery) in order to bypass the system to see if the clutch would engage and it would engage just fine. Is there a different place that I should test that comes from the HP switch? The other thing that has me scratching my head is that even if I do have an issue with either HP or LP switch or wiring being the cause of my clutch not engaging, why wouldn't my pressures build with 80psi in the system and manually jumping the clutch off the battery?

 

I wish I could tell you where the high side switch is on a van, but I've never had to do any A/C work on on E-Series. With the compressor running, you should at least see a pressure drop on the low side.

 

I am going to address the last first. **Please be careful! **


The High Side Pressure Switch is in the back close to the firewall


The Low Pressure and Compressor Cycling Switch are side by side on the Low Pressure Return Circuit.



How did he know? There must be a leak (or perceived leak) by him.


Did he indicate he had it looked at by a Trained Professional?



Static pressure really means nothing other than you do have pressure above 14.7 aP. This is a reasonable reading (you didn't state the humidity).


When running you should have seen: 25 - 35 PSIG Low Side / 135-155 PSIG High-Side is for 60*F 30% Humidity for 134a



Check the Plug at the High Pressure Switch. Notorious for failed connectors. You really have to look closely and test as the pins become loose and the spades become widened.



1. It could already be charged and its not allowing the system any more.


2. The Orifice Tube, Condenser, Dryer, or Evaporator could be clogged.

4. You could have a defective Low-Pressure Switch.


3 You should evacuate the system and inspected for "Black Death" (Orifice Tube Blocking). That will pretty much provide a inside view of the system and the compressor.


Again, these connector and pins are very finicky.




On the positive side the parts for our systems are relatively inexpensive. Like you can get a complete system (Quality) for $500.00

 

***Update***

I went out and jumped the low pressure sensor connector and I heard a noise that sounded like an ac clutch engaging. The only issue is that the clutch on the compressor was not engaging, or so I thought. Upon closer examination, the vehicle has 2 compressors. The clutch that was engaging was hidden at the top but under the air intake so I did not see it until I heard the sound of a clutch engaging. So that brought me to scratching my head. If this vehicle has 2 compressors, it must have 2 separate sytems. 2 high/low lines, accumulators, ports, ect ect. So I crawled under the vehicle and towards the back of the bus I found 2 AC ports. I hooked up my manifold gauges and low/high was 10psi. I added Freon and the ac clutch that I had been previously jumping and wondering why my pressures weren't changing, engaged. So everything started making sense. The one system had a bad pressure switch and the 2nd system was out of Freon. By not knowing there was two separate systems(I just bought this last week), I was jumping the clutch of the rear system and my gauges were hooked up to the front ac system and I was wondering how in the world I was manually operating the clutch and my pressures weren't changing. I ordered a new LP switch and I will install it and update everyone but it seems as if everything will be fine. I am getting engagement from both systems and pressures are looking good!

 

Well that explains it, lol.

 

The one problem you will eventually have to face is finding the leak in the rear system. Compressor shaft seals start to fail when the bearing or clutch start going south (if the clutch overheats, goodby seal). Another leak possibility is the charging port or the high pressure relief valve.

 

Or the condenser, or the evap coil, or the lines, or . . .

It's worth it to invest in a refrigerant sniffer.

 

Here's another update*****

After charging up the system, the front AC starting blowing hot again. I found that in a rubber AC line on the low pressure side had rubbed up against a pulley bracket and rubbed a hole in the line. I was able to replace the rubber line. Ever since, I can't can't get my compressor to engage again. I don't have any spec sheets on this since I just bought it but it does say on a sticker on top of the grill that the front AC should have 40psi. I have added freon via a cheap low side add device and I have a nice set of manifold guages. The ambient temp outside is approx 95 degrees and my manifold guages are reading a static of 100 but my compressor will not engage. I have power at my low side switch and high side switch but no power at my compressor clutch. I tried to jump the clutch running a wire straight to the clutch from the battery with no luck. I would say my clutch is locked up but I can turn it by hand and I do not have power at my connector. Any ideas? Thanks guys!

 

Since you applied power to the clutch and it did not pull in, the clutch is bad. Power directly from the battery bypasses the low and high pressure cutout safeties.

You likely have other problems, perhaps the clutch relay is also bad. When the clutch coil fails, the overcorrect can take out the relay or the fuse-I assume you checked the AC fuse.

This may not apply to your situation, but after fixing the leak, did you evacuate the system with a vacuum pump? Air + moisture does not make a happy AC system.