1994 4.0 HVAC problems

I am in full springtime and the heater & AC are not working.

  1. With the key in the ACC accessory position and the fan set to the off position there is a constant rhythmic blowing every few seconds. This happens regardless of the position of the temp selector switch.
  2. This constant rhythmic blowing only occurs if the Fan Selector Switch is set to the off position.
  3. Unless the car is turned on and and at a sufficient operating temperature the Temperature Selector Knob is kind of irrelevant.
  4. With the car warmed and temp selector set to 85 calling for high heat the system is only producing uke warm air.
  5. With the car warmed and temp selector set to 65 calling for AC, at best the system is producing ambient temperature air.
  6. With the car turned on the voltage gauge shows a spike in voltage draw at every blowing interval with the fan selector set to the off position. If the lights are turned on they too will dim at every current draw interval

I don’t know where to start

it sounds like your blower control has failed which is part of the blower on xjs’s.


Thanks for the starting point. I’ll report back after I dig into it.

I tried to post a video of the problem but there doesn’t seem to be any provision for doing so.

After checking that all of fuses associated with the AC system were operable I switched out the relay on the fender wall. Removing the relay stopped the clicking that was trying to get the compressor to engage but satanic breathing that occurs every 5-10 inside the cabin never went away.

I pulled the climate control module from under the dash on the right side of the tunnel DAC10838 and swapped it for another CCM that I got from my 94 XJ40 parts car and the compressor stopped clicking and demon inside the cabin was exorcised.

The new symptoms from swapping out the CCM are the right side passenger face blower all but non existent and the system is producing hot air in regardless of temp setting.

This is the CCM that I pulled out of the car

This is the CCM that I swapped into the car from the XJ40

I don’t know how to test any of these CCM’s but it does seem as though there is a problem with the (AFAIK) original.

Where can I go to have it repaired?

It seems the XJ40 CCM didn’t show up for some reason

First report I can recall of an issue with that CCM. I hope someone here can offer some help getting it fixed. Please keep us informed.

After long and hard searching I finally found a used replacement CCM unit that seems to have brought the hvac system around to performing normally. I also someone to repair the old unit. Once it’s returned I’ll report back on the results.

I also found the heater control valve to be defective so that was changed as well.

The next problem is the I’m still getting hot air from the ac unit so I’m in the process of pulling the radiator to clean all the crud out of the fins of both the radiator and the condenser.

I want to evacuate and recharge the system but I’m confused as to weather or not the ac system was converted to 134a or not.

The sticker under the hood looks like this:

The low side and high side connections seems to look like 134a:

If the car originally was fitted with R12 I would rather return to that setup if I can. How can I verify what’s what?

Sticker says it was R12 originally. If it was swapped to R134, a shop would normally put a sticker saying so. But. If the PO did it he may very well have not.

R12 has come down considerably in price as there are fewer systems that use it any more. But it is only available to those with the proper EPA certificate. You’d have to go to a shop to get it installed. Use by an unlicensed person can result in hefty fines if the feds ever found out blah blah blah. Before going far you should pressure test the system with N2 and see if it will hold. If not then finding the leak(s) will be the first order of business. Then fixing, flushing, then addition of the proper compressor oil for which refrigerant you decide to use and then vacuum and install refrigerant.

If it currently has some charge but the suction side is warm it could be a bad valve in the compressor or a broken orifice tube or TXV ( thermostatic expansion valve). I can’t remember which of the two are used on the XK40.

Just saw the picture of the connections.Yes They are 134 connections. PO did the swap. so a little easier. See if there is any pressure. See if enough for the clutch to engage. If so check pressures and compare to what they should be. Around 40 45 psi low side. I forget the high side. Somebody can help here. If not then I’d start looking at the compressor valves or the orifice device

Well, I am the third owner and the car came from California so I’m surprised there isn’t any conversion sticker.

What is N2?

I can’t make heads or tails of the expansion valve. Does it look like a 13

Does the expansion valve look like 134a or R12?

Coulda been any of the POs that changed it. Whoever did didn’t put a sticker on it and of course the other(s) didn’t or even cross through with a marker. Not unusual

But the fittings are definitely R134.

N2 is nitrogen. It’s used instead of air when pressure testing. Air can react with old Freon and form acids. You will have to evacuate the system afterwards anyway but N2 is what is normally used

The 134 swap kits supplied back in the 90s never included the TXV, so it’s going to be for R12 unless professionally done and I think the sticker, or lack thereof noting the change says something there.

R134 in an R12 system was never really great. Between the TXV/oriface, evaporator and condenser mismatches, you get something that works but never as good as one designed for the correct refrigerant. I did the swap in my ‘91 with a product called Freez12. It was a mixture of 134a and at least one other component that was designed to come close to the adiabatic curves of R 12. It was ok,not great, and when you use a mixture generally you get changes in the mix when leaks occur. You have to evacuate it all and replace with new. You can’t top it off

Does the system have any charge at the moment?

I have don’t have a 134a manifold gauge set so I don’t if the system has anything in it yet. I do have a Robinair 134a refrigerant recovery-recycling-recharging machine, though. I’m waiting to get some new oil for the pump and a new filter for it before I hook it up, though. I also have R12 machine that needs oil and a filter as well. That’s why I have some interest in converting back to R12.

As far as I can tell the condenser looks to be original and not a parallel flow that’s compatible with R134a which is another reason for the concern of the expansion valve.

You think the expansion valve in the photo looks like it’s the one for R12?
If so, I’m thinking that if I can get the system flushed out, and maybe change the hoses I should be good to for a recharge?

Why on Earth would you want to do that?

Well, from the looks of things it seems like the R134a conversion was done by only changing the charge ports and the oil in the compressor. If that’s the case then changing the oil and removing the charge ports makes it easy.

What’s wrong with R12?

I assume, I don’t know, the TXV is for R12 since I’ve never known anyone back then to take the time to change them. Yes you could recharge with R12 AFTER you pressure test the system. You don’t want to fill it with refrigerant just to have it leak out. And you also need the correct oil if you are flushing it.

The issue with R12 is that it is still much more expensive than 134a although it has come down from the $800 a pound price it once was but it is also more difficult to come by. It sounds like you have some familiarity with HVAC systems if you have some of the equipment but you need to have a license to get the R12. You just can’t go into Walmart and by a can or two like you can with 134a

Yeah, because the expansion valve is kinda difficult to get to and the condenser isn’t a parallel flow I was going to let those two pieces be the determining factor as to which direction I was going to take in terms of refrigerant (path of least resistance). After checking my stash of refrigerant turns out my R12 tank is just about empty. That’s not necessarily game changer because there is plenty of R12 to be easily had from individual sellers and the 2.5 pounds that the system calls for is roughly $100.00.

As I put more thought into the matter there doesn’t seem to be a cheap way out. In order to prevent throwing good money after bad and end up with a trouble free system the expansion valve, hoses, condenser, and drier need to be changed. As far as I know custom barrier hoses along with a parallel flow condenser is mandatory with 134a and not to mention the increased performance that R12 derive from these pieces as well.

Correct me if I’m wrong but using N2 probably wouldn’t be necessary if all of the above components are changed. My thinking is I should be able to get away with a straight system flush prior to fitting the new components? After doing these things I imagine 134a could be more than acceptable. Besides, there is plenty of 134a in the stash.

So, at this point the real questions are as follows:

  1. Where can I get custom barrier hoses made
  2. Who makes a drop in parallel flow condenser for the XJS
  3. Is there a direct fit expansion valve replacement for 134a

When I converted mine, I was told I could just leave the R12 one there but the system would work better if I replaced it with an R-134a one. It was only a few bucks and the system would be needing evacuation and recharge anyway, so I did. After conversion, I’d get below 40 deg F at the vents within 30 seconds of startup. It’s incomprehensible to me that anyone would want to go to the effort to switch back. If you can’t hang meat in there, there’s something wrong, fix it.

Not the easiest job, no. I didn’t find it all that difficult, though, once I purchased this tool:

Used a crowfoot to hold the $%#%^ thing still while using this basin wrench attachment to loosen the B nut. Helps to remember these are O-ring joints, the tightness of the B nut is irrelevant to leakage, only need to be snugged enough to not rattle loose.

An issue, true enough, but I opted to address it by making very sure there was plenty of airflow by installing some serious electric fans.

Things went back and forth there. People who opted not to replace the hoses have reported no problem. The explanation is that the oil coats the inside of the hose and prevents the molecules of R-134a from penetrating. Moot here, though, because those hoses have been changed. The R-134a connections, without adapters, make that clear.

Jaguar, for the later XJ-S.

That was easy. These things are not unique to the XJ-S. Besides the fact you need one for R-134a and it needs to have both temp and pressure sensor connections, the only difference between model numbers seems to be the length of those temp and pressure tubes! It’s hard to find capillaries short enough for this application, but capillaries too long can simply be coiled up and fastened down so they don’t vibrate.

After sleeping on this expansion valve thing I searched online for the 95MY diagrams and it became clear as to what I was looking at in my own photos. I am now pretty confident that who ever converted the ac did indeed change the expansion valve to accommodate the R134a gas.

Thank you, thank you, thank you for clearing that up for me. I’ve never seen an ac conversion before and so, clearly I didn’t have a clue as to what the hell I was looking at. All along I was thinking that they just had to be adapters, silly me.

This newly realized info does put things in a different light, though. Instead of going crazy trying to dismantle the system and reinvent the wheel I’ll spend my time getting the recovery machine up and running and hook it up, pull a vacuum and find out if there are any leaks in the system.

After fixing the other associated issues I started the car and turned the ac on. Initially it blew cool air (not cold) for the first few minutes and from then on it blew hot up until the car was turned off some 5-10 minutes later.

This is Northern California car that was purchased by the second owner in 2001 for his wife where they lived in Sacramento. When I purchased the car in November 2018 it was said that for the most part it was fair weather occasional weekend car for his wife that guys wife was mainly driven with the top down. When I asked about the weirdness of the ac the response was that of bewilderment, and eventually it became clear that the ac system wasn’t on anyone’s radar screen, so it’s anyone’s guess as to how many years the hvac system hadn’t been functioning. All that to say that, over the course of a number of years I guess it’s reasonable to expect a fair amount of evaporation to the point of being empty, even.